Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Lightest Metal Leads to Big Change: Lithium‐Mediated Metal Oxides for Oxygen Evolution Reaction

Lightest Metal Leads to Big Change: Lithium‐Mediated Metal Oxides for Oxygen Evolution Reaction IntroductionThere is a global race to phase out the use of fossil fuels, with expectations of reducing emissions and the large amounts of environmentally polluting by‐products. Clean energy technologies, therefore, have received massive attention for the purpose of addressing global climate issues.[1] Owing to the abundance and carbon‐free nature of water sources, water electrolysis is becoming one of the most sustainable energy technologies.[2] On the one hand, water electrolysis is able to produce renewable hydrogen energy, which is promising to replace the conventional fossil fuels.[3] On the other hand, water splitting is usually based on the oxygen evolution reaction (OER), which synergistically limits the whole efficiency of water electrolysis due to its sluggish kinetics.[4] The multiple electron/proton exchange reactions of the OER have thus become a key challenge in water splitting. In order to improve the overall efficiency of water, many effective electrocatalysts have been investigated for improvement of the slow kinetics of the OER.To date, metal oxides (MOs) have shown outstanding electrocatalytic capability in water oxidation.[5] In particular, Ru/Ir‐based metal oxides have demonstrated a high catalytic activity and excellent durability of OER at an acidic proton exchange membrane (PEM) electrolyzer, but their high cost and resource scarcity requires developments of alternative catalysts with high cost‐effectiveness.[6] Therefore, a large number of studies have focused on layered hydroxides, chalcogenide oxides, spinel oxides, and amorphous Co‐based oxides.[7] Among these, bimetallic oxides (M1‐O‐M2) generally show higher electrical conductivity and catalytic activity than unmodified monometallic oxides.[8] These results indicate a close correlation between the electronic structure of the catalyst and the catalytic performance. Typically, M1‐O‐M2 type catalysts are originally prepared by occasional doping/substitution of exotic metals.[9] The exotic metals change the lattice parameters of the catalyst as well as the overlap between atomic orbitals.[10] 3d transition metals are by far the most widely used bimetallic oxides in OER processes. These metal ions typically have unsaturated coordination sites. These attractive structures have outstanding electron transfer rates and meanwhile, can serve as intermediate adsorption and activity centers for the OER.[11] Nikolov et al. have systematically investigated the M1‐O‐M2 effects. Through control of different elemental doping, the OER catalytic activities were tailored, resulting in a sequence of Co3O4 < NixCo3−xO4 < CuxCo3−xO4 < LixCo3−xO4.[12] In addition, structures with M1‐O‐M2 are likely to experience surface reconstruction due to the leaching effects, thereby generating dynamic remodeling to form the true active centers of the OER.[13] The introduction of M1 cations into M1‐O‐M2 oxides effectively changes the oxidation state of M2. For instance, some investigations have suggested that metal ions with high oxidation states usually indicate the presence of more active centers for the OER.[14] Moreover, by elaborate design of structure, the M1 cation can be removed during the activation of electrochemical process to re‐build a more dynamic surface toward the OER.[15] This irreversible reconstruction process was also believed to offer more benefits for the OER. These include effective changes in the local electronic structure, metal‐oxygen covalency, and hydrophilicity of the catalyst.[13b,16] In turn, these effects improve the adsorption and desorption capacity and the activation capacity of catalyst intermediates, which afterward determine their OER activity.[2b,13b,16]Lithium metal oxides (LMOs), well known as cathodes in lithium ion batteries, are now being extended to application as OER electrocatalysts due to their remarkable catalytic reactivity and following benefits: 1) compared to the previously reported OER catalysts, such as commercial IrO2[27] and RuO2.[17] transition metal alloy,[17,26] hydroxides[18,24] and phosphides,[19,25] LMOs show a highly concentrated high‐activity area with a low overpotential and a fast turn‐over efficiency (Figure 1a); 2) LMOs have been commercialized for many years due to the fast development of lithium ion batteries, thus LMOs are easy to scale up from either new production or recycled LMOs from battery wastes; and 3) LMOs catalysts are able to precisely quantify the chemical valence of transition metals through control the amount of lithium, thus tuning surface structures. Among the various M‐O‐M oxides, Li‐O‐M structures have shown unique chemical and physical features (Figure 1b). The insertion and extraction of lithium ions, synchronized with the valence changes of metals in LMOs, enable a novel controllable surface.[20] This structural reconstruction affects the local electronic structure and subsequently exposes the real active centers for the OER. This function finally tailors the molecular interactions involved in water oxidation.[21] In particular, the special layered structure of LMO can be exfoliated, forming single/few‐layer LMO. These properties intensively increase the number of active sites, resulting in an improved catalytic capability. In recent studies, more LMO electrocatalysts have been developed with different crystal structures (layered, spinel, etc.) formed by combining lithium with other noble or transition metals.[20,22] With deeper analysis and characterization, investigations on LMO have been quickly increasing to further improve the OER efficiency. This research includes dopant strategies, controlled removal of Li, and surface modifications.[20,23] This review summarizes recent advances in LMO materials for the OER. First, we briefly describe two different catalytic mechanisms for the OER (the adsorbate evolution mechanism [AEM] and the lattice oxygen mechanism [LOM]). We then outline the principles of bimetallic oxide modification in terms of electronic states, vacancies, bonding, lattice oxygen activation, surface reconstruction, and electrical conductivity. After that, we give a general overview of the historical development as well as the classification of LMOs, and describe specifically three methods of chemical modification of LMOs, focusing on dynamic surface reconstruction, the formation of lattice oxygen, and the valence evolution of active metal centers during the OER. Finally, we provide a perspective on the current challenges and future prospects of LMOs. We anticipate that this review will provide a comprehensive reference for the design of OER electrocatalysts and the development of polymetallic oxides.1Figurea) Catalytic activity comparison of typical OER catalysts and LMOs in aspects of overpotential and Tafel slope of transition metal LDHs,[24] transition metal phosphides,[19,25] transition metal alloys,[17,26] RuO2,[17] IrO2,[27] and lithium metal oxides at 10 mA cm−2. b) The overall clue of this review to understand LMO catalysts.General OER PathwaysThe OER typically involves four proton/electron coupling processes to produce molecular oxygen.[28] Under acidic conditions, two water molecules (H2O) are oxidized to produce four protons (H+) and one oxygen molecule (O2) (Equation (1)),[28b] while hydroxyl (OH−) groups act as oxygen sources in alkaline electrolytes (Equation (2)).[28a]In acidic solution, the total reaction formula for the OER is:12H2O=O2+4H++4e−\[\begin{array}{*{20}{c}}{2{{\rm{H}}_2}{\rm{O}} = {{\rm{O}}_2} + 4{{\rm{H}}^ + } + 4{{\rm{e}}^ - }}\end{array}\]In alkaline solution, the total reaction formula for the OER is:24OH−=O2+2H2O+4e−\[\begin{array}{*{20}{c}}{4{\rm{O}}{{\rm{H}}^ - } = {{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}} + 4{{\rm{e}}^ - }}\end{array}\]In this work, A bibliometric analysis[29] has been used to visually map the development of OER catalysts by selecting more than 5000 articles from the related topic area with titles, keywords, and abstracts in Web of Science (Figure 2a). The visualization mapping result indicates that various OER catalysts and different mechanisms have been proposed for the OER over the years, but it is generally accepted that there are two ways to understand the physicochemical processes of the OER: the AEM and the LOM (Figure 2b). It is worth noting that the lithium indicates a high occurrence in metal‐oxide‐based OER catalysts, suggesting its importance in the development of efficient water oxidation (Figure 2c). The AEM consists of four proton‐coupled electron transfer processes centered on metal ions, and oxygen is mainly derived from adsorbed water molecules.[30] With an AEM pathway, the reactant bodies, such as H2O and OH− groups, provide electrons and form an intermediate to release oxygen during the reaction. Specifically, water molecules pass through a single‐electron oxidation process and thus are adsorbed on the oxygen‐ligand metal (M) site of the electrocatalyst, forming an adsorbed *OH (step 1) (Figure 3a).[2b]2Figurea) Visualization map of OER catalyst network, b) keywords of different mechanisms, and c) the role of lithium in metal‐oxide‐based OER catalysts.3Figurea) Diagram of the AEM process. Reproduced with permission.[31] Copyright 2021, Royal Society of Chemistry. b) Reaction mechanism diagram of AEM and LOM on energy bands. Reproduced with permission.[32] Copyright 2020, Springer Nature. c–e) Schematic diagram of the LOM with three different mechanisms (oxygen vacancy site mechanism, single metal site mechanism, and dual metal site mechanism). Reproduced with permission.[31] Copyright 2021, Royal Society of Chemistry.The *OH is then oxidized to *O, followed by the formation of an *OOH intermediate through the adsorption of another water molecule (step 3). Finally, the *OOH adsorbed on the M site is oxidized, releasing oxygen, and the initially clean M site can be recovered (step 4). The stepwise process of the AEM presumably provides a way to distinguish the origins of the different catalyst activities. Typically, the ideal oxygen intermediate should be neither too strong nor too weak.[33] The catalyst surface in the conventional AEM mechanism is relatively stable, since only the metal center undergoes a valence change during the intermediate evolution of oxygen. For some catalysts, the AEM has been the commonly accepted mechanism and successfully helped to explain the OER pathway by illustrating the energy differences of intermediates. For some oxygen‐containing catalysts, more investigations have raised the question whether the lattice oxygen also participates in the reaction and forms O2. This mechanism, focusing on the different oxygen intermediate products, is called the LOM.[33a,34] It is notable that some oxygen‐containing catalysts can also work in the AEM process. For instance, when the energy position of the d‐band of the M in metal oxides is higher than the O p‐band, the metal sites mostly act as adsorption sites and active centers. This is because electrons from the p‐band are transferred to the d‐band. This change is able to produce ligand holes and thus facilitate the formation of oxygen‐containing species.[2b] In this way, the OER occurs on the surface of a metal site rather than on lattice oxygen, which fulfills the conditions for the AEM pathway. When a catalyst works in the opposite way, however, the OER follows the LOM mechanism (Figure 3b).[32] In the newly proposed LOM mechanism, the evolution of oxygen results in a change in its surface, where the OH−/H2O species will bind at the oxygen vacancies and be used as lattice oxygen for cycling.[31] Activation of the lattice oxygen is therefore a requirement for the successful triggering of the LOM pathway, which requires a catalyst host with LOM favorable structure. There are three main pathways for the LOM, depending on the different active centers of the catalyst.[15b,35] Activated lattice oxygen can act as a reaction center, which is referred to as the “oxygen vacancy mechanism”. Figure 3c depicts how OH− is adsorbed to form H2O directly. After the generation of O2, O vacancies are finally refilled by OH−. The cycling of this process continuously enables high efficiency in the OER. Alternatively, some catalysts allows direct coupling of *OO to lattice oxygen through surface deconstruction and subsequent deprotonation (Figure 3d).[35a,d] In addition to a single active center, some researchers have used a bimetallic site mechanism to explain the LOM.[35b] As shown in Figure 3e, coupling of adjacent active lattice oxygen can form M‐OO‐M, where the *OO* group that is formed usually acts as a peroxide.[15b]These conclusions mean that the OER pathway could be controllable through adjusting the electronic structures of catalysts. For example, the lattice oxygen is limited by the lower energy level of the oxygen p‐band center, or by the lower oxygen activity than the metal cation, so that the OER reaction is mainly by the AEM pathway.[32] In contrast, by escalating the central energy of oxygen close to the cationic d‐band of metals, the LOM may be triggered to free more lattice oxygen.Key Features of M1‐O‐M2 for OERSo far, MOs are one of the most effective kinds of OER catalysts because of their specific properties, which make them highly valuable for research on the electrolysis of water. The introduction of an extra metal has been reported as an effective strategy to bring about changes in the local electronic structure and thus enhance intrinsic properties by increasing electrical conductivity, creating vacancies, optimizing the morphology, and surface reconstruction.[10f,36] Interestingly, significant performance improvements have been further obtained by using bimetallic oxides (M1‐O‐M2) rather than monometallic catalysts. These improvements exist because the dopant effects of metals inevitably change the average or local lattice parameters, thus changing the overlap between atomic orbitals and leading to electron transfer.[10,37] For instance, the introduction of element A in AxByOz type catalysts could escalate the valence of the B metal to a high oxidation state, resulting in high TM‐O covalency, where TM stands for transition metal. This change thereby increases the rate of electron transfer.[14,38] Besides these considerations, ligand effects and strain effects of dual metal oxides have also been considered as reasons for the impact on their electrocatalytic activity toward the OER.[8,31] In this section, we systematically introduce representative key features of M1‐O‐M2 type catalysts. These features have been proved as important reasons that could directly affect the OER process. These key properties include electronic states, vacancies, bonds, lattice oxygen activation, surface reconstruction, and electrical conductivity.Electronic StateOrbital OccupancyIn general, the eg orbitals of transition metal ions in metal oxides are related to the σ‐bonding of anionic adsorbates.[39] The filling of eg orbitals can affect not only the binding of oxygen intermediates on the active metal sites, but also the local coordination geometry of the catalyst, which, in turn, can change the OER performance of the catalyst.[39b,40] The eg orbital filling of transition metal cations can usually change the OER performance, where the lower the filling rate of eg orbitals, the stronger the binding of intermediates to the oxide surface.[30c] In chalcogenide oxides, the rate determining step (RDS) is the process in which OOH adsorbates on the transition metal cation sites form OO bonds, and when the filling of eg orbitals approaches unity, the rate determining step (RDS) can be greatly promoted, resulting in the highest OER activity.[40b] In addition, in some spinel oxides, too little eg orbital electron filling (eg < 1) can limit the deprotonation step of M‐OOH−, but too much eg orbital electron filling (eg > 1) can limit the formation of OO bonds in M‐OOH−. The right balance between the rate‐limiting steps is obtained when the filling of eg orbitals is approximately equal to 1.[41] Usually, electron‐transfer initiated bond formation and dissociation in reactions, thus electron occupancy on the cracked orbitals, such as the t2g and eg orbital, is very important.[42] By adjusting the valence of transition metal oxides, the electron filling number on both eg and t2g orbitals can be changed. For example, the valence‐shift of Ni ions from +2 to +3 in spinel oxides NiCo2O4 can cause an electron loss eg orbital to create an electron vacancy (Figure 4a). As a result, the creation of vacant sites can optimize the adsorption energy barrier of intermediates, enhancing its OER performance.[43] Similarly, it has been reported that the orbital positions in LMOs can also be varied through the oxidation and reduction of transition metals (Figure 4b). For instance, the loss of electrons of the Ni, Co, and Mn ions in Li1.2Ni0.15Co0.1Mn0.55O2 reduce the electron occupancy in the eg orbital or in the t2g orbitals, producing not fully filled orbitals (Figure 4c).[44] The valence change of the typical bimetallic oxides mostly relies on the increase of voltage, which is difficult to precisely tune. Nevertheless, it is more controllable for LMOs to vary the chemical valence of the transition metal ions owing to the adjustable amount of lithium‐extractions.4Figurea) eg orbital occupancy of Ni in NiCo2O4. Reproduced with permission.[43] Copyright 2019, American Chemical Society; b,c) Redox couple evolution of Li1.2Ni0.15Co0.1Mn0.55O2 during cycling. Reproduced with permission.[44] Copyright 2018, Springer Nature.Spin StateIn general, increasing the spin state of transition metals can optimize the electronic configuration toward a better OER.[30c] Zeng et al. reported that the shift of Co3+ ions from the low spin state to the high spin state can increase the OER activity. This control is achieved by doping La atoms into cobalt oxides.[45] Interestingly, when the composition of LaCoO3 is further optimized to LaCo0.9Fe0.1O3 by introducing Fe (Figure 5a–c), the OER performance continues to improve through the enhancement of the CoO covalency.[46] Delithiation has also appeared as another strategy to change the spin status of transition metals.[47] For instance, delithiated Li1−xCoO2 promotes low spin Co3+ ions to Co4+ or medium spin Co3+ ions. This alteration can subsequently increase the OER performance. Also, Han et al. reported that the tips of LiCoO2 nanorods have higher OER activity, because the low‐spin Co3+ is mainly distributed on the sides, while the tips are mainly high‐ or medium‐spin Co3+.[48]5Figurea) Total density of states (TDOS) of Co ions in the low spin state in LaCoO3, and Co ions in the high spin state in LaCo0.9 Fe0.1O3. The insets represent the relationship between projected density of states (PDOS) and EF of LaCoO3 and LaCo0.9Fe0.1O3 from −1.5 to 1.5 V. b) Co d state and O p state PDOS in LaCoO3 and LaCo0.9Fe0.1O3, c) schematic diagram of Co 3d–O 2p overlap in LaCoO3 and LaCo0.9Fe0.1O3. Reproduced with permission.[46] Copyright 2017, American Chemical Society. d) Cyclic voltammograms of Co3O4, LT‐LiCoO2 and HT‐LiCoO2. e) Mechanism of OER on LT‐LiCoO2, and the qualitative one‐electron energy diagram of Li1−xCoO2. Reproduced with permission.[47] Copyright 2014, Macmillan Publishers Limited.Valence StateAccording to the principle of electroneutrality, interactions between elements can regulate the valence of transition metals. Transition metal oxides are usually active toward the OER because of their various oxidation states, their ability to adsorb intermediate products, and their easy participation in redox reactions.[30c] For example, the substitution of Ni on Co sites in spinel NixCo3−xO4 nanowires can increase the rate of electron exchange due to the higher oxidation status of the metals.[49] Some investigations have also suggested that tetravalent cations tend to be the active sites for the OER.[12,50] For instance, Na+ ion vacancies in this material resulted in more Co4+ centers in the CoO2 units of layered Na0.67CoO2 catalysts, which could shorten the OO length.[51] The short OO bonds facilitate the coupling between two adjacent metal‐oxygen O−O− interactions to form peroxide ions, without the need to generate oxygen by the conventional pathway (generation of OOH− species). During the OER process, the removal of Li will cause the change of the valence of transition metal ions (Figure 5d,e).[47] Lu et al. used electrochemical lithiation to tune the electronic structure of their catalyst by successively extracting lithium ions from LiCoO2 and converting the material to Li0.5CoO2 in organic electrolytes.[20] The presence of Co ions in the highly oxidized state increases its hydrophilicity toward oxygen species, resulting in easy binding to OH ions to form OOH, thus improving the OER performance. Zhu et al. prepared LiCo0.8Fe0.2O2 by using iron (Fe) doping.[52] The synergistic effect originating from the bimetallic structure raised the oxidation state of the cobalt.[52] In sum, a high oxidation state enables fewer electrons in the d‐orbitals, which directly determines the spin state and eg electron number.[53]VacanciesVacancies strongly affect the surface charge distribution of the catalysts.[35d,54] Attempts have been made to modify the structure of catalysts by introducing cationic vacancies.[55] For instance, Sn vacancies generated on SnCo0.9Fe0.1(OH)6 effectively increase the distribution of active sites and thus facilitate electron migration as well as the adsorption of reactants.[55a] SnCo0.9Fe0.1(OH)6 samples with Sn vacancies thus promote an increased OER performance over the initial sample. Strasser et al. prepared a unique porous NiIrO catalyst, where the leaching of nickel from NiIrO creates vacancies.[56] The presence of vacancies can shorten the IrO bonds and further enhance the catalyst performance. In addition, Qiao and co‐workers reported that the introduction of oxygen vacancies into CoO can effectively tune its electronic structure to enhance charge transfer and optimize the OER activity (Figure 6a,b).[57] As another example, researchers confirmed that the leaching out of Zn from ZnCo2O4 generates vacancies during the OER process, which activates the surface of the catalyst and increases the hydroxylation rate.[58] The OER performance of ZnCo2O4 was significantly higher than that of Co3O4. More results have indicated that ZnCo2O4 has more Co3+ than Co3O4 after the OER.[58] It has been confirmed that these Co3+ ions are the real active sites for the OER.[58] Vacancies in LMOs, including lithium and oxygen vacancy, also play an effective role in regulating electronic structures of the catalysts. For instance, lithium vacancies created in de‐lithiumed LiNiO2 lead to a larger charge deviation of the oxygen ligand and subsequently cause heterostructured interfaces of NiOOH species on the surface of LMOs. The reconstructed surface is able to stabilize the newly formed NiOO* intermediates, allowing an efficient and durable OER process (Figure 6c).[59] Layered LiCoO2 with abundant defects, including Co vacancies and oxygen vacancies, on the surface due to the exfoliation process. These generated defects usually enable more d‐band electron vacancies and enhance CoO covalency. The presence of Co vacancies can effectively improve the adsorption of intermediates, thus reducing the energy potential barrier for the rate‐determining step of OER.[60] By reducing the thickness, ultrathin LiCoO2 has an increased number of oxygen vacancies, which significantly enhances the OER kinetics due to the enriched d‐band holes. By introducing Li vacancies in LiNi0.5Co0.2Mn0.3O2, the transition metal ions can be oxidized to higher oxidation states, which significantly improves the oxidation performance.[61]6Figurea) Atomic configurations of O2 molecules. b) Estimated density of states on an original CoO surface and a CoO surface with O vacancies. Reproduced with permission.[57] Copyright 2016, Springer Nature. c) The schematic diagram of the evolution of LiNiO2. Reproduced with permission.[59a] Copyright 2020, Wiley‐VCH. d) Schematic illustration of the electrochemical tuning process of LiMPO4/rGO. Reproduced with permission.[62] Copyright 2015, Royal Society of Chemistry.BondsCovalent Metal‐Oxygen BondsIn general, the covalency of the metal‐oxygen bond is determined by the charge transfer energy (the energy difference between the unoccupied metal 3d center and the occupied O 2p center).[63] In metal oxides, the covalent mixing between the octahedrally coordinated metal cation and the oxygen anion can affect the exchange rate of neighboring ions.[30c] As discussed, M1‐O‐M2 structures lead to a redistribution of the electron density between the metal and the oxygen. Substitution with a metal that is more electronegative than the initial metal decreases the energy of the d‐band, leading to an enhancement of the M‐O covalency. Besides this, metal vacancies can also change the average (or local) chemical valence of the metal ions, which reduces the energy of the d‐band and enlarges the metal‐oxygen covalency. It has been recently reported that enhancing the CoO covalency by adding cationic vacancies can promote the OER activity of spinel oxides.[30c] Some researchers have shown that 10–30 at% Fe substitution can promote the covalency of CoO. In addition, the orbital hybridization and metal‐oxygen bond covalency of La (Mn, Fe, Co, Ni)O3 is related to the 3D electron distribution in the metal center.[64] In addition, it was observed from Y2−xSrxRu2O7 catalysts that the substitution of Sr2+ introduces vacancies into the lattice oxygen, which promotes RuO covalency and thus enhances the activity.[65] Electron energy band rearrangement can reduce the charge transfer energy and alter the interface charge‐transfer kinetics. Zheng et al. doped Mg into LiCoO2 materials to change the electronic structure of Co,[66] which synergistically enhanced the CoO covalency. Lithium mediated cobalt oxide (LiCoO2) can also promote CoO bonds to the fully covalent state,[20] thus reducing the energy gap between the metal 3d orbitals and the O 2p orbitals. This change promotes the OER activity. More lithiated materials, such as LiNi0.75Fe0.25PO4/rGO hybrid catalyst, where rGO is reduced graphene oxide, have also proved their enhanced OER performance (Figure 6d).[62] All these investigations are associated with a change in the transition metal valence and an increase in covalency between the metal and the oxygen.Distorted Lattice‐Oxygen NetworksDespite the oxygen vacancies, the de‐embedding of Li in layered LMOs materials triggers the lattice oxygen redox chemistry of OER.[14] The main reason is the oxygen network is severely distorted during de‐lithiation, forming peroxide‐like/superoxide species at the very end of the charge, eventually presenting short OO.[67] The short OO bonds facilitate the coupling between two adjacent metal‐oxygen OO interactions to form peroxide ions and enable a LOM pathway, instead of a conventional AEM pathway, which needs the generation of OOH* species.[51] The two metal sites on the bimetallic oxide undergo deprotonation, producing two oxygen species that combine to form an OO bond.[35b] In general, the lattice and electronic structure of materials can affect bonding, such as the bond length, bond angle and atomic distance. These features can affect the reaction path and the exchange of adjacent ions. In addition, exchange interactions between ions are influenced by wave function overlap. The longer the distance between protons (bond length), the less wave function overlap there is (Figure 7a).[51] The hole‐activated oxygen ligands can also become electrophilic, which will promote the formation of OO bonds and eventually enhance the OER activity of the catalyst.[59a] For instance, LiNiO2 generates Li1−xNiO2/g‐NiOOH during electrochemistry, with the formation of oxygen vacancies (Figure 7b). The oxygen vacancies can be filled by the massive migration of lattice oxygen. These active lattice oxygen can potentially trigger the generation of Ni4+, which can promote the deprotonation during OER,[68] leading to charge compensation effects by electron holes. These uncompensated electron holes on the oxygen atoms, thus, act as electrophilic centers to enhance the OER activity.[59a,14]7Figurea) The OO bonds shorter than 2.4 to 2.5 Å are highlighted with thick red lines. Reproduced with permission.[51] Copyright 2019, National Academy of Sciences. b) The OER process of LiNiO2. Reproduced with permission.[59a] Copyright 2020, Wiley‐VCH. c) Schematic of the electrochemical LMOs. Reproduced with permission.[69] Copyright 2014, Macmillan Publishers Limited. d) Schematic of Ru‐Co/LiCoO2. Reproduced with permission.[22b] Copyright 2022, Wiley‐VCH.Surface ReconstructionReconstruction usually refers to the surface changes of the electrocatalyst from its original morphology in terms of structure, components, and crystallinity during the actual reaction.[13b] Under strong oxidation conditions, most electrocatalysts undergo significant changes in their physicochemical properties (i.e., chemical composition and physical structure) of the surface during the OER.[2b,70] This change leads to a new surface reconfiguration. During the electrocatalyst reconstruction process, the change in components leads to the formation of new chemical bonds. These new chemical bonds finally alter the electronic features, as discussed above, leading to a strong improvement in the OER. Lithium ion de‐embedding during OER is a unique property of LMO materials. Usually, the lithium ion de‐embedding is accompanied by surface reconstruction during the charging process (Figure 7c). It is shown that both LT‐LiCoO2 and HT‐LiCoO2 undergo surface reconstruction in the first cycle of OER, producing Co3O4, which may be the active species for the reaction.[22a]Electrical ConductivityElectrical conductivity is an important indicator of catalyst efficiency. Excellent electrical conductivity requires an increase in the charge transfer rate and charge density, with electrons and holes determining whether there is good or bad conductivity. The rate of reaction in the OER and the electrical conductivity affect each other, and the rate of reaction can also affect the rate of charge transfer to the active sites on the catalyst surface. Many atoms in metal oxides exchange charge through orbital hybridization. M 3d and O 2p orbitals overlap with the strong electron part of the separated domain, which is commonly believed to result in high conductivity.[40a] Zhu et al. effectively enhanced the conductivity of LiCoO2 by introducing Fe. The coupling effect between iron and cobalt substantially increased its charge transfer rate.[52] In addition, the cationic coordination strategy allows us to control the local coordination and thus optimize the electronic structure of the catalyst. By doping Ru atoms in layered LiCoO2, there is a strong electronic coupling between the ruthenium and cobalt sites, which increase the electron conductivity of the catalyst (Figure 7d). The enhanced electron density can substantially optimize the binding energy and accelerate oxygen precipitation kinetics.[22b] In sum, the mobility of lithium works like “Dominoes”, leading to changes in various aspects, including electron re‐arrangements, oxygen activation, surface reconstruction and electronic conductivity. Understanding the structural uniqueness of LMOs rather than other metal oxides is very important to further optimize the OER performance of this class of catalysts (Figure 8).8FigureStructural features of LMOs and typical metal oxides.Emergence of Lithium Metal OxidesHistory of LMOAs discussed, M1‐O‐M2 type catalysts are a very important branch of the metal oxide family. The unique structural feasibility of M1‐O‐M2 structures as efficient OER catalysts has also been proved due to their optimized electronic structures. Li‐O‐M, as one of the M1‐O‐M2 oxides, has received massive attention due to its outstanding OER capability. As a typical cathode in lithium‐ion batteries, the electronic structure of LMO can be tuned by lithium intercalation and extraction, making it an intensively investigated OER catalyst (Figure 9).[71] In 2012, these researchers found that Li2Co2O4 consists of cubic Co4O4, while LiCoO2 consists of alternating layers of CoO and LiO octahedra.[72] In 2014, a de‐lithiated LiCoO2 (De‐LiCoO2) catalyst was first prepared through an electrochemical process to escalate the potential to a high level.[69] Compared with the original LiCoO2, De‐LiCoO2 has a lower overpotential and more significant catalytic properties. In addition, they introduced a variety of other transition metals into the pristine LiCoO2 and also obtained high OER catalytic activity. The unique electronic structure after delithiation is the key factor for the enhanced OER performance. In 2016, Gardner et al. found that partial delamination of unstable Li+ from layered LiCoO2 triggers surface reconstruction of LiCo2O4. Spinel and cubic lithium cobalt oxides retain the same cubic space group based on the [Co4O4]n+ cubic subunit, providing a lower Co4+ oxidation potential and lower cubic carbon pore mobility.[73] In contrast, the layered LiCoO2 has some problems with surface hole delocalization, which affects the synergistic facilitation of the electrons and holes in terms of entropy. Many previous studies have found that layered LiCoO2 is inert toward OER catalysis, and its catalytic activity is weaker than that of its spinel counterpart.[66,74] Lu et al., however, used electrochemical delithiation (De‐LCO) to enhance the active surface of layered LiCoO2 (LCO).[75] It was found that the more stable surfaces usually show little effect on their performance due to lithium content, while the more active surfaces are usually more dependent on lithium extraction. The extraction of lithium can increase the Co4+ sites and change the 2p state of active oxygen. Recently, Wang et al. adjusted the dynamic surface reorganization of layered LiCoO2 by precisely controlling the in situ catalyst leaching.[76] In the OER process, chlorine (Cl) dopant reduces the electrochemical potential of layered LiCoO2, thereby triggering in situ oxidation and delithiation of Co. In addition, the researchers successfully achieved the goal of preparing LMOs with high catalytic activity by controlling their morphology, doping, and electrochemical delithiation. These results indicate that LMOs have remarkable catalytic properties and are promising for applications in OER electrocatalysis.9FigureA timeline of major developments in lithium metal oxides. Reproduced with permission.[73] Copyright 2012, Wiley‐VCH; Reproduced with permission.[70] Copyright 2014, Macmillan Publishers Limited; Reproduced with permission.[62] Copyright 2015, Royal Society of Chemistry; Reproduced with permission.[52] Copyright 2015, Wiley‐VCH; Reproduced with permission.[80] Copyright 2017, American Chemical Society; Reproduced with permission.[76] Copyright 2017, American Chemical Society; Reproduced with permission.[66] Copyright 2019, Wiley‐VCH; Reproduced with permission.[79] Copyright 2020, Wiley‐VCH; Reproduced with permission.[78] Copyright 2020, Springer Nature; Reproduced with permission.[77] Copyright 2021, Springer Nature.LMO FamiliesA number of LMOs has been developed for use in high‐performance OER processes. Figure 10a summarizes all the elements that have been used for designing Li‐O‐M structures. Furthermore, LMO catalysts have also used as an efficient substrate to form LMO‐based composite or modified LMO (Figure 10b). These catalysts include: LMO with different phases, metal/non‐metal doped LMO, and LMO‐based heterostructures. The diversity of compositions and structures of LMOs provides design flexibility for the preparation of excellent OER catalysts.10Figurea) Elemental distribution of LMO families. b) Classification of LMO phases and composites, including: LMO,[23,61,72,77] metal/non‐metal doped LMO,[52,66,76] and LMO‐based heterostructure.[62,78] Reproduced with permission.[73] Copyright 2012, Wiley‐VCH; Reproduced with permission.[23] Copyright 2017, American Chemical Society; Reproduced with permission.[61] Copyright 2020, American Chemical Society; Reproduced with permission.[78] Copyright 2020, Springer Nature. Reproduced with permission.[52] Copyright 2015, Wiley‐VCH; Reproduced with permission.[66] Copyright 2019, Wiley‐VCH; Reproduced with permission.[77] Copyright 2021, Springer Nature. Reproduced with permission.[62] Copyright 2015, Royal Society of Chemistry; Reproduced with permission.[79] Copyright 2020, Wiley‐VCH.LMOLiCoO2 is the most classic LMO for the OER and is usually available in two different structures: layered LiCoO2 (HT‐LiCoO2) formed at high temperatures (800 °C) and spinel structured LiCoO2 (LT‐LiCoO2) formed at low temperatures (400 °C). Li+ occupies 16c octahedral sites of LT‐LiCoO2, and Co3+ occupies 16d octahedral sites of the spinel skeleton.[80] Studies have shown that LT‐LiCoO2 is composed of cubic Co4O4 units, while HT‐LiCoO2 consists of LiCo3O4 units.[47] The OER performance results indicate that the catalytic activity of layered HT‐LiCoO2 is not as good as that of LT‐LiCoO2, although they share the same OER mechanisms. The reason why LT‐LiCoO2 has better OER performance is because LT‐LiCoO2 offers easier surface reconstruction to form the real active centers.[22a] Similar to LiCoO2, LiNi0.5Co0.2Mn0.3O2 (NCM523) forms a spinel structure at low temperatures, which also shows promising OER activity.[81] In addition, it has been reported that the synergistic effects between Ni and Li can produce more defects on the surface, leading to a disordered but more active structure.[82] Huang et al. successfully synthesized three different structures of NCM523, named low‐temperature synthetic spinel NCM (LT‐NCM), high‐temperature synthetic lithium‐deficient disordered NCM (DO‐NCM) and high‐temperature layered hexagonal NCM (HT‐NCM) (Figure 11a).[62] DO‐NCM shows remarkable catalytic efficiency with a low onset potential of 1.48 V by shifting the valence of Ni2+ to Ni3+ through introducing lithium deficiency.11Figurea) Crystal structures of HT‐NCM, DO‐NCM, and LT‐NCM. Reproduced with permission.[61] Copyright 2020, American Chemical Society. b) Schematic diagram of LiCoO2‐NS, where NS stands for nanosheet. c) Atomic force microscope (AFM) image of LiCoO2‐NS. d) Electronic structure of LiCoO2‐NS. Reproduced with permission.[79] Copyright 2017, American Chemical Society.On decreasing the dimensions of LMO to ultra‐thin LMO nanosheets, oxygen vacancies and high‐spin Co4+ are generated, which can enhance oxygen adsorption (Figure 11b–d).[79] The overpotential of ultra‐thin LiCoO2 nanosheets is 0.41 V at 10 mA cm−2. Optimization of the morphologies of LMO can always trigger some interesting physical phenomena. For instance, researchers developed LiCoO2 nanorods to study the OER activity in alkaline solution.[48a] One of the interesting results that they found is that low‐index crystalline surfaces are formed in the sides while the tips mainly have surfaces with high‐index crystallinity. This phenomenon causes low‐spin Co3+ to be predominant on the lateral surface, while high‐spin or medium‐spin Co3+ forms at the tips.[48a–83] Investigations have shown that enhancement of TM‐O bond covalency can significantly improve the kinetics of the OER, but it is also accompanied by surface instability.[77,84] Yang et al. reported a solid electrocatalyst, α‐Li2IrO3, which reacts with water to form a birnessite phase during oxidation/delithiation (Figure 12a,b) and presents an overpotential of 290 mV at 10 mA cm−2.[77] Similarly, Gao et al. developed amorphous LiIrOx by doping lithium ions into iridium oxide,[85] which showed remarkable stability and activity toward the OER in acidic media (270 mV at 10 mA cm−2). The K ions in KOH solution are introduced into the catalyst structure during the electrolysis, in turn promoting the oxidation of water (Figure 12c). In addition to its remarkable stability, this solid electrocatalyst has indicated an effective strategy to improve OER catalytic activity. In this way, the conflict between the OER performance and stability of the catalyst is balanced.12Figurea) Structural model of Li1/3Ir2/3O2 layer. b) Schematic diagram of chemical oxidation of water by charge compensation. c) The connection between the battery system and the water system. Reproduced with permission.[77] Copyright 2020, Springer Nature. d) DFT optimized atomic structures of LiCoO1.8Cl0.2. e) Schematic diagram of the in situ surface reconstruction processes of LiCoO1.8Cl0.2. Reproduced with permission.[76] Copyright 2021, Springer Nature.Metal/Non‐Metal Doped LMODoping is another effective strategy to further improve the OER activity of LMO. The addition of other ions can tune the electronic structure of LMO, which impacts the binding energy of OER intermediates, the conductivity and the capability for electron‐transfer.[86] Doping with some nonmetallic ions has been reported as an effective strategy to improve the performance of the OER.[76] For instance, doping with Cl reduces the electrochemical potential of layered LiCoO2, thereby triggering in situ oxidation and delithiation of Co (Figure 12d,e).[76] This structure (LiCoO1.8Cl0.2) achieved an overpotential of 302 mV at a current density of 50 mA cm−2geo. In addition to anions, some metal cation doping can also effectively change the electronic structure of catalysts. Fe is often used as a dopant due to its abundant reserves and non‐polluting characteristics. For example, Fe doped LiCoO2 shows a unique synergistic coupling effect between Fe and Co,[53] resulting in an optimized electronic structure of Co with an increased rate of charge transfer. At the current density of 10 mA cm−2, the Fe‐doped LiCoO2 achieved an overpotential of 0.34 V with current density of 10 mA cm−2, showing better catalytic performance than a commercial IrO2 sample. In some reports. Al doped lithium nickel oxides were also fabricated, such as LiNi1−xAlxO2. This strategy is effective to suppress the mixing of Ni2+ in the Li+ layer but obtain a higher concentration of Ni3+. This has been considered as a key role to achieve excellent and stable OER activity.[87] Zheng et al. proposed a mechanical shear‐assisted exfoliation strategy to synthesize defect‐abundant atomic‐layered LiCoO2 (AD‐LCO).[60] Microscopic characterizations confirm the successfully fabricated defective LiCoO2 nanosheets (Figure 13a–d). Benefiting from the unique structural superiority, the obtained AD‐LCO exhibited superior OER activity and stability. In another work, combining doping engineering and shear‐force‐assisted exfoliation strategies, they developed a novel 2D Mg doped LiCoO2 (ELCMO) for oxygen electrocatalysis for the first time (Figure 13e).[66] Microscopic characterizations indicated the successful exfoliation of LiCoO2 from its bulk form to nanosheet morphology with a well‐maintained crystal structure. The synthesized ELCMO exhibited remarkable catalytic performance with an overpotential of only 329 mV at a current density of 10 mA cm−2 in 1 m KOH (Figure 13f). In this work, Mg dopant was believed to alter the electronic structure, which led to the enhanced Co 3d–O 2p covalency and hybridization (Figure 13g). Furthermore, the insertion and extraction of lithium ions from metal oxides is the other important feature that can improve the electronic structure and increase catalytic efficiency.[88]13FigureStructural and chemical characterizations of AD‐LCO. a) High‐resolution transmission electron microscope (HRTEM) image. b,c) High‐angle annular dark‐field‐scanning transmission electron microscope (HAADF‐STEM) images. d) Strain mapping of (c) Reproduced with permission.[60] Copyright 2022, Wiley‐VCH. Schematic illustration of the fabrication process for ELCMO. e) Illustration of fabrication process of ELCMO. f) LSV curves of ELCMO and reference samples. g) Qualitative one‐electron energy diagram. Reproduced with permission.[66] Copyright 2019, Wiley‐VCH.Similarly, the synergistic effects originating from extra Zn2+ dopant and Li+ in the spinel ZnCo2O4 resulted in charge deviation of the oxygen ligand and greater CoO covalency, owing to the charge compensation from transferring the oxygen charge to the octahedral Co center.[59b] Sun et al. reported another spinel Li0.5Zn0.5Fe0.125Co1.875O4, which showed excellent OER performance. This was achieved by promoting oxygen charge transfer to the active transition metal center through the co‐dopant method.[59b] In conclusion, the addition of Li ions and extra metal dopants can change the valence state of the original metal oxide or create vacancies, leading to stronger M‐O covalency.LMO‐Based HeterostructureHeterostructures, such as metal/metal (hydrogen) oxide systems, featuring strong electronic and geometric effects between metal and support, exhibit great advantages for enhancing catalytic activity and stability.[89] LMOs have also recently been deployed as a kind of versatile support to anchor metal species and tune the electronic structure. Zheng et al. successfully investigated a platinum (Pt)/LiCoO2 heterostructure consisting of homogeneous Pt nanoparticles confined by LiCoO2 nanosheets that was fabricated by a facile wet chemical strategy (Figure 14a).[78] Microscopic characterizations demonstrated that the Pt nanoparticles (NPs, ≈2.2 nm) were uniformly anchored on the LiCoO2 supports (Figure 14b–h). The obtained Pt/LiCoO2 heterostructures achieved an ultra‐low overpotential of 285 mV at a current density of 10 mA cm−2 (Figure 14i). The unique heterostructured Pt/LiCoO2 could act as an active‐center‐transferable electrocatalyst to accelerate both the hydrogen evolution reaction (HER) and the OER for hydrogen production (Figure 14j). In addition, the catalytic activity of the materials for the OER was significantly improved by Liu et al, through the continuous extraction of lithium ions from lithium transition metal phosphates.[62] In particular, Li(Ni, Fe)PO4 grown on rGO nanosheets exhibited remarkable activity and stability.14Figurea) Schematic diagram of the fabrication process for Pt/LiCoO2 heterostructures. b) SEM image of LiCoO2. c) Transmission electron microscope (TEM) image of exfoliated LiCoO2 nanosheets. d) TEM image of Pt/ Pt/LiCoO2. e) Selected area electron diffraction (SAED) pattern. f) Annular bright‐field (ABF)‐STEM and g) HAADF‐STEM image. h) Energy dispersive spectroscopy (EDS) elemental mapping of Co, O, and Pt. i) LSV curves of Pt/LiCoO2 samples and reference catalysts. j) Proposed catalytic mechanism for Pt/LiCoO2. Reproduced with permission.[78] Copyright 2020, Wiley‐VCH.Summary of OER Performance of LMOIn this section, we systematically compare the OER performance of typical metal oxides with M‐O,[90] M1‐O‐M2,[91] and Li‐O‐M structures.[13a,20,52,66,92] Figure 15a shows that dual metal oxides, including LMOs, can exhibit significantly improved performance compared to single metal oxides. Among them, the LMOs exhibit the lowest overpotential and Tafel slope, and the single metal oxides have high overpotential and a high Tafel slope. Synergistic effects between different metal sites can effectively overcome the kinetic deficiencies of the OER, such as modulating the electronic structure and increasing active centers.[93] As can be seen from the previous discussion, a significant proportion of research has been devoted to the doping of lithium ions into metal oxides to form bimetallic or polymetallic oxides. A long‐term durability of OER catalysts is another important features for proton exchange membrane (PEM) electrolyzer toward industrial applications.[6a] Catalysts, including LMOs, may undergo surface reconstruction during the OER process, which is effective in enhancing catalytic performance, but leads to catalyst instability. In addition, catalysts with more defects potentially have higher OER activity, but their stability is not fully satisfied. For these catalysts following the LOM pathway, it is more important to adjust the ligand structure to stabilize the lattice oxygen, and also to prepare more stable precursor supports to improve the durability. As shown in Figure 15b, chloride‐doped LiCoO1.8Cl indicates a highly stable OER performance over 500 h with a low potential at 1.5 V to achieve 10 mA cm−2. These results indicate the vital significance of LMO‐based OER catalysts in the future.[13a,20,23,47,52,61,62,66,75–77,85,87b,88,92,93b] Table 1 shows the OER performance of LMOs in recent years. Furthermore, Figure 15c,d ranks the overpotential and Tafel slope of various typical LMOs at 10 mA cm−2 current density.15Figurea) Overpotential and Tafel performance distributions of single metal oxides,[90] dual metal oxides,[91] and lithium metal oxides at 10 mA cm−2. b)  Stability of lithium metal oxides. c,d) Tafel slopes and overpotentials of lithium metal oxides at 10 mA cm−2.1TableSummary of OER performance of reported LMOsCatalystOverpotentialTafel slope [mV dec−1[ElectrolyteElectrodea)RefLiCo0.8Fe0.2O2340 mV (10 mA cm−2)500.1 m KOHGCE[52]LiCoO2430 mV (10 mA cm−2)830.1 m KOHGCE[52]LiNi0.8Al0.2O2340 mV (10 mA cm−2)440.1 m KOHGCE[87b]De‐LiCoO2380 mV(5 mA cm−2)500.1 m KOHCFP[20]De‐LiCo0.33Ni0.33Fe0.33O2300 mV(5 mA cm−2)350.1 m KOHCFP[20]De‐LiCo0.5Ni0.5O2370 mV(5 mA cm−2)420.1 m KOHCFP[20]De‐LiCo0.5Fe0.5O2340 mV(5 mA cm−2)400.1 m KOHCFP[20]LT‐LiCoO2520.1 m KOHGCE[47]LT‐Li0.5CoO2600.1 m KOHGCE[47]α‐Li2IrO3290 mV (10 mA cm−2)500.1 m KOHGCE[77]LiIrOx270 mV (10 mA cm−2)390.5 m H2SO4GCE[85]DO‐LiNi0.5Co0.2Mn0.3O2430 mV (10 mA cm−2)85.60.1 m KOHGCE[61]LT‐LiNi0.5Co0.2Mn0.3O2440 mV (1 mA cm−2)142.60.1 m KOHGCE[61]HT‐LiNi0.5Co0.2Mn0.3O2540 mV (1 mA cm−2)241.80.1 m KOHGCE[61]Exfoliated‐LiCo0.95Mg0.05O2329 mV (10 mA cm−2)33.81 m KOHGCE[66]LiCo0.95Mg0.05O263.71 m KOHGCE[66]Exfoliated‐LiCoO247.71 m KOHGCE[66]LiCoO2‐NS410 mV (10 mA cm−2)880.1 m KOHGCE[23]De‐LCO NPs390 mV (10 mA cm−2)570.1 m KOHCFP[75]30% Pt/LiCoO2285 mV (10 mA cm−2)46.81 m KOHGCE[92]LT‐LiCoO2430 mV (10 mA cm−2)481 m NaOHGCE[88]HT‐LiCoO2430 mV (10 mA cm−2)491 m NaOHGCE[88]LiCoO1.8Cl0.2270 mV (10 mA cm−2)55.41 m KOHGCE[13a]LiNi0.75Fe0.25PO4/rGO270 mV (10 mA cm−2)470.1 m KOHGCE[62]LiCo0.95Mg0.05O2329 mV (10 mA cm−2)1 m KOHGCE[66]1%La/LiCoO2330 mV (10 mA cm−2)1 m KOHGCE[94]a)GCE = glassy carbon electrode, CFP = carbon fiber papers.Chemistry behind LMO during the OERLMO‐based catalysts usually undergo chemical and structural evolution during the OER process, which is closely related to their activity and durability. Therefore, understanding the underlying surface chemistry is of critical significance to unravel the structure–performance relationships and establish a universal design strategy toward highly efficient electrocatalysts. In this section, we will unravel the surface chemistry of LMO during the OER from the aspects of lithium extraction, surface reconstruction, lattice oxygen activation, and oxidation state evolution (Figure 16).16FigureSchematic illustration of the chemistry behind changes to the LMO during the OER. Reproduced with permission.[66] Copyright 2019, Wiley‐VCH. Reproduced with permission.[61] Copyright 2020, American Chemical Society.Lithium Extraction and Surface ReconstructionSurface active sites determine the activity and selectivity of electrocatalyst–intermediate adsorption and stability. During the OER process, the electrocatalyst surface sites are completely dynamic in nature, which triggers reconstruction of the surface. Reconstruction connects the surface of the electrocatalyst with the real active sites involved in the OER process.[2b,70] The reconstruction process could trigger the evolution of the local electronic structure, coordination environment, M‐O covalency, and hydrophilicity of the catalyst.[13b,70b,95] Furthermore, the reconstruction process may change the surface of electrocatalyst reversibly or irreversibly, according to the structural characteristics of the electrocatalyst.[2b,96]For various metal oxides, the de‐embedding of lithium ions during the OER is a unique property of LMO materials. During the charging process, some of the lithium ions are extracted, and the negatively charged CoO generates stronger electrostatic repulsion, increasing the layer spacing. During the discharge process, lithium ions are intercalated and the lattice spacing is restored.[97] The stresses on the material can be quantitatively tuned by controlling the amount of de‐lithiation. Both compression and stretching can change the surface electronic structure, and thus the catalytic activity, by changing the distance between surface atoms.[97] Surface reconstruction accompanied by de‐lithiation can expose the true active center.[69] It was shown that both LT‐LiCoO2 and HT‐LiCoO2 undergo surface reformation in the first cycle of the OER, producing Co3O4, which may be the active species of the reaction.[22a] In addition, partial delamination of Li+ from layered LiCoO2 can complete the process of remodeling to cubic spinel LiCoO2.[73] Spinel‐type LiCo2O4 has a [Co4O4]n+ cubic subunit structure that provides a lower Co4+ oxidation potential. Many untreated LMOs do not have good performance, but cation or anion doping into LMOs can effectively change their electronic structure and trigger surface reconstruction, which, in turn, can enhance the OER performance of LMOs.[76,98] For example, doping with Cl− can reduce the potential for cobalt oxidation and lithium extraction.[76] The surface reconstruction of LiCoO2 without Cl− to spinel‐type Li1±xCo2O4 usually requires a higher electrochemical potential. In addition to this, the migration of Ir ions from the body to the surface in La2LiIrO6 catalyst leads to a drastic surface remodeling and the formation of IrO2 nanoparticles.[98]Activation of Lattice OxygenIt was found that the catalyst surface is no longer stable and changes dynamically with the OER process when following the LOM mechanism.[30c] The oxidation, exchange, and release of lattice oxygen ligands on the catalyst surface is critical to the OER performance.[98,99] The activation of lattice oxygen generally takes place at two adjacent metal sites, requiring the catalyst itself or the lattice oxygen itself to exhibit a unique electronic structure.[30c] Some LMO catalysts are able to allow direct coupling of *O intermediates and active lattice oxygen, and the newly formed *OO species become the O2 molecules produced in the subsequent OER cycle. In addition to this, the coupling of adjacent active lattice oxygen atoms can form M‐OO‐M, where *OO* molecules usually act as peroxides.[3c] The redox reactions of lattice oxygen can significantly enhance the OER activity, and some LMO catalysts can induce the activation of lattice oxygen by ligand cavities, and the electrophilic cavity‐active oxygen ligands can promote the formation of OO bonds.[98] For example, La2LiIrO6 undergoes dynamic reconstruction under oxidizing conditions, and the resulting electrostatic destabilization leads to a more significant effect on the O 2p band than the Ir 5d band, where surface oxygen ligand activation generates more ligand holes and iridium ion migration can activate lattice oxygen through ligand holes.[98] In addition, some researchers have found that lattice oxygen activation is more energetically favorable for high‐valence metal active sites by DFT calculations.[14] For example, LiNiO2 generates Li1−xNiO2/g‐NiOOH during the electrocatalytic process, and the high‐valence Ni ions in graphitic g‐NiOOH promote the formation of NiOO*. NiOOH completes deprotonation by forming ligand holes on the lattice oxygen to compensate the charge, which in turn promotes the OER activity.[59a]Change of Oxidation States in the MetalsAn increasing number of studies in the past have demonstrated that the oxidation state of the catalyst is related to the intrinsic activity of the OER.[14] Metal cations with higher oxidation states have higher metal‐oxygen covalency and thus lower charge transfer energy due to the contraction of the orbitals and shift of the valence band.[100] Among LMO catalysts, either the doping with other metal elements or the de‐embedding of lithium element is likely to regulate the oxidation state of the active metal cation. The higher the oxidation state of the cation, the easier it is to separate the electrons from the adsorbed oxygen ions.[101] The spinel‐structured LMOs have inherent mixed‐valence characteristics, with many gap sites favorable for cation migration.[102] Spinel‐type Li2Co2O4 will change from Co3+ to Co4+ oxidation state of the Co ions, with a change of voltage and the detachment of the Li ions during the OER process,[14] although the low spin state of Co ions and the edge‐sharing CoO network remain unchanged. Therefore, it can be inferred that the highly oxidized Co4+ site is the primary reason for the high catalytic activity of Li2Co2O4, rather than the Co3+ or oxygen vacancies.[14] In addition to lithium deoxidation, doping of LMOs can also effectively change their electronic structure.[87b] For example, doping Mg element into LiCoO2 can modulate the electronic structure of LiCoO2, where part of the Co3+ is oxidized to high‐valent Co4+, and also increases the CoO covalency. The OER performance of Mg‐doped LiCoO2 is significantly enhanced.[103] Al‐doped LiNiO2 transforms Ni3+/Ni2+ into Ni4+/Ni3+, and the Ni4+/Ni3+ octahedral sites in LiNi1−xAlxO2 are the real active centers of the OER, with the redox energy at the top of the O 2p band.[87b] In addition, some researchers found that the disordered structure of LiNi0.5Co0.2Mn0.3O2 has more significant OER properties than both its spinel counterpart and the layered LiNi0.5Co0.2Mn0.3O2. This is due to the presence of lithium vacancies in the disordered LiNi0.5Co0.2Mn0.3O2 crystal structure, which can change Ni ions from Ni2+ to Ni3+.[62]Conclusion and PerspectiveM‐O‐M type oxides typically exhibit significant catalytic properties compared to their unmodified counterparts, and the synergistic interaction between the metals will change the lattice parameters of the catalysts as well as the overlap between the atomic orbitals.[10] Notably, in a family of M‐O‐M oxides, lithium ions in LMOs can be inserted and extracted to produce irreversible changes in the catalyst surface, and the surface electronic structure will be significantly altered. In this paper, we review the recent research progress on LMO electrocatalysts. We not only outline the two OER mechanisms, AEM and LOM, but also summarize the modification principles of M‐O‐M type catalysts in terms of electronic states, vacancies, bonds, lattice oxygen activation, surface reconfiguration, and conductivity. In addition, we fully classify and summarize different types of LMOs and focus on their dynamic surface reconstruction, formation of lattice oxygen, and the valence evolution of active metal centers that LMOs undergo during the reaction process.Although extensive research progress has been made on various LMO catalysts used for the OER, most of the reported LMO catalysts have high overpotential, and their catalytic performance is still lower than the requirements of industrial applications. Although the activity of many reconstituted LMOs will increase, a decrease of stability may accompany this. In addition, the research and development of excellent electrocatalysts not only need flexible ideas and preparation methods, but also need advanced analysis technology. Therefore, in order to further improve the overall efficiency of the OER, we put forward two suggestions based on the existing problems:1)Designing new electrocatalysts. The reactions of many major metals lack the necessary combination of empty and full orbitals, so the catalytic OER is usually inert. Alkali and alkaline‐earth metals are traditionally used as thermal catalysts for organic reactions rather than as electrocatalysts. The active center of the catalysts is usually a 3d transition metal with variable valence, but doping with an alkali metal or alkaline earth metal can change the electronic structure of the electrocatalyst and increase the number of reaction sites, so that there is improvement of the slow dynamics of the OER.[51] The study of LMOs can effectively help us to understand the alkaline earth metal catalysts comprehensively and systematically, and provide a basis for a better understanding of their catalytic mechanism. Alkaline earth metals and alkali metals are candidates for highly active water electrolysis catalysts and the key to future research.2)Using in situ testing methods. OER is a complicated reacting system, which involves structural changes of catalysts, new phases formed on the interfaces, and absorbed small molecules. To gain a deep and empirical understanding of the OER chemistry, in situ techniques are urgently required (Figure 17). For example, LMOs undergo complex physicochemical changes during their electrochemical processes, and their true active centers are difficult to trace and identify. Thus, in situ X‐ray diffraction (XRD) and X‐ray absorption spectroscopy (XAS) testing techniques have been applied to the structural changes and oxidation of active sites of LMOs under OER conditions.[108] The oxidation of Ir to a higher oxidation state has been observed by in situ X‐ray absorption spectroscopy (XAS) in amorphous LiIrOx, but no such change was observed on IrO2.[108] Most of LMOs used for OER are composed of multiple metals. As the composition of catalysts becomes more complex, the difficulty is of defining the reaction paths. Therefore, in situ characterization techniques under OER conditions are necessary to monitor important intermediates, such as in situ Raman spectroscopy, ambient pressure X‐ray photoelectron spectroscopy (APXPS), and Mössbauer spectroscopy.[109] However, the currently existing in situ testing techniques have many limitations, and more characterization methods with high resolution are needed to monitor the dynamic structural evolution. Combining new in situ techniques with other characterizations can help researchers to understand more deeply with regard to the correlation between structure and activity of catalysts.17FigureSchematic illustration of in situ techniques, including: In situ Raman. Reproduced with permission.[101] Copyright 2017, American Chemical Society; In situ XAS. Reproduced with permission.[102] Copyright 2015, American Chemical Society; APXPS. Reproduced with permission.[103] Copyright 2015, American Chemical Society; and MÖssbauer spectroscopy. Reproduced with permission.[104] Copyright 2015, American Chemical Society.AcknowledgementsThis work is financially supported by the Beijing Municipal Natural Science Foundation (2212025). The authors thank Tania Silver for her critical reading and editing of this work.Open access publishing facilitated by University of Technology Sydney, as part of the Wiley ‐ University of Technology Sydney agreement via the Council of Australian University Librarians.Conflict of InterestThe authors declare no conflict of interest.a) M. Gong, H. Dai, Nano Res. 2015, 8, 23.b) S. Chu, Y. Cui, N. Liu, Nat. Mater. 2017, 16, 16;c) M. Z. Jacobson, W. G. Colella, D. M. Golden, Science 2005, 308, 1901;d) X. Yang, Y. Wang, C. M. Li, D. Wang, Nano Res. 2021, 14, 3446;e) Y. Yang, Y. Yang, Y. Liu, S. Zhao, Z. Tang, Small Sci. 2021, 1, 2100015;f) S. Zhao, C. Tan, C.‐T. He, P. An, F. Xie, S. Jiang, Y. Zhu, K.‐H. Wu, B. Zhang, H. Li, J. Zhang, Y. Chen, S. Liu, J. Dong, Z. Tang, Nat. Energy 2020, 5, 881;g) S. Zhao, Y. Yang, Z. Tang, Angew. Chem. 2022, 134, e202110186.a) L. Tian, X. Zhai, X. Wang, X. Pang, J. Li, Z. Li, Electrochim. Acta 2020, 337, 135823;b) N. C. S. Selvam, L. Du, B. Y. Xia, P. J. Yoo, B. You, Adv. Funct. Mater. 2021, 31, 2008190;c) S. Xu, H. Zhao, T. Li, J. Liang, S. Lu, G. Chen, S. Gao, A. M. Asiri, Q. Wu, X. Sun, J. Mater. Chem. A 2020, 8, 19729;d) X. Zheng, P. Li, S. Dou, W. Sun, H. Pan, D. Wang, Y. Li, Energy Environ. Sci. 2021, 14, 2809;e) X. Zheng, B. Li, Q. Wang, D. Wang, Y. Li, Nano Res. 2022, https://doi.org/10.1007/s12274-022-4429-9.a) S. Fukuzumi, Y. M. Lee, W. Nam, ChemSusChem 2017, 10, 4264;b) V. Kumaravel, A. Abdel‐Wahab, Energy Fuels 2018, 32, 6423;c) J. Zhang, W. Hu, S. Cao, L. Piao, Nano Res. 2020, 13, 2313.a) S. Satyapal, J. Petrovic, C. Read, G. Thomas, G. Ordaz, Catal. Today 2007, 120, 246;b) J. Yang, A. Sudik, C. Wolverton, D. J. Siegel, Chem. Soc. Rev. 2010, 39, 656;c) S. Jiang, H. Suo, T. Zhang, C. Liao, Y. Wang, Q. Zhao, W. Lai, Catalysts 2022, 12, 123.D. T. Tran, T. Kshetri, D. C. Nguyen, J. Gautam, V. H. Hoa, H. T. Le, N. H. Kim, J. H. Lee, Nano Today 2018, 22, 100.a) F.‐Y. Chen, Z.‐Y. Wu, Z. Adler, H. Wang, Joule 2021, 5, 1704;b) L. A. King, M. A. Hubert, C. Capuano, J. Manco, N. Danilovic, E. Valle, T. R. Hellstern, K. Ayers, T. F. Jaramillo, Nat. Nanotechnol. 2019, 14, 1071;c) P. Lettenmeier, R. Wang, R. Abouatallah, S. Helmly, T. Morawietz, R. Hiesgen, S. Kolb, F. Burggraf, J. Kallo, A. S. Gago, Electrochim. Acta 2016, 210, 502.a) M. W. Kanan, D. G. Nocera, Science 2008, 321, 1072;b) J. Park, H. Kim, K. Jin, B. J. Lee, Y.‐S. Park, H. Kim, I. Park, K. D. Yang, H.‐Y. Jeong, J. Kim, J. Am. Chem. Soc. 2014, 136, 4201;c) J. S. Kim, I. Park, E. S. Jeong, K. Jin, W. M. Seong, G. Yoon, H. Kim, B. Kim, K. T. Nam, K. Kang, Adv. Mater. 2017, 29, 1606893;d) H. Kim, J. Park, I. Park, K. Jin, S. E. Jerng, S. H. Kim, K. T. Nam, K. Kang, Nat. Commun. 2015, 6, 8253.J. S. Kim, B. Kim, H. Kim, K. Kang, Adv. Energy Mater. 2018, 8, 1702774.a) D. A. Corrigan, J. Electrochem. Soc. 1987, 134, 377;b) R. Singh, J. Pandey, N. Singh, B. Lal, P. Chartier, J.‐F. Koenig, Electrochim. Acta 2000, 45, 1911.a) Y. C. Lin, Z. Q. Tian, L. J. Zhang, J. Y. Ma, Z. Jiang, B. J. Deibert, R. X. Ge, L. Chen, Nat. Commun. 2019, 10, 162;b) Y. H. Wang, S. Y. Hao, X. N. Liu, Q. Q. Wang, Z. W. Su, L. C. Lei, X. W. Zhang, ACS Appl. Mater. Interfaces 2020, 12, 37006;c) F. Lv, J. R. Feng, K. Wang, Z. P. Dou, W. Y. Zhang, J. H. Zhou, C. Yang, M. C. Luo, Y. Yang, Y. J. Li, P. Gao, S. J. Guo, ACS Cent. Sci. 2018, 4, 1244;d) Z. Li, S. Wang, Y. Y. Tian, B. H. Li, H. J. Yan, S. Zhang, Z. M. Liu, Q. J. Zhang, Y. C. Lin, L. Chen, Chem. Commun. 2020, 56, 1749;e) R. X. Ge, L. Li, J. W. Su, Y. C. Lin, Z. Q. Tian, L. Chen, Adv. Energy Mater. 2019, 9, 1901313.f) S. R. Ede, Z. P. Luo, J. Mater. Chem. A 2021, 9, 20131.a) B. Cui, H. Lin, J. B. Li, X. Li, J. Yang, J. Tao, Adv. Funct. Mater. 2008, 18, 1440;b) S. Chen, S.‐Z. Qiao, ACS Nano 2013, 7, 10190.I. Nikolov, R. Darkaoui, E. Zhecheva, R. Stoyanova, N. Dimitrov, T. Vitanov, J. Electroanal. Chem. 1997, 429, 157.a) J. Wang, S.‐J. Kim, J. Liu, Y. Gao, S. Choi, J. Han, H. Shin, S. Jo, J. Kim, F. Ciucci, Nat. Catal. 2021, 4, 212;b) Y. Li, X. Du, J. Huang, C. Wu, Y. Sun, G. Zou, C. Yang, J. Xiong, Small 2019, 15, 1901980.J. Zhou, L. Zhang, Y.‐C. Huang, C.‐L. Dong, H.‐J. Lin, C.‐T. Chen, L. Tjeng, Z. Hu, Nat. Commun. 2020, 11, 1984.a) D. Xu, M. B. Stevens, Y. Rui, G. DeLuca, S. W. Boettcher, E. Reichmanis, Y. Li, Q. Zhang, H. Wang, Electrochim. Acta 2018, 265, 10;b) N. Zhang, X. Feng, D. Rao, X. Deng, L. Cai, B. Qiu, R. Long, Y. Xiong, Y. Lu, Y. Chai, Nat. Commun. 2020, 11, 4066;c) B. Zhang, K. Jiang, H. Wang, S. Hu, Nano Lett. 2018, 19, 530.H. Jiang, Q. He, Y. Zhang, L. Song, Acc. Chem. Res. 2018, 51, 2968.M. Wang, Y. Wang, S. S. Mao, S. Shen, Nano Energy 2021, 88, 106216.J. Chen, F. Zheng, S.‐J. Zhang, A. Fisher, Y. Zhou, Z. Wang, Y. Li, B.‐B. Xu, J.‐T. Li, S.‐G. Sun, ACS Catal. 2018, 8, 11342.K. Liu, C. Zhang, Y. Sun, G. Zhang, X. Shen, F. Zou, H. Zhang, Z. Wu, E. C. Wegener, C. J. Taubert, J. T. Miller, Z. Peng, Y. Zhu, ACS Nano 2018, 12, 158.Z. Lu, H. Wang, D. Kong, K. Yan, P.‐C. Hsu, G. Zheng, H. Yao, Z. Liang, X. Sun, Y. Cui, Nat. Commun. 2020, 11, 4354.a) N. Nitta, F. Wu, J. T. Lee, G. Yushin, Mater. Today 2015, 18, 252;b) J.‐Z. Kong, F. Zhou, C.‐B. Wang, X.‐Y. Yang, H.‐F. Zhai, H. Li, J.‐X. Li, Z. Tang, S.‐Q. Zhang, J. Alloys Compd. 2013, 554, 221;c) Y.‐S. Lee, D. Ahn, Y.‐H. Cho, T. E. Hong, J. Cho, J. Electrochem. Soc. 2011, 158, A1354;d) J.‐Z. Kong, H.‐F. Zhai, C. Ren, G.‐A. Tai, X.‐Y. Yang, F. Zhou, H. Li, J.‐X. Li, Z. Tang, J. Solid State Electrochem. 2013, 18, 181;e) S. W. Lee, C. Carlton, M. Risch, Y. Surendranath, S. Chen, S. Furutsuki, A. Yamada, D. G. Nocera, Y. Shao‐Horn, J. Am. Chem. Soc. 2012, 134, 16959.a) N. Colligan, V. Augustyn, A. Manthiram, J. Phys. Chem. C 2015, 119, 2335;b) X. Zheng, J. Yang, Z. Xu, Q. Wang, J. Wu, E. Zhang, S. Dou, W. Sun, D. Wang, Y. Li, Angew. Chem., Int. Ed. 2022, n/a, e202205946.J. Wang, L. Li, H. Tian, Y. Zhang, X. Che, G. Li, ACS Appl. Mater. Interfaces 2017, 9, 7100.a) X. Zhang, L. An, J. Yin, P. Xi, Z. Zheng, Y. Du, Sci. Rep. 2017, 7, 43590;b) F. Yang, K. Sliozberg, I. Sinev, H. Antoni, A. Bähr, K. Ollegott, W. Xia, J. Masa, W. Grünert, B. R. Cuenya, W. Schuhmann, M. Muhler, ChemSusChem 2017, 10, 156;c) C. Dong, X. Yuan, X. Wang, X. Liu, W. Dong, R. Wang, Y. Duan, F. Huang, J. Mater. Chem. A 2016, 4, 11292;d) C. Tang, H.‐S. Wang, H.‐F. Wang, Q. Zhang, G.‐L. Tian, J.‐Q. Nie, F. Wei, Adv. Mater. 2015, 27, 4516;e) H. Huang, C. Yu, C. Zhao, X. Han, J. Yang, Z. Liu, S. Li, M. Zhang, J. Qiu, Nano Energy 2017, 34, 472;f) W. Ma, R. Ma, C. Wang, J. Liang, X. Liu, K. Zhou, T. Sasaki, ACS Nano 2015, 9, 1977.a) J.‐S. Li, L.‐X. Kong, Z. Wu, S. Zhang, X.‐Y. Yang, J.‐Q. Sha, G.‐D. Liu, Carbon 2019, 145, 694;b) Y. Pan, K. Sun, S. Liu, X. Cao, K. Wu, W.‐C. Cheong, Z. Chen, Y. Wang, Y. Li, Y. Liu, D. Wang, Q. Peng, C. Chen, Y. Li, J. Am. Chem. Soc. 2018, 140, 2610;c) C.‐C. Hou, S. Cao, W.‐F. Fu, Y. Chen, ACS Appl. Mater. Interfaces 2015, 7, 28412;d) J. Wang, W. Yang, J. Liu, J. Mater. Chem. A 2016, 4, 4686;e) L. Yu, Y. Xiao, C. Luan, J. Yang, H. Qiao, Y. Wang, X. Zhang, X. Dai, Y. Yang, H. Zhao, ACS Appl. Mater. Interfaces 2019, 11, 6890;f) Y. Wang, T. Williams, T. Gengenbach, B. Kong, D. Zhao, H. Wang, C. Selomulya, Nanoscale 2017, 9, 17349;g) L. Yan, L. Cao, P. Dai, X. Gu, D. Liu, L. Li, Y. Wang, X. Zhao, Adv. Funct. Mater. 2017, 27, 1703455.a) F. Cao, X. Yang, C. Shen, X. Li, J. Wang, G. Qin, S. Li, X. Pang, G. Li, J. Mater. Chem. A 2020, 8, 7245;b) P. Jiang, Y. Yang, R. Shi, G. Xia, J. Chen, J. Su, Q. Chen, J. Mater. Chem. A 2017, 5, 5475;c) Q. Kang, D. Lai, W. Tang, Q. Lu, F. Gao, Chem. Sci. 2021, 12, 3818.d) K. Huang, B. Zhang, J. Wu, T. Zhang, D. Peng, X. Cao, Z. Zhang, Z. Li, Y. Huang, J. Mater. Chem. A 2020, 8, 11938.S. Gottesfeld, S. Srinivasan, J. Electroanal. Chem. Interfacial Electrochem. 1978, 86, 89.a) V. I. Birss, A. Damjanovic, P. Hudson, J. Electrochem. Soc. 1986, 133, 1621.b) B. E. Conway, T. Liu, Langmuir 1990, 6, 268.I. Hamidah, S. Sriyono, M. N. Hudha, Indones. J. Sci. Technol. 2020, 5, 34.a) B. M. Hunter, H. B. Gray, A. M. Muller, Chem. Rev. 2016, 116, 14120;b) C. Hu, L. Zhang, J. Gong, Nat. Rev. Chem. 2017, 1, 0003;c) J. Song, C. Wei, Z.‐F. Huang, C. Liu, L. Zeng, X. Wang, Z. J. Xu, Chem. Soc. Rev. 2020, 49, 2196;d) F. Song, L. Bai, A. Moysiadou, S. Lee, C. Hu, L. Liardet, X. Hu, J. Am. Chem. Soc. 2018, 140, 7748;e) N.‐T. Suen, S.‐F. Hung, Q. Quan, N. Zhang, Y.‐J. Xu, H. M. Chen, Chem. Soc. Rev. 2017, 46, 337.N. Zhang, Y. Chai, Energy Environ. Sci. 2021, 14, 4647.Y. Sun, H. Liao, J. Wang, B. Chen, S. Sun, S. J. H. Ong, S. Xi, C. Diao, Y. Du, J.‐O. Wang, M. B. H. Breese, S. Li, H. Zhang, Z. J. Xu, Nat. Catal. 2020, 3, 554.a) J. H. Montoya, L. C. Seitz, P. Chakthranont, A. Vojvodic, T. F. Jaramillo, J. K. Nørskov, Nat. Mater. 2017, 16, 70;b) I. C. Man, H. Y. Su, F. Calle‐Vallejo, H. A. Hansen, J. I. Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. K. Nørskov, J. Rossmeisl, ChemCatChem 2011, 3, 1159;c) L. C. Seitz, C. F. Dickens, K. Nishio, Y. Hikita, J. Montoya, A. Doyle, C. Kirk, A. Vojvodic, H. Y. Hwang, J. K. Norskov, T. F. Jaramillo, Science 2016, 353, 1011;d) J. K. Nørskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J. R. Kitchin, T. Bligaard, H. Jonsson, J. Phys. Chem. B 2004, 108, 17886;e) J. Rossmeisl, A. Logadottir, J. K. Nørskov, Chem. Phys. 2005, 319, 178.a) D. A. Kuznetsov, M. A. Naeem, P. V. Kumar, P. M. Abdala, A. Fedorov, C. R. Müller, J. Am. Chem. Soc. 2020, 142, 7883;b) X. Rong, J. Parolin, A. M. Kolpak, ACS Catal. 2016, 6, 1153.a) J. T. Mefford, X. Rong, A. M. Abakumov, W. G. Hardin, S. Dai, A. M. Kolpak, K. P. Johnston, K. J. Stevenson, Nat. Commun. 2016, 7, 11053;b) A. Grimaud, W. T. Hong, Y. Shao‐Horn, J.‐M. Tarascon, Nat. Mater. 2016, 15, 121;c) A. Grimaud, O. Diaz‐Morales, B. Han, W. T. Hong, Y.‐L. Lee, L. Giordano, K. A. Stoerzinger, M. T. Koper, Y. Shao‐Horn, Nat. Chem. 2017, 9, 457;d) Y. Yan, J. Lin, J. Cao, S. Guo, X. Zheng, J. Feng, J. Qi, J. Mater. Chem. A 2019, 7, 24486;e) X. Cheng, E. Fabbri, Y. Yamashita, I. E. Castelli, B. Kim, M. Uchida, R. Haumont, I. Puente‐Orench, T. J. Schmidt, ACS Catal. 2018, 8, 9567.a) C. Z. Yuan, H. B. Wu, Y. Xie, X. W. Lou, Angew. Chem., Int. Ed. 2014, 53, 1488;b) M. Hamdani, R. N. Singh, P. Chartier, Int. J. Electrochem. Sci. 2010, 5, 556;c) L. F. Hu, L. M. Wu, M. Y. Liao, X. H. Hu, X. S. Fang, Adv. Funct. Mater. 2012, 22, 998;d) I. Katsounaros, S. Cherevko, A. R. Zeradjanin, K. J. J. Mayrhofer, Angew. Chem., Int. Ed. 2014, 53, 102;e) R. Kotz, S. Stucki, Electrochim. Acta 1986, 31, 1311;f) X. B. Zheng, Y. P. Chen, X. S. Zheng, C. Q. Zhao, K. Rui, P. Li, X. Xu, Z. X. Cheng, S. X. Dou, W. P. Sun, Adv. Energy Mater. 2019, 9, 1803482.a) F. Calle‐Vallejo, M. T. Koper, A. S. Bandarenka, Chem. Soc. Rev. 2013, 42, 5210;b) I. E. Stephens, A. S. Bondarenko, F. J. Perez‐Alonso, F. Calle‐Vallejo, L. Bech, T. P. Johansson, A. K. Jepsen, R. Frydendal, B. P. Knudsen, J. Rossmeisl, J. Am. Chem. Soc. 2011, 133, 5485;c) T. Bligaard, J. K. Nørskov, Electrochim. Acta 2007, 52, 5512;d) Z. Xu, J. R. Kitchin, J. Chem. Phys. 2015, 142, 104703;e) J. R. Kitchin, J. K. Nørskov, M. A. Barteau, J. Chen, Phys. Rev. Lett. 2004, 93, 156801.M. Grisolia, J. Varignon, G. Sanchez‐Santolino, A. Arora, S. Valencia, M. Varela, R. Abrudan, E. Weschke, E. Schierle, J. Rault, Nat. Phys. 2016, 12, 484.a) C. J. Ballhausen, H. B. Gray, Inorg. Chem. 1962, 1, 111.b) T. A. Betley, Q. Wu, T. Van Voorhis, D. G. Nocera, lnorg. Chem. 2008, 47, 1849.a) X. Li, Z. Cheng, X. Wang, Electrochem. Energy Rev. 2021, 4, 136;b) J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. J. S. Shao‐Horn, Science 2011, 334, 1383.C. Wei, Z. Feng, G. G. Scherer, J. Barber, Y. Shao‐Horn, Z. J. Xu, Adv. Mater. 2017, 29, 1606800.A. Houmam, Chem. Rev. 2008, 108, 2180.J. Li, D. Chu, H. Dong, D. R. Baker, R. Jiang, J. Am. Chem. Soc. 2020, 142, 50.E. Hu, X. Yu, R. Lin, X. Bi, J. Lu, S. Bak, K.‐W. Nam, H. L. Xin, C. Jaye, D. A. Fischer, K. Amine, X.‐Q. Yang, Nat. Energy 2018, 3, 690.S. Zhou, X. Miao, X. Zhao, C. Ma, Y. Qiu, Z. Hu, J. Zhao, L. Shi, J. Zeng, Nat. Commun. 2016, 7, 11510.Y. Duan, S. Sun, S. Xi, X. Ren, Y. Zhou, G. Zhang, H. Yang, Y. Du, Z. J. Xu, Chem. Mater. 2017, 29, 10534.T. Maiyalagan, K. A. Jarvis, S. Therese, P. J. Ferreira, A. Manthiram, Nat. Commun. 2014, 5, 3949.a) B. Han, D. Qian, M. Risch, H. Chen, M. Chi, Y. S. Meng, Y. Shao‐Horn, J. Phys. Chem. Lett. 2015, 6, 1357;b) F. Calle‐Vallejo, N. G. Inoglu, H.‐Y. Su, J. I. Martinez, I. C. Man, M. T. Koper, J. R. Kitchin, J. Rossmeisl, Chem. Sci. 2013, 4, 1245.Y. Li, P. Hasin, Y. Wu, Adv. Mater. 2010, 22, 1926.J. Haenen, W. Visscher, E. Barendrecht, J. Electroanal. Chem. Interfacial Electrochem. 1986, 208, 273.H. Wang, J. Wu, A. Dolocan, Y. Li, X. Lü, N. Wu, K. Park, S. Xin, M. Lei, W. Yang, J. B. Goodenough, Proc. Natl. Acad. Sci. U. S. A. 2019, 116, 23473.Y. Zhu, W. Zhou, Y. Chen, J. Yu, M. Liu, Z. Shao, Adv. Mater. 2015, 27, 7150.J. Qin, V. P. Pasko, M. G. McHarg, H. C. Stenbaek‐Nielsen, Nat. Commun. 2014, 5, 3740.a) J. Li, C. Shu, C. Liu, X. Chen, A. Hu, J. Long, Small 2020, 16, 2001812;b) J. Peng, Y. Yuan, W. Yuan, K. Peng, Int. J. Hydrogen Energy 2021, 46, 24117;c) J. Qi, T. Xu, J. Cao, S. Guo, Z. Zhong, J. Feng, Nanoscale 2020, 12, 6204;d) Z.‐h. Xiao, D.‐c. Jiang, H. Xu, J.‐t. Zhou, Q.‐z. Zhang, P.‐w. Du, Z.‐l. Luo, C. Gao, Chin. J. Chem. Phys. 2018, 31, 691;e) H. Yang, H. Sun, X. Fan, X. Wang, Q. Yang, X. Lai, Mater. Chem. Front. 2021, 5, 259;f) X. Li, Y. Sun, F. Ren, Y. Bai, Z. Cheng, Mater. Today Energy. 2021, 19, 100619.g) K. Zhang, G. Zhang, J. Qu, H. Liu, Small 2018, 14, 1802760.a) D. Chen, M. Qiao, Y. R. Lu, L. Hao, D. Liu, C. L. Dong, Y. Li, S. Wang, Angew. Chem., Int. Ed. 2018, 57, 8691;b) L. Pan, S. Wang, W. Mi, J. Song, J.‐J. Zou, L. Wang, X. Zhang, Nano Energy 2014, 9, 71;c) S. Wang, L. Pan, J.‐J. Song, W. Mi, J.‐J. Zou, L. Wang, X. Zhang, J. Am. Chem. Soc. 2015, 137, 2975.H. N. Nong, T. Reier, H.‐S. Oh, M. Gliech, P. Paciok, T. H. T. Vu, D. Teschner, M. Heggen, V. Petkov, R. Schlögl, Nat. Catal. 2018, 1, 841.T. Ling, D.‐Y. Yan, Y. Jiao, H. Wang, Y. Zheng, X. Zheng, J. Mao, X.‐W. Du, Z. Hu, M. Jaroniec, Nat. Commun. 2016, 7, 12876.P. W. Menezes, A. Indra, A. Bergmann, P. Chernev, C. Walter, H. Dau, P. Strasser, M. Driess, J. Mater. Chem. A 2016, 4, 10014.a) X. Ren, C. Wei, Y. Sun, X. Liu, F. Meng, X. Meng, S. Sun, S. Xi, Y. Du, Z. Bi, G. Shang, A. C. Fisher, L. Gu, Z. J. Xu, Adv. Mater. 2020, 32, 2001292;b) S. Sun, Y. Sun, Y. Zhou, S. Xi, X. Ren, B. Huang, H. Liao, L. P. Wang, Y. Du, Z. J. Xu, Angew. Chem. 2019, 131, 6103.X. Zheng, Y. Chen, W. Lai, P. Li, C. Ye, N. Liu, S. X. Dou, H. Pan, W. Sun, Adv. Funct. Mater. 2022, 32, 2200663.D. Huang, J. Yu, Z. Zhang, C. Engtrakul, A. Burrell, M. Zhou, H. Luo, R. C. Tenent, ACS Appl. Mater. Interfaces 2020, 12, 10496.Y. Liu, H. Wang, D. Lin, C. Liu, P.‐C. Hsu, W. Liu, W. Chen, Y. Cui, Energy Environ. Sci. 2015, 8, 1719.J. Hwang, R. R. Rao, L. Giordano, Y. Katayama, Y. Yu, Y. Shao‐Horn, Science 2017, 358, 751.J. Suntivich, W. T. Hong, Y.‐L. Lee, J. M. Rondinelli, W. Yang, J. B. Goodenough, B. Dabrowski, J. W. Freeland, Y. Shao‐Horn, J. Phys. Chem. C 2014, 118, 1856.N. Zhang, C. Wang, J. Chen, C. Hu, J. Ma, X. Deng, B. Qiu, L. Cai, Y. Xiong, Y. Chai, ACS Nano 2021, 15, 8537.X. Zheng, Y. Chen, X. Zheng, G. Zhao, K. Rui, P. Li, X. Xu, Z. Cheng, S. X. Dou, W. Sun, Adv. Energy Mater. 2019, 9, 1803482.M. Sathiya, G. Rousse, K. Ramesha, C. P. Laisa, H. Vezin, M. T. Sougrati, M. L. Doublet, D. Foix, D. Gonbeau, W. Walker, A. S. Prakash, M. Ben Hassine, L. Dupont, J. M. Tarascon, Nat. Mater. 2013, 12, 827.W.‐K. Han, J.‐X. Wei, K. Xiao, T. Ouyang, X. Peng, S. Zhao, Z.‐Q. Liu, Angew. Chem., Int. Ed. 2022, e202206050.Z. Lu, H. Wang, D. Kong, K. Yan, P.‐C. Hsu, G. Zheng, H. Yao, Z. Liang, X. Sun, Y. Cui, Nat. Commun. 2014, 5, 4345.a) K. J. Lee, B. D. McCarthy, J. L. Dempsey, Chem. Soc. Rev. 2019, 48, 2927;b) A. Sivanantham, P. Ganesan, A. Vinu, S. Shanmugam, ACS Catal. 2019, 10, 463.a) Z. Lu, K. Jiang, G. Chen, H. Wang, Y. Cui, Adv. Mater. 2018, 30, 1800978;b) K. Mizushima, P. Jones, P. Wiseman, J. B. Goodenough, Mater. Res. Bull. 1980, 15, 783.G. P. Gardner, Y. B. Go, D. M. Robinson, P. F. Smith, J. Hadermann, A. Abakumov, M. Greenblatt, G. C. Dismukes, Angew. Chem., Int. Ed. 2012, 51, 1616.G. Gardner, J. Al‐Sharab, N. Danilovic, Y. B. Go, K. Ayers, M. Greenblatt, G. Charles Dismukes, Energy Environ. Sci. 2016, 9, 184.G. P. Gardner, Y. B. Go, D. M. Robinson, P. F. Smith, J. Hadermann, A. Abakumov, M. Greenblatt, G. C. Dismukes, Angew. Chem., Int. Ed. Engl. 2012, 51, 1616.Z. Lu, G. Chen, Y. Li, H. Wang, J. Xie, L. Liao, C. Liu, Y. Liu, T. Wu, Y. Li, A. C. Luntz, M. Bajdich, Y. Cui, J. Am. Chem. Soc. 2017, 139, 6270.J. Wang, S.‐J. Kim, J. Liu, Y. Gao, S. Choi, J. Han, H. Shin, S. Jo, J. Kim, F. Ciucci, H. Kim, Q. Li, W. Yang, X. Long, S. Yang, S.‐P. Cho, K. H. Chae, M. G. Kim, H. Kim, J. Lim, Nat. Catal. 2021, 4, 212.C. Yang, G. Rousse, K. L. Svane, P. E. Pearce, A. M. Abakumov, M. Deschamps, G. Cibin, A. V. Chadwick, D. A. D. Corte, H. A. Hansen, T. Vegge, J. M. Tarascon, A. Grimaud, Nat. Commun. 2020, 11, 1378.X. Zheng, P. Cui, Y. Qian, G. Zhao, X. Zheng, X. Xu, Z. Cheng, Y. Liu, S. X. Dou, W. Sun, Angew. Chem., Int. Ed. Engl. 2020, 59, 14533.J. Wang, L. Li, H. Tian, Y. Zhang, X. Che, G. Li, ACS Appl. Mater. Interfaces 2017, 9, 7100.a) R. Gummow, D. Liles, M. Thackeray, Mater. Res. Bull. 1993, 28, 235;b) R. Gummow, M. Thackeray, W. David, S. Hull, Mater. Res. Bull. 1992, 27, 327.Z. Chen, J. Wang, D. Chao, T. Baikie, L. Bai, S. Chen, Y. Zhao, T. C. Sum, J. Lin, Z. Shen, Sci. Rep. 2016, 6, 25771.a) X. Zhang, W. J. Jiang, A. Mauger, Qilu, F. Gendron, C. M. Julien, J. Power Sources 2010, 195, 1292;b) D. Wang, X. Li, Z. Wang, H. Guo, Y. Xu, Y. Fan, J. Ru, Electrochim. Acta 2016, 188, 48.D. Qian, Y. Hinuma, H. Chen, L. S. Du, K. J. Carroll, G. Ceder, C. P. Grey, Y. S. Meng, J. Am. Chem. Soc. 2012, 134, 6096.a) A. Grimaud, K. J. May, C. E. Carlton, Y. L. Lee, M. Risch, W. T. Hong, J. Zhou, Y. Shao‐Horn, Nat. Commun. 2013, 4, 2439;b) J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. Shao‐Horn, Science 2011, 334, 1383;c) B. J. Kim, E. Fabbri, D. F. Abbott, X. Cheng, A. H. Clark, M. Nachtegaal, M. Borlaf, I. E. Castelli, T. Graule, T. J. Schmidt, J. Am. Chem. Soc. 2019, 141, 5231;d) F. Calle‐Vallejo, O. A. Díaz‐Morales, M. J. Kolb, M. T. M. Koper, ACS Catal. 2015, 5, 869.J. Gao, C.‐Q. Xu, S.‐F. Hung, W. Liu, W. Cai, Z. Zeng, C. Jia, H. M. Chen, H. Xiao, J. Li, J. Am. Chem. Soc. 2019, 141, 3014.a) F. Wang, Y. Han, C. S. Lim, Y. Lu, J. Wang, J. Xu, H. Chen, C. Zhang, M. Hong, X. Liu, Nature 2010, 463, 1061;b) X. Feng, D. C. Sayle, Z. L. Wang, M. S. Paras, B. Santora, A. C. Sutorik, T. X. Sayle, Y. Yang, Y. Ding, X. Wang, Y. S. Her, Science 2006, 312, 1504.a) M. Guilmard, J. Power Sources 2003, 115, 305;b) A. Gupta, W. D. Chemelewski, C. Buddie Mullins, J. B. Goodenough, Adv. Mater. 2015, 27, 6063.G. Gardner, J. Al‐Sharab, N. Danilovic, Y. B. Go, K. Ayers, M. Greenblatt, G. C. Dismukes, Energy Environ. Sci. 2016, 9, 184.a) B. S. Yeo, A. T. Bell, J. Phys. Chem. C 2012, 116, 8394;b) Y. Gorlin, C. J. Chung, J. D. Benck, D. Nordlund, L. Seitz, T. C. Weng, D. Sokaras, B. M. Clemens, T. F. Jaramillo, J. Am. Chem. Soc. 2014, 136, 4920;c) G. Zhao, P. Li, N. Cheng, S. X. Dou, W. Sun, Adv. Mater. 2020, 32, 2000872;d) R. Subbaraman, D. Tripkovic, D. Strmcnik, K. C. Chang, M. Uchimura, A. P. Paulikas, V. Stamenkovic, N. M. Markovic, Science 2011, 334, 1256;e) H. Tang, J. Wei, F. Liu, B. Qiao, X. Pan, L. Li, J. Liu, J. Wang, T. Zhang, J. Am. Chem. Soc. 2016, 138, 56.a) Y. Yang, X. Su, L. Zhang, P. Kerns, L. Achola, V. Hayes, R. Quardokus, S. L. Suib, J. J. C. He, ChemCatChem 2019, 11, 1689;b) J. S. Hong, H. Seo, Y. H. Lee, K. H. Cho, C. Ko, S. Park, K. T. Nam, Small Methods 2020, 4, 1900733;c) C. Meng, Y.‐F. Gao, X.‐M. Chen, Y.‐X. Li, M.‐C. Lin, Y. Zhou, ACS Sustainable Chem. Eng. 2019, 7, 18055;d) W. Gou, M. Zhang, Y. Zou, X. Zhou, Y. Qu, ChemCatChem 2019, 11, 6008.a) H. Shi, G. Zhao, J. Phys. Chem. C 2014, 118, 25939;b) T. W. Kim, M. A. Woo, M. Regis, K.‐S. Choi, J. Phys. Chem. Lett. 2014, 5, 2370;c) X. Liu, Z. Chang, L. Luo, T. Xu, X. Lei, J. Liu, X. Sun, Chem. Mater. 2014, 26, 1889;d) J. Zhang, D. Zhang, Y. Yang, J. Ma, S. Cui, Y. Li, B. Yuan, RSC Adv. 2016, 6, 92699;e) J. Landon, E. Demeter, N. İnoğlu, C. Keturakis, I. E. Wachs, R. Vasić, A. I. Frenkel, J. R. Kitchin, ACS Catal. 2012, 2, 1793;f) A. Indra, P. W. Menezes, N. R. Sahraie, A. Bergmann, C. Das, M. Tallarida, D. Schmeißer, P. Strasser, M. Driess, J. Am. Chem. Soc. 2014, 136, 17530;g) G. Karkera, T. Sarkar, M. D. Bharadwaj, A. S. Prakash, ChemCatChem 2017, 9, 3681.X. Zheng, P. Cui, Y. Qian, G. Zhao, X. Zheng, X. Xu, Z. Cheng, Y. Liu, S. X. Dou, W. Sun, Angew. Chem. 2020, 132, 14641.J. W. D. Ng, M. García‐Melchor, M. Bajdich, P. Chakthranont, C. Kirk, A. Vojvodic, T. F. Jaramillo, Nat. Energy 2016, 1, 16053.Z. R. Zhang, C. X. Liu, C. Feng, P. F. Gao, Y. L. Liu, F. N. Ren, Y. F. Zhu, C. Cao, W. S. Yan, R. Si, S. M. Zhou, J. Zeng, Nano Lett. 2019, 19, 8774.J. Shan, Y. Zheng, B. Shi, K. Davey, S.‐Z. Qiao, ACS Energy Lett. 2019, 4, 2719.a) N. Zhang, X. Feng, D. Rao, X. Deng, L. Cai, B. Qiu, R. Long, Y. Xiong, Y. Lu, Y. Chai, Nat. Commun. 2020, 11, 4066;b) E. Fabbri, D. F. Abbott, M. Nachtegaal, T. J. Schmidt, Curr. Opin. Electrochem. 2017, 5, 20;c) D. Guan, G. Ryu, Z. Hu, J. Zhou, C. L. Dong, Y. C. Huang, K. Zhang, Y. Zhong, A. C. Komarek, M. Zhu, X. Wu, C. W. Pao, C. K. Chang, H. J. Lin, C. T. Chen, W. Zhou, Z. Shao, Nat. Commun. 2020, 11, 3376;d) C. Walter, P. W. Menezes, S. Orthmann, J. Schuch, P. Connor, B. Kaiser, M. Lerch, M. Driess, Angew. Chem., Int. Ed. Engl. 2018, 57, 698;e) C. W. Song, H. Suh, J. Bak, H. B. Bae, S.‐Y. Chung, Chem 2019, 5, 3243;f) Y. Zhou, N. López, ACS Catal. 2020, 10, 6254;g) C. Lee, K. Shin, C. Jung, P.‐P. Choi, G. Henkelman, H. M. Lee, ACS Catal. 2019, 10, 562.H. Wang, S. Xu, C. Tsai, Y. Li, C. Liu, J. Zhao, Y. Liu, H. Yuan, F. Abild‐Pedersen, F. B. Prinz, Science 2016, 354, 1031.A. Grimaud, A. Demortière, M. Saubanère, W. Dachraoui, M. Duchamp, M.‐L. Doublet, J.‐M. Tarascon, Nat. Energy 2016, 2, 16189.T. M. Anderson, R. Cao, E. Slonkina, B. Hedman, K. O. Hodgson, K. I. Hardcastle, W. A. Neiwert, S. Wu, M. L. Kirk, S. Knottenbelt, E. C. Depperman, B. Keita, L. Nadjo, D. G. Musaev, K. Morokuma, C. L. Hill, J. Am. Chem. Soc. 2005, 127, 11948.M. N. Grisolia, J. Varignon, G. Sanchez‐Santolino, A. Arora, S. Valencia, M. Varela, R. Abrudan, E. Weschke, E. Schierle, J. E. Rault, J. P. Rueff, A. Barthélémy, J. Santamaria, M. Bibes, Nat. Phys. 2016, 12, 484.A. R. Zeradjanin, J. Masa, I. Spanos, R. Schlogl, Front. Energy Res. 2021, 8, 613092.C. Peng, H. Liu, J. Chen, Y. Zhang, L. Zhu, Q. Wu, W. Zou, J. Wang, Z. Fu, Y. Lu, Appl. Surf. Sci. 2021, 544, 148897.X. Zheng, Y. Chen, X. Zheng, G. Zhao, K. Rui, P. Li, X. Xu, Z. Cheng, S. X. Dou, W. Sun, Adv. Energy Mater. 2019, 9, 1803482.Y. Deng, B. S. Yeo, ACS Catal. 2017, 7, 7873.D. Wang, J. Zhou, Y. Hu, J. Yang, N. Han, Y. Li, T.‐K. Sham, J. Phys. Chem. C 2015, 119, 19573.K. A. Stoerzinger, W. T. Hong, E. J. Crumlin, H. Bluhm, Y. Shao‐Horn, Acc. Chem. Res. 2015, 48, 2976.J. Y. C. Chen, L. Dang, H. Liang, W. Bi, J. B. Gerken, S. Jin, E. E. Alp, S. S. Stahl, J. Am. Chem. Soc. 2015, 137, 15090.J. Gao, C.‐Q. Xu, S.‐F. Hung, W. Liu, W. Cai, Z. Zeng, C. Jia, H. M. Chen, H. Xiao, J. Li, Y. Huang, B. Liu, J. Am. Chem. Soc. 2019, 141, 3014.K. Zhu, X. Zhu, W. Yang, Angew. Chem., Int. Ed. 2019, 58, 1252. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Advanced Energy Materials Wiley

Lightest Metal Leads to Big Change: Lithium‐Mediated Metal Oxides for Oxygen Evolution Reaction

Download PDF
24 pages

Loading next page...
 
/lp/wiley/lightest-metal-leads-to-big-change-lithium-mediated-metal-oxides-for-iKTMGnSzw2
Publisher
Wiley
Copyright
© 2022 Wiley‐VCH GmbH
ISSN
1614-6832
eISSN
1614-6840
DOI
10.1002/aenm.202201934
Publisher site
See Article on Publisher Site

Abstract

IntroductionThere is a global race to phase out the use of fossil fuels, with expectations of reducing emissions and the large amounts of environmentally polluting by‐products. Clean energy technologies, therefore, have received massive attention for the purpose of addressing global climate issues.[1] Owing to the abundance and carbon‐free nature of water sources, water electrolysis is becoming one of the most sustainable energy technologies.[2] On the one hand, water electrolysis is able to produce renewable hydrogen energy, which is promising to replace the conventional fossil fuels.[3] On the other hand, water splitting is usually based on the oxygen evolution reaction (OER), which synergistically limits the whole efficiency of water electrolysis due to its sluggish kinetics.[4] The multiple electron/proton exchange reactions of the OER have thus become a key challenge in water splitting. In order to improve the overall efficiency of water, many effective electrocatalysts have been investigated for improvement of the slow kinetics of the OER.To date, metal oxides (MOs) have shown outstanding electrocatalytic capability in water oxidation.[5] In particular, Ru/Ir‐based metal oxides have demonstrated a high catalytic activity and excellent durability of OER at an acidic proton exchange membrane (PEM) electrolyzer, but their high cost and resource scarcity requires developments of alternative catalysts with high cost‐effectiveness.[6] Therefore, a large number of studies have focused on layered hydroxides, chalcogenide oxides, spinel oxides, and amorphous Co‐based oxides.[7] Among these, bimetallic oxides (M1‐O‐M2) generally show higher electrical conductivity and catalytic activity than unmodified monometallic oxides.[8] These results indicate a close correlation between the electronic structure of the catalyst and the catalytic performance. Typically, M1‐O‐M2 type catalysts are originally prepared by occasional doping/substitution of exotic metals.[9] The exotic metals change the lattice parameters of the catalyst as well as the overlap between atomic orbitals.[10] 3d transition metals are by far the most widely used bimetallic oxides in OER processes. These metal ions typically have unsaturated coordination sites. These attractive structures have outstanding electron transfer rates and meanwhile, can serve as intermediate adsorption and activity centers for the OER.[11] Nikolov et al. have systematically investigated the M1‐O‐M2 effects. Through control of different elemental doping, the OER catalytic activities were tailored, resulting in a sequence of Co3O4 < NixCo3−xO4 < CuxCo3−xO4 < LixCo3−xO4.[12] In addition, structures with M1‐O‐M2 are likely to experience surface reconstruction due to the leaching effects, thereby generating dynamic remodeling to form the true active centers of the OER.[13] The introduction of M1 cations into M1‐O‐M2 oxides effectively changes the oxidation state of M2. For instance, some investigations have suggested that metal ions with high oxidation states usually indicate the presence of more active centers for the OER.[14] Moreover, by elaborate design of structure, the M1 cation can be removed during the activation of electrochemical process to re‐build a more dynamic surface toward the OER.[15] This irreversible reconstruction process was also believed to offer more benefits for the OER. These include effective changes in the local electronic structure, metal‐oxygen covalency, and hydrophilicity of the catalyst.[13b,16] In turn, these effects improve the adsorption and desorption capacity and the activation capacity of catalyst intermediates, which afterward determine their OER activity.[2b,13b,16]Lithium metal oxides (LMOs), well known as cathodes in lithium ion batteries, are now being extended to application as OER electrocatalysts due to their remarkable catalytic reactivity and following benefits: 1) compared to the previously reported OER catalysts, such as commercial IrO2[27] and RuO2.[17] transition metal alloy,[17,26] hydroxides[18,24] and phosphides,[19,25] LMOs show a highly concentrated high‐activity area with a low overpotential and a fast turn‐over efficiency (Figure 1a); 2) LMOs have been commercialized for many years due to the fast development of lithium ion batteries, thus LMOs are easy to scale up from either new production or recycled LMOs from battery wastes; and 3) LMOs catalysts are able to precisely quantify the chemical valence of transition metals through control the amount of lithium, thus tuning surface structures. Among the various M‐O‐M oxides, Li‐O‐M structures have shown unique chemical and physical features (Figure 1b). The insertion and extraction of lithium ions, synchronized with the valence changes of metals in LMOs, enable a novel controllable surface.[20] This structural reconstruction affects the local electronic structure and subsequently exposes the real active centers for the OER. This function finally tailors the molecular interactions involved in water oxidation.[21] In particular, the special layered structure of LMO can be exfoliated, forming single/few‐layer LMO. These properties intensively increase the number of active sites, resulting in an improved catalytic capability. In recent studies, more LMO electrocatalysts have been developed with different crystal structures (layered, spinel, etc.) formed by combining lithium with other noble or transition metals.[20,22] With deeper analysis and characterization, investigations on LMO have been quickly increasing to further improve the OER efficiency. This research includes dopant strategies, controlled removal of Li, and surface modifications.[20,23] This review summarizes recent advances in LMO materials for the OER. First, we briefly describe two different catalytic mechanisms for the OER (the adsorbate evolution mechanism [AEM] and the lattice oxygen mechanism [LOM]). We then outline the principles of bimetallic oxide modification in terms of electronic states, vacancies, bonding, lattice oxygen activation, surface reconstruction, and electrical conductivity. After that, we give a general overview of the historical development as well as the classification of LMOs, and describe specifically three methods of chemical modification of LMOs, focusing on dynamic surface reconstruction, the formation of lattice oxygen, and the valence evolution of active metal centers during the OER. Finally, we provide a perspective on the current challenges and future prospects of LMOs. We anticipate that this review will provide a comprehensive reference for the design of OER electrocatalysts and the development of polymetallic oxides.1Figurea) Catalytic activity comparison of typical OER catalysts and LMOs in aspects of overpotential and Tafel slope of transition metal LDHs,[24] transition metal phosphides,[19,25] transition metal alloys,[17,26] RuO2,[17] IrO2,[27] and lithium metal oxides at 10 mA cm−2. b) The overall clue of this review to understand LMO catalysts.General OER PathwaysThe OER typically involves four proton/electron coupling processes to produce molecular oxygen.[28] Under acidic conditions, two water molecules (H2O) are oxidized to produce four protons (H+) and one oxygen molecule (O2) (Equation (1)),[28b] while hydroxyl (OH−) groups act as oxygen sources in alkaline electrolytes (Equation (2)).[28a]In acidic solution, the total reaction formula for the OER is:12H2O=O2+4H++4e−\[\begin{array}{*{20}{c}}{2{{\rm{H}}_2}{\rm{O}} = {{\rm{O}}_2} + 4{{\rm{H}}^ + } + 4{{\rm{e}}^ - }}\end{array}\]In alkaline solution, the total reaction formula for the OER is:24OH−=O2+2H2O+4e−\[\begin{array}{*{20}{c}}{4{\rm{O}}{{\rm{H}}^ - } = {{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}} + 4{{\rm{e}}^ - }}\end{array}\]In this work, A bibliometric analysis[29] has been used to visually map the development of OER catalysts by selecting more than 5000 articles from the related topic area with titles, keywords, and abstracts in Web of Science (Figure 2a). The visualization mapping result indicates that various OER catalysts and different mechanisms have been proposed for the OER over the years, but it is generally accepted that there are two ways to understand the physicochemical processes of the OER: the AEM and the LOM (Figure 2b). It is worth noting that the lithium indicates a high occurrence in metal‐oxide‐based OER catalysts, suggesting its importance in the development of efficient water oxidation (Figure 2c). The AEM consists of four proton‐coupled electron transfer processes centered on metal ions, and oxygen is mainly derived from adsorbed water molecules.[30] With an AEM pathway, the reactant bodies, such as H2O and OH− groups, provide electrons and form an intermediate to release oxygen during the reaction. Specifically, water molecules pass through a single‐electron oxidation process and thus are adsorbed on the oxygen‐ligand metal (M) site of the electrocatalyst, forming an adsorbed *OH (step 1) (Figure 3a).[2b]2Figurea) Visualization map of OER catalyst network, b) keywords of different mechanisms, and c) the role of lithium in metal‐oxide‐based OER catalysts.3Figurea) Diagram of the AEM process. Reproduced with permission.[31] Copyright 2021, Royal Society of Chemistry. b) Reaction mechanism diagram of AEM and LOM on energy bands. Reproduced with permission.[32] Copyright 2020, Springer Nature. c–e) Schematic diagram of the LOM with three different mechanisms (oxygen vacancy site mechanism, single metal site mechanism, and dual metal site mechanism). Reproduced with permission.[31] Copyright 2021, Royal Society of Chemistry.The *OH is then oxidized to *O, followed by the formation of an *OOH intermediate through the adsorption of another water molecule (step 3). Finally, the *OOH adsorbed on the M site is oxidized, releasing oxygen, and the initially clean M site can be recovered (step 4). The stepwise process of the AEM presumably provides a way to distinguish the origins of the different catalyst activities. Typically, the ideal oxygen intermediate should be neither too strong nor too weak.[33] The catalyst surface in the conventional AEM mechanism is relatively stable, since only the metal center undergoes a valence change during the intermediate evolution of oxygen. For some catalysts, the AEM has been the commonly accepted mechanism and successfully helped to explain the OER pathway by illustrating the energy differences of intermediates. For some oxygen‐containing catalysts, more investigations have raised the question whether the lattice oxygen also participates in the reaction and forms O2. This mechanism, focusing on the different oxygen intermediate products, is called the LOM.[33a,34] It is notable that some oxygen‐containing catalysts can also work in the AEM process. For instance, when the energy position of the d‐band of the M in metal oxides is higher than the O p‐band, the metal sites mostly act as adsorption sites and active centers. This is because electrons from the p‐band are transferred to the d‐band. This change is able to produce ligand holes and thus facilitate the formation of oxygen‐containing species.[2b] In this way, the OER occurs on the surface of a metal site rather than on lattice oxygen, which fulfills the conditions for the AEM pathway. When a catalyst works in the opposite way, however, the OER follows the LOM mechanism (Figure 3b).[32] In the newly proposed LOM mechanism, the evolution of oxygen results in a change in its surface, where the OH−/H2O species will bind at the oxygen vacancies and be used as lattice oxygen for cycling.[31] Activation of the lattice oxygen is therefore a requirement for the successful triggering of the LOM pathway, which requires a catalyst host with LOM favorable structure. There are three main pathways for the LOM, depending on the different active centers of the catalyst.[15b,35] Activated lattice oxygen can act as a reaction center, which is referred to as the “oxygen vacancy mechanism”. Figure 3c depicts how OH− is adsorbed to form H2O directly. After the generation of O2, O vacancies are finally refilled by OH−. The cycling of this process continuously enables high efficiency in the OER. Alternatively, some catalysts allows direct coupling of *OO to lattice oxygen through surface deconstruction and subsequent deprotonation (Figure 3d).[35a,d] In addition to a single active center, some researchers have used a bimetallic site mechanism to explain the LOM.[35b] As shown in Figure 3e, coupling of adjacent active lattice oxygen can form M‐OO‐M, where the *OO* group that is formed usually acts as a peroxide.[15b]These conclusions mean that the OER pathway could be controllable through adjusting the electronic structures of catalysts. For example, the lattice oxygen is limited by the lower energy level of the oxygen p‐band center, or by the lower oxygen activity than the metal cation, so that the OER reaction is mainly by the AEM pathway.[32] In contrast, by escalating the central energy of oxygen close to the cationic d‐band of metals, the LOM may be triggered to free more lattice oxygen.Key Features of M1‐O‐M2 for OERSo far, MOs are one of the most effective kinds of OER catalysts because of their specific properties, which make them highly valuable for research on the electrolysis of water. The introduction of an extra metal has been reported as an effective strategy to bring about changes in the local electronic structure and thus enhance intrinsic properties by increasing electrical conductivity, creating vacancies, optimizing the morphology, and surface reconstruction.[10f,36] Interestingly, significant performance improvements have been further obtained by using bimetallic oxides (M1‐O‐M2) rather than monometallic catalysts. These improvements exist because the dopant effects of metals inevitably change the average or local lattice parameters, thus changing the overlap between atomic orbitals and leading to electron transfer.[10,37] For instance, the introduction of element A in AxByOz type catalysts could escalate the valence of the B metal to a high oxidation state, resulting in high TM‐O covalency, where TM stands for transition metal. This change thereby increases the rate of electron transfer.[14,38] Besides these considerations, ligand effects and strain effects of dual metal oxides have also been considered as reasons for the impact on their electrocatalytic activity toward the OER.[8,31] In this section, we systematically introduce representative key features of M1‐O‐M2 type catalysts. These features have been proved as important reasons that could directly affect the OER process. These key properties include electronic states, vacancies, bonds, lattice oxygen activation, surface reconstruction, and electrical conductivity.Electronic StateOrbital OccupancyIn general, the eg orbitals of transition metal ions in metal oxides are related to the σ‐bonding of anionic adsorbates.[39] The filling of eg orbitals can affect not only the binding of oxygen intermediates on the active metal sites, but also the local coordination geometry of the catalyst, which, in turn, can change the OER performance of the catalyst.[39b,40] The eg orbital filling of transition metal cations can usually change the OER performance, where the lower the filling rate of eg orbitals, the stronger the binding of intermediates to the oxide surface.[30c] In chalcogenide oxides, the rate determining step (RDS) is the process in which OOH adsorbates on the transition metal cation sites form OO bonds, and when the filling of eg orbitals approaches unity, the rate determining step (RDS) can be greatly promoted, resulting in the highest OER activity.[40b] In addition, in some spinel oxides, too little eg orbital electron filling (eg < 1) can limit the deprotonation step of M‐OOH−, but too much eg orbital electron filling (eg > 1) can limit the formation of OO bonds in M‐OOH−. The right balance between the rate‐limiting steps is obtained when the filling of eg orbitals is approximately equal to 1.[41] Usually, electron‐transfer initiated bond formation and dissociation in reactions, thus electron occupancy on the cracked orbitals, such as the t2g and eg orbital, is very important.[42] By adjusting the valence of transition metal oxides, the electron filling number on both eg and t2g orbitals can be changed. For example, the valence‐shift of Ni ions from +2 to +3 in spinel oxides NiCo2O4 can cause an electron loss eg orbital to create an electron vacancy (Figure 4a). As a result, the creation of vacant sites can optimize the adsorption energy barrier of intermediates, enhancing its OER performance.[43] Similarly, it has been reported that the orbital positions in LMOs can also be varied through the oxidation and reduction of transition metals (Figure 4b). For instance, the loss of electrons of the Ni, Co, and Mn ions in Li1.2Ni0.15Co0.1Mn0.55O2 reduce the electron occupancy in the eg orbital or in the t2g orbitals, producing not fully filled orbitals (Figure 4c).[44] The valence change of the typical bimetallic oxides mostly relies on the increase of voltage, which is difficult to precisely tune. Nevertheless, it is more controllable for LMOs to vary the chemical valence of the transition metal ions owing to the adjustable amount of lithium‐extractions.4Figurea) eg orbital occupancy of Ni in NiCo2O4. Reproduced with permission.[43] Copyright 2019, American Chemical Society; b,c) Redox couple evolution of Li1.2Ni0.15Co0.1Mn0.55O2 during cycling. Reproduced with permission.[44] Copyright 2018, Springer Nature.Spin StateIn general, increasing the spin state of transition metals can optimize the electronic configuration toward a better OER.[30c] Zeng et al. reported that the shift of Co3+ ions from the low spin state to the high spin state can increase the OER activity. This control is achieved by doping La atoms into cobalt oxides.[45] Interestingly, when the composition of LaCoO3 is further optimized to LaCo0.9Fe0.1O3 by introducing Fe (Figure 5a–c), the OER performance continues to improve through the enhancement of the CoO covalency.[46] Delithiation has also appeared as another strategy to change the spin status of transition metals.[47] For instance, delithiated Li1−xCoO2 promotes low spin Co3+ ions to Co4+ or medium spin Co3+ ions. This alteration can subsequently increase the OER performance. Also, Han et al. reported that the tips of LiCoO2 nanorods have higher OER activity, because the low‐spin Co3+ is mainly distributed on the sides, while the tips are mainly high‐ or medium‐spin Co3+.[48]5Figurea) Total density of states (TDOS) of Co ions in the low spin state in LaCoO3, and Co ions in the high spin state in LaCo0.9 Fe0.1O3. The insets represent the relationship between projected density of states (PDOS) and EF of LaCoO3 and LaCo0.9Fe0.1O3 from −1.5 to 1.5 V. b) Co d state and O p state PDOS in LaCoO3 and LaCo0.9Fe0.1O3, c) schematic diagram of Co 3d–O 2p overlap in LaCoO3 and LaCo0.9Fe0.1O3. Reproduced with permission.[46] Copyright 2017, American Chemical Society. d) Cyclic voltammograms of Co3O4, LT‐LiCoO2 and HT‐LiCoO2. e) Mechanism of OER on LT‐LiCoO2, and the qualitative one‐electron energy diagram of Li1−xCoO2. Reproduced with permission.[47] Copyright 2014, Macmillan Publishers Limited.Valence StateAccording to the principle of electroneutrality, interactions between elements can regulate the valence of transition metals. Transition metal oxides are usually active toward the OER because of their various oxidation states, their ability to adsorb intermediate products, and their easy participation in redox reactions.[30c] For example, the substitution of Ni on Co sites in spinel NixCo3−xO4 nanowires can increase the rate of electron exchange due to the higher oxidation status of the metals.[49] Some investigations have also suggested that tetravalent cations tend to be the active sites for the OER.[12,50] For instance, Na+ ion vacancies in this material resulted in more Co4+ centers in the CoO2 units of layered Na0.67CoO2 catalysts, which could shorten the OO length.[51] The short OO bonds facilitate the coupling between two adjacent metal‐oxygen O−O− interactions to form peroxide ions, without the need to generate oxygen by the conventional pathway (generation of OOH− species). During the OER process, the removal of Li will cause the change of the valence of transition metal ions (Figure 5d,e).[47] Lu et al. used electrochemical lithiation to tune the electronic structure of their catalyst by successively extracting lithium ions from LiCoO2 and converting the material to Li0.5CoO2 in organic electrolytes.[20] The presence of Co ions in the highly oxidized state increases its hydrophilicity toward oxygen species, resulting in easy binding to OH ions to form OOH, thus improving the OER performance. Zhu et al. prepared LiCo0.8Fe0.2O2 by using iron (Fe) doping.[52] The synergistic effect originating from the bimetallic structure raised the oxidation state of the cobalt.[52] In sum, a high oxidation state enables fewer electrons in the d‐orbitals, which directly determines the spin state and eg electron number.[53]VacanciesVacancies strongly affect the surface charge distribution of the catalysts.[35d,54] Attempts have been made to modify the structure of catalysts by introducing cationic vacancies.[55] For instance, Sn vacancies generated on SnCo0.9Fe0.1(OH)6 effectively increase the distribution of active sites and thus facilitate electron migration as well as the adsorption of reactants.[55a] SnCo0.9Fe0.1(OH)6 samples with Sn vacancies thus promote an increased OER performance over the initial sample. Strasser et al. prepared a unique porous NiIrO catalyst, where the leaching of nickel from NiIrO creates vacancies.[56] The presence of vacancies can shorten the IrO bonds and further enhance the catalyst performance. In addition, Qiao and co‐workers reported that the introduction of oxygen vacancies into CoO can effectively tune its electronic structure to enhance charge transfer and optimize the OER activity (Figure 6a,b).[57] As another example, researchers confirmed that the leaching out of Zn from ZnCo2O4 generates vacancies during the OER process, which activates the surface of the catalyst and increases the hydroxylation rate.[58] The OER performance of ZnCo2O4 was significantly higher than that of Co3O4. More results have indicated that ZnCo2O4 has more Co3+ than Co3O4 after the OER.[58] It has been confirmed that these Co3+ ions are the real active sites for the OER.[58] Vacancies in LMOs, including lithium and oxygen vacancy, also play an effective role in regulating electronic structures of the catalysts. For instance, lithium vacancies created in de‐lithiumed LiNiO2 lead to a larger charge deviation of the oxygen ligand and subsequently cause heterostructured interfaces of NiOOH species on the surface of LMOs. The reconstructed surface is able to stabilize the newly formed NiOO* intermediates, allowing an efficient and durable OER process (Figure 6c).[59] Layered LiCoO2 with abundant defects, including Co vacancies and oxygen vacancies, on the surface due to the exfoliation process. These generated defects usually enable more d‐band electron vacancies and enhance CoO covalency. The presence of Co vacancies can effectively improve the adsorption of intermediates, thus reducing the energy potential barrier for the rate‐determining step of OER.[60] By reducing the thickness, ultrathin LiCoO2 has an increased number of oxygen vacancies, which significantly enhances the OER kinetics due to the enriched d‐band holes. By introducing Li vacancies in LiNi0.5Co0.2Mn0.3O2, the transition metal ions can be oxidized to higher oxidation states, which significantly improves the oxidation performance.[61]6Figurea) Atomic configurations of O2 molecules. b) Estimated density of states on an original CoO surface and a CoO surface with O vacancies. Reproduced with permission.[57] Copyright 2016, Springer Nature. c) The schematic diagram of the evolution of LiNiO2. Reproduced with permission.[59a] Copyright 2020, Wiley‐VCH. d) Schematic illustration of the electrochemical tuning process of LiMPO4/rGO. Reproduced with permission.[62] Copyright 2015, Royal Society of Chemistry.BondsCovalent Metal‐Oxygen BondsIn general, the covalency of the metal‐oxygen bond is determined by the charge transfer energy (the energy difference between the unoccupied metal 3d center and the occupied O 2p center).[63] In metal oxides, the covalent mixing between the octahedrally coordinated metal cation and the oxygen anion can affect the exchange rate of neighboring ions.[30c] As discussed, M1‐O‐M2 structures lead to a redistribution of the electron density between the metal and the oxygen. Substitution with a metal that is more electronegative than the initial metal decreases the energy of the d‐band, leading to an enhancement of the M‐O covalency. Besides this, metal vacancies can also change the average (or local) chemical valence of the metal ions, which reduces the energy of the d‐band and enlarges the metal‐oxygen covalency. It has been recently reported that enhancing the CoO covalency by adding cationic vacancies can promote the OER activity of spinel oxides.[30c] Some researchers have shown that 10–30 at% Fe substitution can promote the covalency of CoO. In addition, the orbital hybridization and metal‐oxygen bond covalency of La (Mn, Fe, Co, Ni)O3 is related to the 3D electron distribution in the metal center.[64] In addition, it was observed from Y2−xSrxRu2O7 catalysts that the substitution of Sr2+ introduces vacancies into the lattice oxygen, which promotes RuO covalency and thus enhances the activity.[65] Electron energy band rearrangement can reduce the charge transfer energy and alter the interface charge‐transfer kinetics. Zheng et al. doped Mg into LiCoO2 materials to change the electronic structure of Co,[66] which synergistically enhanced the CoO covalency. Lithium mediated cobalt oxide (LiCoO2) can also promote CoO bonds to the fully covalent state,[20] thus reducing the energy gap between the metal 3d orbitals and the O 2p orbitals. This change promotes the OER activity. More lithiated materials, such as LiNi0.75Fe0.25PO4/rGO hybrid catalyst, where rGO is reduced graphene oxide, have also proved their enhanced OER performance (Figure 6d).[62] All these investigations are associated with a change in the transition metal valence and an increase in covalency between the metal and the oxygen.Distorted Lattice‐Oxygen NetworksDespite the oxygen vacancies, the de‐embedding of Li in layered LMOs materials triggers the lattice oxygen redox chemistry of OER.[14] The main reason is the oxygen network is severely distorted during de‐lithiation, forming peroxide‐like/superoxide species at the very end of the charge, eventually presenting short OO.[67] The short OO bonds facilitate the coupling between two adjacent metal‐oxygen OO interactions to form peroxide ions and enable a LOM pathway, instead of a conventional AEM pathway, which needs the generation of OOH* species.[51] The two metal sites on the bimetallic oxide undergo deprotonation, producing two oxygen species that combine to form an OO bond.[35b] In general, the lattice and electronic structure of materials can affect bonding, such as the bond length, bond angle and atomic distance. These features can affect the reaction path and the exchange of adjacent ions. In addition, exchange interactions between ions are influenced by wave function overlap. The longer the distance between protons (bond length), the less wave function overlap there is (Figure 7a).[51] The hole‐activated oxygen ligands can also become electrophilic, which will promote the formation of OO bonds and eventually enhance the OER activity of the catalyst.[59a] For instance, LiNiO2 generates Li1−xNiO2/g‐NiOOH during electrochemistry, with the formation of oxygen vacancies (Figure 7b). The oxygen vacancies can be filled by the massive migration of lattice oxygen. These active lattice oxygen can potentially trigger the generation of Ni4+, which can promote the deprotonation during OER,[68] leading to charge compensation effects by electron holes. These uncompensated electron holes on the oxygen atoms, thus, act as electrophilic centers to enhance the OER activity.[59a,14]7Figurea) The OO bonds shorter than 2.4 to 2.5 Å are highlighted with thick red lines. Reproduced with permission.[51] Copyright 2019, National Academy of Sciences. b) The OER process of LiNiO2. Reproduced with permission.[59a] Copyright 2020, Wiley‐VCH. c) Schematic of the electrochemical LMOs. Reproduced with permission.[69] Copyright 2014, Macmillan Publishers Limited. d) Schematic of Ru‐Co/LiCoO2. Reproduced with permission.[22b] Copyright 2022, Wiley‐VCH.Surface ReconstructionReconstruction usually refers to the surface changes of the electrocatalyst from its original morphology in terms of structure, components, and crystallinity during the actual reaction.[13b] Under strong oxidation conditions, most electrocatalysts undergo significant changes in their physicochemical properties (i.e., chemical composition and physical structure) of the surface during the OER.[2b,70] This change leads to a new surface reconfiguration. During the electrocatalyst reconstruction process, the change in components leads to the formation of new chemical bonds. These new chemical bonds finally alter the electronic features, as discussed above, leading to a strong improvement in the OER. Lithium ion de‐embedding during OER is a unique property of LMO materials. Usually, the lithium ion de‐embedding is accompanied by surface reconstruction during the charging process (Figure 7c). It is shown that both LT‐LiCoO2 and HT‐LiCoO2 undergo surface reconstruction in the first cycle of OER, producing Co3O4, which may be the active species for the reaction.[22a]Electrical ConductivityElectrical conductivity is an important indicator of catalyst efficiency. Excellent electrical conductivity requires an increase in the charge transfer rate and charge density, with electrons and holes determining whether there is good or bad conductivity. The rate of reaction in the OER and the electrical conductivity affect each other, and the rate of reaction can also affect the rate of charge transfer to the active sites on the catalyst surface. Many atoms in metal oxides exchange charge through orbital hybridization. M 3d and O 2p orbitals overlap with the strong electron part of the separated domain, which is commonly believed to result in high conductivity.[40a] Zhu et al. effectively enhanced the conductivity of LiCoO2 by introducing Fe. The coupling effect between iron and cobalt substantially increased its charge transfer rate.[52] In addition, the cationic coordination strategy allows us to control the local coordination and thus optimize the electronic structure of the catalyst. By doping Ru atoms in layered LiCoO2, there is a strong electronic coupling between the ruthenium and cobalt sites, which increase the electron conductivity of the catalyst (Figure 7d). The enhanced electron density can substantially optimize the binding energy and accelerate oxygen precipitation kinetics.[22b] In sum, the mobility of lithium works like “Dominoes”, leading to changes in various aspects, including electron re‐arrangements, oxygen activation, surface reconstruction and electronic conductivity. Understanding the structural uniqueness of LMOs rather than other metal oxides is very important to further optimize the OER performance of this class of catalysts (Figure 8).8FigureStructural features of LMOs and typical metal oxides.Emergence of Lithium Metal OxidesHistory of LMOAs discussed, M1‐O‐M2 type catalysts are a very important branch of the metal oxide family. The unique structural feasibility of M1‐O‐M2 structures as efficient OER catalysts has also been proved due to their optimized electronic structures. Li‐O‐M, as one of the M1‐O‐M2 oxides, has received massive attention due to its outstanding OER capability. As a typical cathode in lithium‐ion batteries, the electronic structure of LMO can be tuned by lithium intercalation and extraction, making it an intensively investigated OER catalyst (Figure 9).[71] In 2012, these researchers found that Li2Co2O4 consists of cubic Co4O4, while LiCoO2 consists of alternating layers of CoO and LiO octahedra.[72] In 2014, a de‐lithiated LiCoO2 (De‐LiCoO2) catalyst was first prepared through an electrochemical process to escalate the potential to a high level.[69] Compared with the original LiCoO2, De‐LiCoO2 has a lower overpotential and more significant catalytic properties. In addition, they introduced a variety of other transition metals into the pristine LiCoO2 and also obtained high OER catalytic activity. The unique electronic structure after delithiation is the key factor for the enhanced OER performance. In 2016, Gardner et al. found that partial delamination of unstable Li+ from layered LiCoO2 triggers surface reconstruction of LiCo2O4. Spinel and cubic lithium cobalt oxides retain the same cubic space group based on the [Co4O4]n+ cubic subunit, providing a lower Co4+ oxidation potential and lower cubic carbon pore mobility.[73] In contrast, the layered LiCoO2 has some problems with surface hole delocalization, which affects the synergistic facilitation of the electrons and holes in terms of entropy. Many previous studies have found that layered LiCoO2 is inert toward OER catalysis, and its catalytic activity is weaker than that of its spinel counterpart.[66,74] Lu et al., however, used electrochemical delithiation (De‐LCO) to enhance the active surface of layered LiCoO2 (LCO).[75] It was found that the more stable surfaces usually show little effect on their performance due to lithium content, while the more active surfaces are usually more dependent on lithium extraction. The extraction of lithium can increase the Co4+ sites and change the 2p state of active oxygen. Recently, Wang et al. adjusted the dynamic surface reorganization of layered LiCoO2 by precisely controlling the in situ catalyst leaching.[76] In the OER process, chlorine (Cl) dopant reduces the electrochemical potential of layered LiCoO2, thereby triggering in situ oxidation and delithiation of Co. In addition, the researchers successfully achieved the goal of preparing LMOs with high catalytic activity by controlling their morphology, doping, and electrochemical delithiation. These results indicate that LMOs have remarkable catalytic properties and are promising for applications in OER electrocatalysis.9FigureA timeline of major developments in lithium metal oxides. Reproduced with permission.[73] Copyright 2012, Wiley‐VCH; Reproduced with permission.[70] Copyright 2014, Macmillan Publishers Limited; Reproduced with permission.[62] Copyright 2015, Royal Society of Chemistry; Reproduced with permission.[52] Copyright 2015, Wiley‐VCH; Reproduced with permission.[80] Copyright 2017, American Chemical Society; Reproduced with permission.[76] Copyright 2017, American Chemical Society; Reproduced with permission.[66] Copyright 2019, Wiley‐VCH; Reproduced with permission.[79] Copyright 2020, Wiley‐VCH; Reproduced with permission.[78] Copyright 2020, Springer Nature; Reproduced with permission.[77] Copyright 2021, Springer Nature.LMO FamiliesA number of LMOs has been developed for use in high‐performance OER processes. Figure 10a summarizes all the elements that have been used for designing Li‐O‐M structures. Furthermore, LMO catalysts have also used as an efficient substrate to form LMO‐based composite or modified LMO (Figure 10b). These catalysts include: LMO with different phases, metal/non‐metal doped LMO, and LMO‐based heterostructures. The diversity of compositions and structures of LMOs provides design flexibility for the preparation of excellent OER catalysts.10Figurea) Elemental distribution of LMO families. b) Classification of LMO phases and composites, including: LMO,[23,61,72,77] metal/non‐metal doped LMO,[52,66,76] and LMO‐based heterostructure.[62,78] Reproduced with permission.[73] Copyright 2012, Wiley‐VCH; Reproduced with permission.[23] Copyright 2017, American Chemical Society; Reproduced with permission.[61] Copyright 2020, American Chemical Society; Reproduced with permission.[78] Copyright 2020, Springer Nature. Reproduced with permission.[52] Copyright 2015, Wiley‐VCH; Reproduced with permission.[66] Copyright 2019, Wiley‐VCH; Reproduced with permission.[77] Copyright 2021, Springer Nature. Reproduced with permission.[62] Copyright 2015, Royal Society of Chemistry; Reproduced with permission.[79] Copyright 2020, Wiley‐VCH.LMOLiCoO2 is the most classic LMO for the OER and is usually available in two different structures: layered LiCoO2 (HT‐LiCoO2) formed at high temperatures (800 °C) and spinel structured LiCoO2 (LT‐LiCoO2) formed at low temperatures (400 °C). Li+ occupies 16c octahedral sites of LT‐LiCoO2, and Co3+ occupies 16d octahedral sites of the spinel skeleton.[80] Studies have shown that LT‐LiCoO2 is composed of cubic Co4O4 units, while HT‐LiCoO2 consists of LiCo3O4 units.[47] The OER performance results indicate that the catalytic activity of layered HT‐LiCoO2 is not as good as that of LT‐LiCoO2, although they share the same OER mechanisms. The reason why LT‐LiCoO2 has better OER performance is because LT‐LiCoO2 offers easier surface reconstruction to form the real active centers.[22a] Similar to LiCoO2, LiNi0.5Co0.2Mn0.3O2 (NCM523) forms a spinel structure at low temperatures, which also shows promising OER activity.[81] In addition, it has been reported that the synergistic effects between Ni and Li can produce more defects on the surface, leading to a disordered but more active structure.[82] Huang et al. successfully synthesized three different structures of NCM523, named low‐temperature synthetic spinel NCM (LT‐NCM), high‐temperature synthetic lithium‐deficient disordered NCM (DO‐NCM) and high‐temperature layered hexagonal NCM (HT‐NCM) (Figure 11a).[62] DO‐NCM shows remarkable catalytic efficiency with a low onset potential of 1.48 V by shifting the valence of Ni2+ to Ni3+ through introducing lithium deficiency.11Figurea) Crystal structures of HT‐NCM, DO‐NCM, and LT‐NCM. Reproduced with permission.[61] Copyright 2020, American Chemical Society. b) Schematic diagram of LiCoO2‐NS, where NS stands for nanosheet. c) Atomic force microscope (AFM) image of LiCoO2‐NS. d) Electronic structure of LiCoO2‐NS. Reproduced with permission.[79] Copyright 2017, American Chemical Society.On decreasing the dimensions of LMO to ultra‐thin LMO nanosheets, oxygen vacancies and high‐spin Co4+ are generated, which can enhance oxygen adsorption (Figure 11b–d).[79] The overpotential of ultra‐thin LiCoO2 nanosheets is 0.41 V at 10 mA cm−2. Optimization of the morphologies of LMO can always trigger some interesting physical phenomena. For instance, researchers developed LiCoO2 nanorods to study the OER activity in alkaline solution.[48a] One of the interesting results that they found is that low‐index crystalline surfaces are formed in the sides while the tips mainly have surfaces with high‐index crystallinity. This phenomenon causes low‐spin Co3+ to be predominant on the lateral surface, while high‐spin or medium‐spin Co3+ forms at the tips.[48a–83] Investigations have shown that enhancement of TM‐O bond covalency can significantly improve the kinetics of the OER, but it is also accompanied by surface instability.[77,84] Yang et al. reported a solid electrocatalyst, α‐Li2IrO3, which reacts with water to form a birnessite phase during oxidation/delithiation (Figure 12a,b) and presents an overpotential of 290 mV at 10 mA cm−2.[77] Similarly, Gao et al. developed amorphous LiIrOx by doping lithium ions into iridium oxide,[85] which showed remarkable stability and activity toward the OER in acidic media (270 mV at 10 mA cm−2). The K ions in KOH solution are introduced into the catalyst structure during the electrolysis, in turn promoting the oxidation of water (Figure 12c). In addition to its remarkable stability, this solid electrocatalyst has indicated an effective strategy to improve OER catalytic activity. In this way, the conflict between the OER performance and stability of the catalyst is balanced.12Figurea) Structural model of Li1/3Ir2/3O2 layer. b) Schematic diagram of chemical oxidation of water by charge compensation. c) The connection between the battery system and the water system. Reproduced with permission.[77] Copyright 2020, Springer Nature. d) DFT optimized atomic structures of LiCoO1.8Cl0.2. e) Schematic diagram of the in situ surface reconstruction processes of LiCoO1.8Cl0.2. Reproduced with permission.[76] Copyright 2021, Springer Nature.Metal/Non‐Metal Doped LMODoping is another effective strategy to further improve the OER activity of LMO. The addition of other ions can tune the electronic structure of LMO, which impacts the binding energy of OER intermediates, the conductivity and the capability for electron‐transfer.[86] Doping with some nonmetallic ions has been reported as an effective strategy to improve the performance of the OER.[76] For instance, doping with Cl reduces the electrochemical potential of layered LiCoO2, thereby triggering in situ oxidation and delithiation of Co (Figure 12d,e).[76] This structure (LiCoO1.8Cl0.2) achieved an overpotential of 302 mV at a current density of 50 mA cm−2geo. In addition to anions, some metal cation doping can also effectively change the electronic structure of catalysts. Fe is often used as a dopant due to its abundant reserves and non‐polluting characteristics. For example, Fe doped LiCoO2 shows a unique synergistic coupling effect between Fe and Co,[53] resulting in an optimized electronic structure of Co with an increased rate of charge transfer. At the current density of 10 mA cm−2, the Fe‐doped LiCoO2 achieved an overpotential of 0.34 V with current density of 10 mA cm−2, showing better catalytic performance than a commercial IrO2 sample. In some reports. Al doped lithium nickel oxides were also fabricated, such as LiNi1−xAlxO2. This strategy is effective to suppress the mixing of Ni2+ in the Li+ layer but obtain a higher concentration of Ni3+. This has been considered as a key role to achieve excellent and stable OER activity.[87] Zheng et al. proposed a mechanical shear‐assisted exfoliation strategy to synthesize defect‐abundant atomic‐layered LiCoO2 (AD‐LCO).[60] Microscopic characterizations confirm the successfully fabricated defective LiCoO2 nanosheets (Figure 13a–d). Benefiting from the unique structural superiority, the obtained AD‐LCO exhibited superior OER activity and stability. In another work, combining doping engineering and shear‐force‐assisted exfoliation strategies, they developed a novel 2D Mg doped LiCoO2 (ELCMO) for oxygen electrocatalysis for the first time (Figure 13e).[66] Microscopic characterizations indicated the successful exfoliation of LiCoO2 from its bulk form to nanosheet morphology with a well‐maintained crystal structure. The synthesized ELCMO exhibited remarkable catalytic performance with an overpotential of only 329 mV at a current density of 10 mA cm−2 in 1 m KOH (Figure 13f). In this work, Mg dopant was believed to alter the electronic structure, which led to the enhanced Co 3d–O 2p covalency and hybridization (Figure 13g). Furthermore, the insertion and extraction of lithium ions from metal oxides is the other important feature that can improve the electronic structure and increase catalytic efficiency.[88]13FigureStructural and chemical characterizations of AD‐LCO. a) High‐resolution transmission electron microscope (HRTEM) image. b,c) High‐angle annular dark‐field‐scanning transmission electron microscope (HAADF‐STEM) images. d) Strain mapping of (c) Reproduced with permission.[60] Copyright 2022, Wiley‐VCH. Schematic illustration of the fabrication process for ELCMO. e) Illustration of fabrication process of ELCMO. f) LSV curves of ELCMO and reference samples. g) Qualitative one‐electron energy diagram. Reproduced with permission.[66] Copyright 2019, Wiley‐VCH.Similarly, the synergistic effects originating from extra Zn2+ dopant and Li+ in the spinel ZnCo2O4 resulted in charge deviation of the oxygen ligand and greater CoO covalency, owing to the charge compensation from transferring the oxygen charge to the octahedral Co center.[59b] Sun et al. reported another spinel Li0.5Zn0.5Fe0.125Co1.875O4, which showed excellent OER performance. This was achieved by promoting oxygen charge transfer to the active transition metal center through the co‐dopant method.[59b] In conclusion, the addition of Li ions and extra metal dopants can change the valence state of the original metal oxide or create vacancies, leading to stronger M‐O covalency.LMO‐Based HeterostructureHeterostructures, such as metal/metal (hydrogen) oxide systems, featuring strong electronic and geometric effects between metal and support, exhibit great advantages for enhancing catalytic activity and stability.[89] LMOs have also recently been deployed as a kind of versatile support to anchor metal species and tune the electronic structure. Zheng et al. successfully investigated a platinum (Pt)/LiCoO2 heterostructure consisting of homogeneous Pt nanoparticles confined by LiCoO2 nanosheets that was fabricated by a facile wet chemical strategy (Figure 14a).[78] Microscopic characterizations demonstrated that the Pt nanoparticles (NPs, ≈2.2 nm) were uniformly anchored on the LiCoO2 supports (Figure 14b–h). The obtained Pt/LiCoO2 heterostructures achieved an ultra‐low overpotential of 285 mV at a current density of 10 mA cm−2 (Figure 14i). The unique heterostructured Pt/LiCoO2 could act as an active‐center‐transferable electrocatalyst to accelerate both the hydrogen evolution reaction (HER) and the OER for hydrogen production (Figure 14j). In addition, the catalytic activity of the materials for the OER was significantly improved by Liu et al, through the continuous extraction of lithium ions from lithium transition metal phosphates.[62] In particular, Li(Ni, Fe)PO4 grown on rGO nanosheets exhibited remarkable activity and stability.14Figurea) Schematic diagram of the fabrication process for Pt/LiCoO2 heterostructures. b) SEM image of LiCoO2. c) Transmission electron microscope (TEM) image of exfoliated LiCoO2 nanosheets. d) TEM image of Pt/ Pt/LiCoO2. e) Selected area electron diffraction (SAED) pattern. f) Annular bright‐field (ABF)‐STEM and g) HAADF‐STEM image. h) Energy dispersive spectroscopy (EDS) elemental mapping of Co, O, and Pt. i) LSV curves of Pt/LiCoO2 samples and reference catalysts. j) Proposed catalytic mechanism for Pt/LiCoO2. Reproduced with permission.[78] Copyright 2020, Wiley‐VCH.Summary of OER Performance of LMOIn this section, we systematically compare the OER performance of typical metal oxides with M‐O,[90] M1‐O‐M2,[91] and Li‐O‐M structures.[13a,20,52,66,92] Figure 15a shows that dual metal oxides, including LMOs, can exhibit significantly improved performance compared to single metal oxides. Among them, the LMOs exhibit the lowest overpotential and Tafel slope, and the single metal oxides have high overpotential and a high Tafel slope. Synergistic effects between different metal sites can effectively overcome the kinetic deficiencies of the OER, such as modulating the electronic structure and increasing active centers.[93] As can be seen from the previous discussion, a significant proportion of research has been devoted to the doping of lithium ions into metal oxides to form bimetallic or polymetallic oxides. A long‐term durability of OER catalysts is another important features for proton exchange membrane (PEM) electrolyzer toward industrial applications.[6a] Catalysts, including LMOs, may undergo surface reconstruction during the OER process, which is effective in enhancing catalytic performance, but leads to catalyst instability. In addition, catalysts with more defects potentially have higher OER activity, but their stability is not fully satisfied. For these catalysts following the LOM pathway, it is more important to adjust the ligand structure to stabilize the lattice oxygen, and also to prepare more stable precursor supports to improve the durability. As shown in Figure 15b, chloride‐doped LiCoO1.8Cl indicates a highly stable OER performance over 500 h with a low potential at 1.5 V to achieve 10 mA cm−2. These results indicate the vital significance of LMO‐based OER catalysts in the future.[13a,20,23,47,52,61,62,66,75–77,85,87b,88,92,93b] Table 1 shows the OER performance of LMOs in recent years. Furthermore, Figure 15c,d ranks the overpotential and Tafel slope of various typical LMOs at 10 mA cm−2 current density.15Figurea) Overpotential and Tafel performance distributions of single metal oxides,[90] dual metal oxides,[91] and lithium metal oxides at 10 mA cm−2. b)  Stability of lithium metal oxides. c,d) Tafel slopes and overpotentials of lithium metal oxides at 10 mA cm−2.1TableSummary of OER performance of reported LMOsCatalystOverpotentialTafel slope [mV dec−1[ElectrolyteElectrodea)RefLiCo0.8Fe0.2O2340 mV (10 mA cm−2)500.1 m KOHGCE[52]LiCoO2430 mV (10 mA cm−2)830.1 m KOHGCE[52]LiNi0.8Al0.2O2340 mV (10 mA cm−2)440.1 m KOHGCE[87b]De‐LiCoO2380 mV(5 mA cm−2)500.1 m KOHCFP[20]De‐LiCo0.33Ni0.33Fe0.33O2300 mV(5 mA cm−2)350.1 m KOHCFP[20]De‐LiCo0.5Ni0.5O2370 mV(5 mA cm−2)420.1 m KOHCFP[20]De‐LiCo0.5Fe0.5O2340 mV(5 mA cm−2)400.1 m KOHCFP[20]LT‐LiCoO2520.1 m KOHGCE[47]LT‐Li0.5CoO2600.1 m KOHGCE[47]α‐Li2IrO3290 mV (10 mA cm−2)500.1 m KOHGCE[77]LiIrOx270 mV (10 mA cm−2)390.5 m H2SO4GCE[85]DO‐LiNi0.5Co0.2Mn0.3O2430 mV (10 mA cm−2)85.60.1 m KOHGCE[61]LT‐LiNi0.5Co0.2Mn0.3O2440 mV (1 mA cm−2)142.60.1 m KOHGCE[61]HT‐LiNi0.5Co0.2Mn0.3O2540 mV (1 mA cm−2)241.80.1 m KOHGCE[61]Exfoliated‐LiCo0.95Mg0.05O2329 mV (10 mA cm−2)33.81 m KOHGCE[66]LiCo0.95Mg0.05O263.71 m KOHGCE[66]Exfoliated‐LiCoO247.71 m KOHGCE[66]LiCoO2‐NS410 mV (10 mA cm−2)880.1 m KOHGCE[23]De‐LCO NPs390 mV (10 mA cm−2)570.1 m KOHCFP[75]30% Pt/LiCoO2285 mV (10 mA cm−2)46.81 m KOHGCE[92]LT‐LiCoO2430 mV (10 mA cm−2)481 m NaOHGCE[88]HT‐LiCoO2430 mV (10 mA cm−2)491 m NaOHGCE[88]LiCoO1.8Cl0.2270 mV (10 mA cm−2)55.41 m KOHGCE[13a]LiNi0.75Fe0.25PO4/rGO270 mV (10 mA cm−2)470.1 m KOHGCE[62]LiCo0.95Mg0.05O2329 mV (10 mA cm−2)1 m KOHGCE[66]1%La/LiCoO2330 mV (10 mA cm−2)1 m KOHGCE[94]a)GCE = glassy carbon electrode, CFP = carbon fiber papers.Chemistry behind LMO during the OERLMO‐based catalysts usually undergo chemical and structural evolution during the OER process, which is closely related to their activity and durability. Therefore, understanding the underlying surface chemistry is of critical significance to unravel the structure–performance relationships and establish a universal design strategy toward highly efficient electrocatalysts. In this section, we will unravel the surface chemistry of LMO during the OER from the aspects of lithium extraction, surface reconstruction, lattice oxygen activation, and oxidation state evolution (Figure 16).16FigureSchematic illustration of the chemistry behind changes to the LMO during the OER. Reproduced with permission.[66] Copyright 2019, Wiley‐VCH. Reproduced with permission.[61] Copyright 2020, American Chemical Society.Lithium Extraction and Surface ReconstructionSurface active sites determine the activity and selectivity of electrocatalyst–intermediate adsorption and stability. During the OER process, the electrocatalyst surface sites are completely dynamic in nature, which triggers reconstruction of the surface. Reconstruction connects the surface of the electrocatalyst with the real active sites involved in the OER process.[2b,70] The reconstruction process could trigger the evolution of the local electronic structure, coordination environment, M‐O covalency, and hydrophilicity of the catalyst.[13b,70b,95] Furthermore, the reconstruction process may change the surface of electrocatalyst reversibly or irreversibly, according to the structural characteristics of the electrocatalyst.[2b,96]For various metal oxides, the de‐embedding of lithium ions during the OER is a unique property of LMO materials. During the charging process, some of the lithium ions are extracted, and the negatively charged CoO generates stronger electrostatic repulsion, increasing the layer spacing. During the discharge process, lithium ions are intercalated and the lattice spacing is restored.[97] The stresses on the material can be quantitatively tuned by controlling the amount of de‐lithiation. Both compression and stretching can change the surface electronic structure, and thus the catalytic activity, by changing the distance between surface atoms.[97] Surface reconstruction accompanied by de‐lithiation can expose the true active center.[69] It was shown that both LT‐LiCoO2 and HT‐LiCoO2 undergo surface reformation in the first cycle of the OER, producing Co3O4, which may be the active species of the reaction.[22a] In addition, partial delamination of Li+ from layered LiCoO2 can complete the process of remodeling to cubic spinel LiCoO2.[73] Spinel‐type LiCo2O4 has a [Co4O4]n+ cubic subunit structure that provides a lower Co4+ oxidation potential. Many untreated LMOs do not have good performance, but cation or anion doping into LMOs can effectively change their electronic structure and trigger surface reconstruction, which, in turn, can enhance the OER performance of LMOs.[76,98] For example, doping with Cl− can reduce the potential for cobalt oxidation and lithium extraction.[76] The surface reconstruction of LiCoO2 without Cl− to spinel‐type Li1±xCo2O4 usually requires a higher electrochemical potential. In addition to this, the migration of Ir ions from the body to the surface in La2LiIrO6 catalyst leads to a drastic surface remodeling and the formation of IrO2 nanoparticles.[98]Activation of Lattice OxygenIt was found that the catalyst surface is no longer stable and changes dynamically with the OER process when following the LOM mechanism.[30c] The oxidation, exchange, and release of lattice oxygen ligands on the catalyst surface is critical to the OER performance.[98,99] The activation of lattice oxygen generally takes place at two adjacent metal sites, requiring the catalyst itself or the lattice oxygen itself to exhibit a unique electronic structure.[30c] Some LMO catalysts are able to allow direct coupling of *O intermediates and active lattice oxygen, and the newly formed *OO species become the O2 molecules produced in the subsequent OER cycle. In addition to this, the coupling of adjacent active lattice oxygen atoms can form M‐OO‐M, where *OO* molecules usually act as peroxides.[3c] The redox reactions of lattice oxygen can significantly enhance the OER activity, and some LMO catalysts can induce the activation of lattice oxygen by ligand cavities, and the electrophilic cavity‐active oxygen ligands can promote the formation of OO bonds.[98] For example, La2LiIrO6 undergoes dynamic reconstruction under oxidizing conditions, and the resulting electrostatic destabilization leads to a more significant effect on the O 2p band than the Ir 5d band, where surface oxygen ligand activation generates more ligand holes and iridium ion migration can activate lattice oxygen through ligand holes.[98] In addition, some researchers have found that lattice oxygen activation is more energetically favorable for high‐valence metal active sites by DFT calculations.[14] For example, LiNiO2 generates Li1−xNiO2/g‐NiOOH during the electrocatalytic process, and the high‐valence Ni ions in graphitic g‐NiOOH promote the formation of NiOO*. NiOOH completes deprotonation by forming ligand holes on the lattice oxygen to compensate the charge, which in turn promotes the OER activity.[59a]Change of Oxidation States in the MetalsAn increasing number of studies in the past have demonstrated that the oxidation state of the catalyst is related to the intrinsic activity of the OER.[14] Metal cations with higher oxidation states have higher metal‐oxygen covalency and thus lower charge transfer energy due to the contraction of the orbitals and shift of the valence band.[100] Among LMO catalysts, either the doping with other metal elements or the de‐embedding of lithium element is likely to regulate the oxidation state of the active metal cation. The higher the oxidation state of the cation, the easier it is to separate the electrons from the adsorbed oxygen ions.[101] The spinel‐structured LMOs have inherent mixed‐valence characteristics, with many gap sites favorable for cation migration.[102] Spinel‐type Li2Co2O4 will change from Co3+ to Co4+ oxidation state of the Co ions, with a change of voltage and the detachment of the Li ions during the OER process,[14] although the low spin state of Co ions and the edge‐sharing CoO network remain unchanged. Therefore, it can be inferred that the highly oxidized Co4+ site is the primary reason for the high catalytic activity of Li2Co2O4, rather than the Co3+ or oxygen vacancies.[14] In addition to lithium deoxidation, doping of LMOs can also effectively change their electronic structure.[87b] For example, doping Mg element into LiCoO2 can modulate the electronic structure of LiCoO2, where part of the Co3+ is oxidized to high‐valent Co4+, and also increases the CoO covalency. The OER performance of Mg‐doped LiCoO2 is significantly enhanced.[103] Al‐doped LiNiO2 transforms Ni3+/Ni2+ into Ni4+/Ni3+, and the Ni4+/Ni3+ octahedral sites in LiNi1−xAlxO2 are the real active centers of the OER, with the redox energy at the top of the O 2p band.[87b] In addition, some researchers found that the disordered structure of LiNi0.5Co0.2Mn0.3O2 has more significant OER properties than both its spinel counterpart and the layered LiNi0.5Co0.2Mn0.3O2. This is due to the presence of lithium vacancies in the disordered LiNi0.5Co0.2Mn0.3O2 crystal structure, which can change Ni ions from Ni2+ to Ni3+.[62]Conclusion and PerspectiveM‐O‐M type oxides typically exhibit significant catalytic properties compared to their unmodified counterparts, and the synergistic interaction between the metals will change the lattice parameters of the catalysts as well as the overlap between the atomic orbitals.[10] Notably, in a family of M‐O‐M oxides, lithium ions in LMOs can be inserted and extracted to produce irreversible changes in the catalyst surface, and the surface electronic structure will be significantly altered. In this paper, we review the recent research progress on LMO electrocatalysts. We not only outline the two OER mechanisms, AEM and LOM, but also summarize the modification principles of M‐O‐M type catalysts in terms of electronic states, vacancies, bonds, lattice oxygen activation, surface reconfiguration, and conductivity. In addition, we fully classify and summarize different types of LMOs and focus on their dynamic surface reconstruction, formation of lattice oxygen, and the valence evolution of active metal centers that LMOs undergo during the reaction process.Although extensive research progress has been made on various LMO catalysts used for the OER, most of the reported LMO catalysts have high overpotential, and their catalytic performance is still lower than the requirements of industrial applications. Although the activity of many reconstituted LMOs will increase, a decrease of stability may accompany this. In addition, the research and development of excellent electrocatalysts not only need flexible ideas and preparation methods, but also need advanced analysis technology. Therefore, in order to further improve the overall efficiency of the OER, we put forward two suggestions based on the existing problems:1)Designing new electrocatalysts. The reactions of many major metals lack the necessary combination of empty and full orbitals, so the catalytic OER is usually inert. Alkali and alkaline‐earth metals are traditionally used as thermal catalysts for organic reactions rather than as electrocatalysts. The active center of the catalysts is usually a 3d transition metal with variable valence, but doping with an alkali metal or alkaline earth metal can change the electronic structure of the electrocatalyst and increase the number of reaction sites, so that there is improvement of the slow dynamics of the OER.[51] The study of LMOs can effectively help us to understand the alkaline earth metal catalysts comprehensively and systematically, and provide a basis for a better understanding of their catalytic mechanism. Alkaline earth metals and alkali metals are candidates for highly active water electrolysis catalysts and the key to future research.2)Using in situ testing methods. OER is a complicated reacting system, which involves structural changes of catalysts, new phases formed on the interfaces, and absorbed small molecules. To gain a deep and empirical understanding of the OER chemistry, in situ techniques are urgently required (Figure 17). For example, LMOs undergo complex physicochemical changes during their electrochemical processes, and their true active centers are difficult to trace and identify. Thus, in situ X‐ray diffraction (XRD) and X‐ray absorption spectroscopy (XAS) testing techniques have been applied to the structural changes and oxidation of active sites of LMOs under OER conditions.[108] The oxidation of Ir to a higher oxidation state has been observed by in situ X‐ray absorption spectroscopy (XAS) in amorphous LiIrOx, but no such change was observed on IrO2.[108] Most of LMOs used for OER are composed of multiple metals. As the composition of catalysts becomes more complex, the difficulty is of defining the reaction paths. Therefore, in situ characterization techniques under OER conditions are necessary to monitor important intermediates, such as in situ Raman spectroscopy, ambient pressure X‐ray photoelectron spectroscopy (APXPS), and Mössbauer spectroscopy.[109] However, the currently existing in situ testing techniques have many limitations, and more characterization methods with high resolution are needed to monitor the dynamic structural evolution. Combining new in situ techniques with other characterizations can help researchers to understand more deeply with regard to the correlation between structure and activity of catalysts.17FigureSchematic illustration of in situ techniques, including: In situ Raman. Reproduced with permission.[101] Copyright 2017, American Chemical Society; In situ XAS. Reproduced with permission.[102] Copyright 2015, American Chemical Society; APXPS. Reproduced with permission.[103] Copyright 2015, American Chemical Society; and MÖssbauer spectroscopy. Reproduced with permission.[104] Copyright 2015, American Chemical Society.AcknowledgementsThis work is financially supported by the Beijing Municipal Natural Science Foundation (2212025). The authors thank Tania Silver for her critical reading and editing of this work.Open access publishing facilitated by University of Technology Sydney, as part of the Wiley ‐ University of Technology Sydney agreement via the Council of Australian University Librarians.Conflict of InterestThe authors declare no conflict of interest.a) M. Gong, H. Dai, Nano Res. 2015, 8, 23.b) S. Chu, Y. Cui, N. Liu, Nat. Mater. 2017, 16, 16;c) M. Z. Jacobson, W. G. Colella, D. M. Golden, Science 2005, 308, 1901;d) X. Yang, Y. Wang, C. M. Li, D. Wang, Nano Res. 2021, 14, 3446;e) Y. Yang, Y. Yang, Y. Liu, S. Zhao, Z. Tang, Small Sci. 2021, 1, 2100015;f) S. Zhao, C. Tan, C.‐T. He, P. An, F. Xie, S. Jiang, Y. Zhu, K.‐H. Wu, B. Zhang, H. Li, J. Zhang, Y. Chen, S. Liu, J. Dong, Z. Tang, Nat. Energy 2020, 5, 881;g) S. Zhao, Y. Yang, Z. Tang, Angew. Chem. 2022, 134, e202110186.a) L. Tian, X. Zhai, X. Wang, X. Pang, J. Li, Z. Li, Electrochim. Acta 2020, 337, 135823;b) N. C. S. Selvam, L. Du, B. Y. Xia, P. J. Yoo, B. You, Adv. Funct. Mater. 2021, 31, 2008190;c) S. Xu, H. Zhao, T. Li, J. Liang, S. Lu, G. Chen, S. Gao, A. M. Asiri, Q. Wu, X. Sun, J. Mater. Chem. A 2020, 8, 19729;d) X. Zheng, P. Li, S. Dou, W. Sun, H. Pan, D. Wang, Y. Li, Energy Environ. Sci. 2021, 14, 2809;e) X. Zheng, B. Li, Q. Wang, D. Wang, Y. Li, Nano Res. 2022, https://doi.org/10.1007/s12274-022-4429-9.a) S. Fukuzumi, Y. M. Lee, W. Nam, ChemSusChem 2017, 10, 4264;b) V. Kumaravel, A. Abdel‐Wahab, Energy Fuels 2018, 32, 6423;c) J. Zhang, W. Hu, S. Cao, L. Piao, Nano Res. 2020, 13, 2313.a) S. Satyapal, J. Petrovic, C. Read, G. Thomas, G. Ordaz, Catal. Today 2007, 120, 246;b) J. Yang, A. Sudik, C. Wolverton, D. J. Siegel, Chem. Soc. Rev. 2010, 39, 656;c) S. Jiang, H. Suo, T. Zhang, C. Liao, Y. Wang, Q. Zhao, W. Lai, Catalysts 2022, 12, 123.D. T. Tran, T. Kshetri, D. C. Nguyen, J. Gautam, V. H. Hoa, H. T. Le, N. H. Kim, J. H. Lee, Nano Today 2018, 22, 100.a) F.‐Y. Chen, Z.‐Y. Wu, Z. Adler, H. Wang, Joule 2021, 5, 1704;b) L. A. King, M. A. Hubert, C. Capuano, J. Manco, N. Danilovic, E. Valle, T. R. Hellstern, K. Ayers, T. F. Jaramillo, Nat. Nanotechnol. 2019, 14, 1071;c) P. Lettenmeier, R. Wang, R. Abouatallah, S. Helmly, T. Morawietz, R. Hiesgen, S. Kolb, F. Burggraf, J. Kallo, A. S. Gago, Electrochim. Acta 2016, 210, 502.a) M. W. Kanan, D. G. Nocera, Science 2008, 321, 1072;b) J. Park, H. Kim, K. Jin, B. J. Lee, Y.‐S. Park, H. Kim, I. Park, K. D. Yang, H.‐Y. Jeong, J. Kim, J. Am. Chem. Soc. 2014, 136, 4201;c) J. S. Kim, I. Park, E. S. Jeong, K. Jin, W. M. Seong, G. Yoon, H. Kim, B. Kim, K. T. Nam, K. Kang, Adv. Mater. 2017, 29, 1606893;d) H. Kim, J. Park, I. Park, K. Jin, S. E. Jerng, S. H. Kim, K. T. Nam, K. Kang, Nat. Commun. 2015, 6, 8253.J. S. Kim, B. Kim, H. Kim, K. Kang, Adv. Energy Mater. 2018, 8, 1702774.a) D. A. Corrigan, J. Electrochem. Soc. 1987, 134, 377;b) R. Singh, J. Pandey, N. Singh, B. Lal, P. Chartier, J.‐F. Koenig, Electrochim. Acta 2000, 45, 1911.a) Y. C. Lin, Z. Q. Tian, L. J. Zhang, J. Y. Ma, Z. Jiang, B. J. Deibert, R. X. Ge, L. Chen, Nat. Commun. 2019, 10, 162;b) Y. H. Wang, S. Y. Hao, X. N. Liu, Q. Q. Wang, Z. W. Su, L. C. Lei, X. W. Zhang, ACS Appl. Mater. Interfaces 2020, 12, 37006;c) F. Lv, J. R. Feng, K. Wang, Z. P. Dou, W. Y. Zhang, J. H. Zhou, C. Yang, M. C. Luo, Y. Yang, Y. J. Li, P. Gao, S. J. Guo, ACS Cent. Sci. 2018, 4, 1244;d) Z. Li, S. Wang, Y. Y. Tian, B. H. Li, H. J. Yan, S. Zhang, Z. M. Liu, Q. J. Zhang, Y. C. Lin, L. Chen, Chem. Commun. 2020, 56, 1749;e) R. X. Ge, L. Li, J. W. Su, Y. C. Lin, Z. Q. Tian, L. Chen, Adv. Energy Mater. 2019, 9, 1901313.f) S. R. Ede, Z. P. Luo, J. Mater. Chem. A 2021, 9, 20131.a) B. Cui, H. Lin, J. B. Li, X. Li, J. Yang, J. Tao, Adv. Funct. Mater. 2008, 18, 1440;b) S. Chen, S.‐Z. Qiao, ACS Nano 2013, 7, 10190.I. Nikolov, R. Darkaoui, E. Zhecheva, R. Stoyanova, N. Dimitrov, T. Vitanov, J. Electroanal. Chem. 1997, 429, 157.a) J. Wang, S.‐J. Kim, J. Liu, Y. Gao, S. Choi, J. Han, H. Shin, S. Jo, J. Kim, F. Ciucci, Nat. Catal. 2021, 4, 212;b) Y. Li, X. Du, J. Huang, C. Wu, Y. Sun, G. Zou, C. Yang, J. Xiong, Small 2019, 15, 1901980.J. Zhou, L. Zhang, Y.‐C. Huang, C.‐L. Dong, H.‐J. Lin, C.‐T. Chen, L. Tjeng, Z. Hu, Nat. Commun. 2020, 11, 1984.a) D. Xu, M. B. Stevens, Y. Rui, G. DeLuca, S. W. Boettcher, E. Reichmanis, Y. Li, Q. Zhang, H. Wang, Electrochim. Acta 2018, 265, 10;b) N. Zhang, X. Feng, D. Rao, X. Deng, L. Cai, B. Qiu, R. Long, Y. Xiong, Y. Lu, Y. Chai, Nat. Commun. 2020, 11, 4066;c) B. Zhang, K. Jiang, H. Wang, S. Hu, Nano Lett. 2018, 19, 530.H. Jiang, Q. He, Y. Zhang, L. Song, Acc. Chem. Res. 2018, 51, 2968.M. Wang, Y. Wang, S. S. Mao, S. Shen, Nano Energy 2021, 88, 106216.J. Chen, F. Zheng, S.‐J. Zhang, A. Fisher, Y. Zhou, Z. Wang, Y. Li, B.‐B. Xu, J.‐T. Li, S.‐G. Sun, ACS Catal. 2018, 8, 11342.K. Liu, C. Zhang, Y. Sun, G. Zhang, X. Shen, F. Zou, H. Zhang, Z. Wu, E. C. Wegener, C. J. Taubert, J. T. Miller, Z. Peng, Y. Zhu, ACS Nano 2018, 12, 158.Z. Lu, H. Wang, D. Kong, K. Yan, P.‐C. Hsu, G. Zheng, H. Yao, Z. Liang, X. Sun, Y. Cui, Nat. Commun. 2020, 11, 4354.a) N. Nitta, F. Wu, J. T. Lee, G. Yushin, Mater. Today 2015, 18, 252;b) J.‐Z. Kong, F. Zhou, C.‐B. Wang, X.‐Y. Yang, H.‐F. Zhai, H. Li, J.‐X. Li, Z. Tang, S.‐Q. Zhang, J. Alloys Compd. 2013, 554, 221;c) Y.‐S. Lee, D. Ahn, Y.‐H. Cho, T. E. Hong, J. Cho, J. Electrochem. Soc. 2011, 158, A1354;d) J.‐Z. Kong, H.‐F. Zhai, C. Ren, G.‐A. Tai, X.‐Y. Yang, F. Zhou, H. Li, J.‐X. Li, Z. Tang, J. Solid State Electrochem. 2013, 18, 181;e) S. W. Lee, C. Carlton, M. Risch, Y. Surendranath, S. Chen, S. Furutsuki, A. Yamada, D. G. Nocera, Y. Shao‐Horn, J. Am. Chem. Soc. 2012, 134, 16959.a) N. Colligan, V. Augustyn, A. Manthiram, J. Phys. Chem. C 2015, 119, 2335;b) X. Zheng, J. Yang, Z. Xu, Q. Wang, J. Wu, E. Zhang, S. Dou, W. Sun, D. Wang, Y. Li, Angew. Chem., Int. Ed. 2022, n/a, e202205946.J. Wang, L. Li, H. Tian, Y. Zhang, X. Che, G. Li, ACS Appl. Mater. Interfaces 2017, 9, 7100.a) X. Zhang, L. An, J. Yin, P. Xi, Z. Zheng, Y. Du, Sci. Rep. 2017, 7, 43590;b) F. Yang, K. Sliozberg, I. Sinev, H. Antoni, A. Bähr, K. Ollegott, W. Xia, J. Masa, W. Grünert, B. R. Cuenya, W. Schuhmann, M. Muhler, ChemSusChem 2017, 10, 156;c) C. Dong, X. Yuan, X. Wang, X. Liu, W. Dong, R. Wang, Y. Duan, F. Huang, J. Mater. Chem. A 2016, 4, 11292;d) C. Tang, H.‐S. Wang, H.‐F. Wang, Q. Zhang, G.‐L. Tian, J.‐Q. Nie, F. Wei, Adv. Mater. 2015, 27, 4516;e) H. Huang, C. Yu, C. Zhao, X. Han, J. Yang, Z. Liu, S. Li, M. Zhang, J. Qiu, Nano Energy 2017, 34, 472;f) W. Ma, R. Ma, C. Wang, J. Liang, X. Liu, K. Zhou, T. Sasaki, ACS Nano 2015, 9, 1977.a) J.‐S. Li, L.‐X. Kong, Z. Wu, S. Zhang, X.‐Y. Yang, J.‐Q. Sha, G.‐D. Liu, Carbon 2019, 145, 694;b) Y. Pan, K. Sun, S. Liu, X. Cao, K. Wu, W.‐C. Cheong, Z. Chen, Y. Wang, Y. Li, Y. Liu, D. Wang, Q. Peng, C. Chen, Y. Li, J. Am. Chem. Soc. 2018, 140, 2610;c) C.‐C. Hou, S. Cao, W.‐F. Fu, Y. Chen, ACS Appl. Mater. Interfaces 2015, 7, 28412;d) J. Wang, W. Yang, J. Liu, J. Mater. Chem. A 2016, 4, 4686;e) L. Yu, Y. Xiao, C. Luan, J. Yang, H. Qiao, Y. Wang, X. Zhang, X. Dai, Y. Yang, H. Zhao, ACS Appl. Mater. Interfaces 2019, 11, 6890;f) Y. Wang, T. Williams, T. Gengenbach, B. Kong, D. Zhao, H. Wang, C. Selomulya, Nanoscale 2017, 9, 17349;g) L. Yan, L. Cao, P. Dai, X. Gu, D. Liu, L. Li, Y. Wang, X. Zhao, Adv. Funct. Mater. 2017, 27, 1703455.a) F. Cao, X. Yang, C. Shen, X. Li, J. Wang, G. Qin, S. Li, X. Pang, G. Li, J. Mater. Chem. A 2020, 8, 7245;b) P. Jiang, Y. Yang, R. Shi, G. Xia, J. Chen, J. Su, Q. Chen, J. Mater. Chem. A 2017, 5, 5475;c) Q. Kang, D. Lai, W. Tang, Q. Lu, F. Gao, Chem. Sci. 2021, 12, 3818.d) K. Huang, B. Zhang, J. Wu, T. Zhang, D. Peng, X. Cao, Z. Zhang, Z. Li, Y. Huang, J. Mater. Chem. A 2020, 8, 11938.S. Gottesfeld, S. Srinivasan, J. Electroanal. Chem. Interfacial Electrochem. 1978, 86, 89.a) V. I. Birss, A. Damjanovic, P. Hudson, J. Electrochem. Soc. 1986, 133, 1621.b) B. E. Conway, T. Liu, Langmuir 1990, 6, 268.I. Hamidah, S. Sriyono, M. N. Hudha, Indones. J. Sci. Technol. 2020, 5, 34.a) B. M. Hunter, H. B. Gray, A. M. Muller, Chem. Rev. 2016, 116, 14120;b) C. Hu, L. Zhang, J. Gong, Nat. Rev. Chem. 2017, 1, 0003;c) J. Song, C. Wei, Z.‐F. Huang, C. Liu, L. Zeng, X. Wang, Z. J. Xu, Chem. Soc. Rev. 2020, 49, 2196;d) F. Song, L. Bai, A. Moysiadou, S. Lee, C. Hu, L. Liardet, X. Hu, J. Am. Chem. Soc. 2018, 140, 7748;e) N.‐T. Suen, S.‐F. Hung, Q. Quan, N. Zhang, Y.‐J. Xu, H. M. Chen, Chem. Soc. Rev. 2017, 46, 337.N. Zhang, Y. Chai, Energy Environ. Sci. 2021, 14, 4647.Y. Sun, H. Liao, J. Wang, B. Chen, S. Sun, S. J. H. Ong, S. Xi, C. Diao, Y. Du, J.‐O. Wang, M. B. H. Breese, S. Li, H. Zhang, Z. J. Xu, Nat. Catal. 2020, 3, 554.a) J. H. Montoya, L. C. Seitz, P. Chakthranont, A. Vojvodic, T. F. Jaramillo, J. K. Nørskov, Nat. Mater. 2017, 16, 70;b) I. C. Man, H. Y. Su, F. Calle‐Vallejo, H. A. Hansen, J. I. Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. K. Nørskov, J. Rossmeisl, ChemCatChem 2011, 3, 1159;c) L. C. Seitz, C. F. Dickens, K. Nishio, Y. Hikita, J. Montoya, A. Doyle, C. Kirk, A. Vojvodic, H. Y. Hwang, J. K. Norskov, T. F. Jaramillo, Science 2016, 353, 1011;d) J. K. Nørskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J. R. Kitchin, T. Bligaard, H. Jonsson, J. Phys. Chem. B 2004, 108, 17886;e) J. Rossmeisl, A. Logadottir, J. K. Nørskov, Chem. Phys. 2005, 319, 178.a) D. A. Kuznetsov, M. A. Naeem, P. V. Kumar, P. M. Abdala, A. Fedorov, C. R. Müller, J. Am. Chem. Soc. 2020, 142, 7883;b) X. Rong, J. Parolin, A. M. Kolpak, ACS Catal. 2016, 6, 1153.a) J. T. Mefford, X. Rong, A. M. Abakumov, W. G. Hardin, S. Dai, A. M. Kolpak, K. P. Johnston, K. J. Stevenson, Nat. Commun. 2016, 7, 11053;b) A. Grimaud, W. T. Hong, Y. Shao‐Horn, J.‐M. Tarascon, Nat. Mater. 2016, 15, 121;c) A. Grimaud, O. Diaz‐Morales, B. Han, W. T. Hong, Y.‐L. Lee, L. Giordano, K. A. Stoerzinger, M. T. Koper, Y. Shao‐Horn, Nat. Chem. 2017, 9, 457;d) Y. Yan, J. Lin, J. Cao, S. Guo, X. Zheng, J. Feng, J. Qi, J. Mater. Chem. A 2019, 7, 24486;e) X. Cheng, E. Fabbri, Y. Yamashita, I. E. Castelli, B. Kim, M. Uchida, R. Haumont, I. Puente‐Orench, T. J. Schmidt, ACS Catal. 2018, 8, 9567.a) C. Z. Yuan, H. B. Wu, Y. Xie, X. W. Lou, Angew. Chem., Int. Ed. 2014, 53, 1488;b) M. Hamdani, R. N. Singh, P. Chartier, Int. J. Electrochem. Sci. 2010, 5, 556;c) L. F. Hu, L. M. Wu, M. Y. Liao, X. H. Hu, X. S. Fang, Adv. Funct. Mater. 2012, 22, 998;d) I. Katsounaros, S. Cherevko, A. R. Zeradjanin, K. J. J. Mayrhofer, Angew. Chem., Int. Ed. 2014, 53, 102;e) R. Kotz, S. Stucki, Electrochim. Acta 1986, 31, 1311;f) X. B. Zheng, Y. P. Chen, X. S. Zheng, C. Q. Zhao, K. Rui, P. Li, X. Xu, Z. X. Cheng, S. X. Dou, W. P. Sun, Adv. Energy Mater. 2019, 9, 1803482.a) F. Calle‐Vallejo, M. T. Koper, A. S. Bandarenka, Chem. Soc. Rev. 2013, 42, 5210;b) I. E. Stephens, A. S. Bondarenko, F. J. Perez‐Alonso, F. Calle‐Vallejo, L. Bech, T. P. Johansson, A. K. Jepsen, R. Frydendal, B. P. Knudsen, J. Rossmeisl, J. Am. Chem. Soc. 2011, 133, 5485;c) T. Bligaard, J. K. Nørskov, Electrochim. Acta 2007, 52, 5512;d) Z. Xu, J. R. Kitchin, J. Chem. Phys. 2015, 142, 104703;e) J. R. Kitchin, J. K. Nørskov, M. A. Barteau, J. Chen, Phys. Rev. Lett. 2004, 93, 156801.M. Grisolia, J. Varignon, G. Sanchez‐Santolino, A. Arora, S. Valencia, M. Varela, R. Abrudan, E. Weschke, E. Schierle, J. Rault, Nat. Phys. 2016, 12, 484.a) C. J. Ballhausen, H. B. Gray, Inorg. Chem. 1962, 1, 111.b) T. A. Betley, Q. Wu, T. Van Voorhis, D. G. Nocera, lnorg. Chem. 2008, 47, 1849.a) X. Li, Z. Cheng, X. Wang, Electrochem. Energy Rev. 2021, 4, 136;b) J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. J. S. Shao‐Horn, Science 2011, 334, 1383.C. Wei, Z. Feng, G. G. Scherer, J. Barber, Y. Shao‐Horn, Z. J. Xu, Adv. Mater. 2017, 29, 1606800.A. Houmam, Chem. Rev. 2008, 108, 2180.J. Li, D. Chu, H. Dong, D. R. Baker, R. Jiang, J. Am. Chem. Soc. 2020, 142, 50.E. Hu, X. Yu, R. Lin, X. Bi, J. Lu, S. Bak, K.‐W. Nam, H. L. Xin, C. Jaye, D. A. Fischer, K. Amine, X.‐Q. Yang, Nat. Energy 2018, 3, 690.S. Zhou, X. Miao, X. Zhao, C. Ma, Y. Qiu, Z. Hu, J. Zhao, L. Shi, J. Zeng, Nat. Commun. 2016, 7, 11510.Y. Duan, S. Sun, S. Xi, X. Ren, Y. Zhou, G. Zhang, H. Yang, Y. Du, Z. J. Xu, Chem. Mater. 2017, 29, 10534.T. Maiyalagan, K. A. Jarvis, S. Therese, P. J. Ferreira, A. Manthiram, Nat. Commun. 2014, 5, 3949.a) B. Han, D. Qian, M. Risch, H. Chen, M. Chi, Y. S. Meng, Y. Shao‐Horn, J. Phys. Chem. Lett. 2015, 6, 1357;b) F. Calle‐Vallejo, N. G. Inoglu, H.‐Y. Su, J. I. Martinez, I. C. Man, M. T. Koper, J. R. Kitchin, J. Rossmeisl, Chem. Sci. 2013, 4, 1245.Y. Li, P. Hasin, Y. Wu, Adv. Mater. 2010, 22, 1926.J. Haenen, W. Visscher, E. Barendrecht, J. Electroanal. Chem. Interfacial Electrochem. 1986, 208, 273.H. Wang, J. Wu, A. Dolocan, Y. Li, X. Lü, N. Wu, K. Park, S. Xin, M. Lei, W. Yang, J. B. Goodenough, Proc. Natl. Acad. Sci. U. S. A. 2019, 116, 23473.Y. Zhu, W. Zhou, Y. Chen, J. Yu, M. Liu, Z. Shao, Adv. Mater. 2015, 27, 7150.J. Qin, V. P. Pasko, M. G. McHarg, H. C. Stenbaek‐Nielsen, Nat. Commun. 2014, 5, 3740.a) J. Li, C. Shu, C. Liu, X. Chen, A. Hu, J. Long, Small 2020, 16, 2001812;b) J. Peng, Y. Yuan, W. Yuan, K. Peng, Int. J. Hydrogen Energy 2021, 46, 24117;c) J. Qi, T. Xu, J. Cao, S. Guo, Z. Zhong, J. Feng, Nanoscale 2020, 12, 6204;d) Z.‐h. Xiao, D.‐c. Jiang, H. Xu, J.‐t. Zhou, Q.‐z. Zhang, P.‐w. Du, Z.‐l. Luo, C. Gao, Chin. J. Chem. Phys. 2018, 31, 691;e) H. Yang, H. Sun, X. Fan, X. Wang, Q. Yang, X. Lai, Mater. Chem. Front. 2021, 5, 259;f) X. Li, Y. Sun, F. Ren, Y. Bai, Z. Cheng, Mater. Today Energy. 2021, 19, 100619.g) K. Zhang, G. Zhang, J. Qu, H. Liu, Small 2018, 14, 1802760.a) D. Chen, M. Qiao, Y. R. Lu, L. Hao, D. Liu, C. L. Dong, Y. Li, S. Wang, Angew. Chem., Int. Ed. 2018, 57, 8691;b) L. Pan, S. Wang, W. Mi, J. Song, J.‐J. Zou, L. Wang, X. Zhang, Nano Energy 2014, 9, 71;c) S. Wang, L. Pan, J.‐J. Song, W. Mi, J.‐J. Zou, L. Wang, X. Zhang, J. Am. Chem. Soc. 2015, 137, 2975.H. N. Nong, T. Reier, H.‐S. Oh, M. Gliech, P. Paciok, T. H. T. Vu, D. Teschner, M. Heggen, V. Petkov, R. Schlögl, Nat. Catal. 2018, 1, 841.T. Ling, D.‐Y. Yan, Y. Jiao, H. Wang, Y. Zheng, X. Zheng, J. Mao, X.‐W. Du, Z. Hu, M. Jaroniec, Nat. Commun. 2016, 7, 12876.P. W. Menezes, A. Indra, A. Bergmann, P. Chernev, C. Walter, H. Dau, P. Strasser, M. Driess, J. Mater. Chem. A 2016, 4, 10014.a) X. Ren, C. Wei, Y. Sun, X. Liu, F. Meng, X. Meng, S. Sun, S. Xi, Y. Du, Z. Bi, G. Shang, A. C. Fisher, L. Gu, Z. J. Xu, Adv. Mater. 2020, 32, 2001292;b) S. Sun, Y. Sun, Y. Zhou, S. Xi, X. Ren, B. Huang, H. Liao, L. P. Wang, Y. Du, Z. J. Xu, Angew. Chem. 2019, 131, 6103.X. Zheng, Y. Chen, W. Lai, P. Li, C. Ye, N. Liu, S. X. Dou, H. Pan, W. Sun, Adv. Funct. Mater. 2022, 32, 2200663.D. Huang, J. Yu, Z. Zhang, C. Engtrakul, A. Burrell, M. Zhou, H. Luo, R. C. Tenent, ACS Appl. Mater. Interfaces 2020, 12, 10496.Y. Liu, H. Wang, D. Lin, C. Liu, P.‐C. Hsu, W. Liu, W. Chen, Y. Cui, Energy Environ. Sci. 2015, 8, 1719.J. Hwang, R. R. Rao, L. Giordano, Y. Katayama, Y. Yu, Y. Shao‐Horn, Science 2017, 358, 751.J. Suntivich, W. T. Hong, Y.‐L. Lee, J. M. Rondinelli, W. Yang, J. B. Goodenough, B. Dabrowski, J. W. Freeland, Y. Shao‐Horn, J. Phys. Chem. C 2014, 118, 1856.N. Zhang, C. Wang, J. Chen, C. Hu, J. Ma, X. Deng, B. Qiu, L. Cai, Y. Xiong, Y. Chai, ACS Nano 2021, 15, 8537.X. Zheng, Y. Chen, X. Zheng, G. Zhao, K. Rui, P. Li, X. Xu, Z. Cheng, S. X. Dou, W. Sun, Adv. Energy Mater. 2019, 9, 1803482.M. Sathiya, G. Rousse, K. Ramesha, C. P. Laisa, H. Vezin, M. T. Sougrati, M. L. Doublet, D. Foix, D. Gonbeau, W. Walker, A. S. Prakash, M. Ben Hassine, L. Dupont, J. M. Tarascon, Nat. Mater. 2013, 12, 827.W.‐K. Han, J.‐X. Wei, K. Xiao, T. Ouyang, X. Peng, S. Zhao, Z.‐Q. Liu, Angew. Chem., Int. Ed. 2022, e202206050.Z. Lu, H. Wang, D. Kong, K. Yan, P.‐C. Hsu, G. Zheng, H. Yao, Z. Liang, X. Sun, Y. Cui, Nat. Commun. 2014, 5, 4345.a) K. J. Lee, B. D. McCarthy, J. L. Dempsey, Chem. Soc. Rev. 2019, 48, 2927;b) A. Sivanantham, P. Ganesan, A. Vinu, S. Shanmugam, ACS Catal. 2019, 10, 463.a) Z. Lu, K. Jiang, G. Chen, H. Wang, Y. Cui, Adv. Mater. 2018, 30, 1800978;b) K. Mizushima, P. Jones, P. Wiseman, J. B. Goodenough, Mater. Res. Bull. 1980, 15, 783.G. P. Gardner, Y. B. Go, D. M. Robinson, P. F. Smith, J. Hadermann, A. Abakumov, M. Greenblatt, G. C. Dismukes, Angew. Chem., Int. Ed. 2012, 51, 1616.G. Gardner, J. Al‐Sharab, N. Danilovic, Y. B. Go, K. Ayers, M. Greenblatt, G. Charles Dismukes, Energy Environ. Sci. 2016, 9, 184.G. P. Gardner, Y. B. Go, D. M. Robinson, P. F. Smith, J. Hadermann, A. Abakumov, M. Greenblatt, G. C. Dismukes, Angew. Chem., Int. Ed. Engl. 2012, 51, 1616.Z. Lu, G. Chen, Y. Li, H. Wang, J. Xie, L. Liao, C. Liu, Y. Liu, T. Wu, Y. Li, A. C. Luntz, M. Bajdich, Y. Cui, J. Am. Chem. Soc. 2017, 139, 6270.J. Wang, S.‐J. Kim, J. Liu, Y. Gao, S. Choi, J. Han, H. Shin, S. Jo, J. Kim, F. Ciucci, H. Kim, Q. Li, W. Yang, X. Long, S. Yang, S.‐P. Cho, K. H. Chae, M. G. Kim, H. Kim, J. Lim, Nat. Catal. 2021, 4, 212.C. Yang, G. Rousse, K. L. Svane, P. E. Pearce, A. M. Abakumov, M. Deschamps, G. Cibin, A. V. Chadwick, D. A. D. Corte, H. A. Hansen, T. Vegge, J. M. Tarascon, A. Grimaud, Nat. Commun. 2020, 11, 1378.X. Zheng, P. Cui, Y. Qian, G. Zhao, X. Zheng, X. Xu, Z. Cheng, Y. Liu, S. X. Dou, W. Sun, Angew. Chem., Int. Ed. Engl. 2020, 59, 14533.J. Wang, L. Li, H. Tian, Y. Zhang, X. Che, G. Li, ACS Appl. Mater. Interfaces 2017, 9, 7100.a) R. Gummow, D. Liles, M. Thackeray, Mater. Res. Bull. 1993, 28, 235;b) R. Gummow, M. Thackeray, W. David, S. Hull, Mater. Res. Bull. 1992, 27, 327.Z. Chen, J. Wang, D. Chao, T. Baikie, L. Bai, S. Chen, Y. Zhao, T. C. Sum, J. Lin, Z. Shen, Sci. Rep. 2016, 6, 25771.a) X. Zhang, W. J. Jiang, A. Mauger, Qilu, F. Gendron, C. M. Julien, J. Power Sources 2010, 195, 1292;b) D. Wang, X. Li, Z. Wang, H. Guo, Y. Xu, Y. Fan, J. Ru, Electrochim. Acta 2016, 188, 48.D. Qian, Y. Hinuma, H. Chen, L. S. Du, K. J. Carroll, G. Ceder, C. P. Grey, Y. S. Meng, J. Am. Chem. Soc. 2012, 134, 6096.a) A. Grimaud, K. J. May, C. E. Carlton, Y. L. Lee, M. Risch, W. T. Hong, J. Zhou, Y. Shao‐Horn, Nat. Commun. 2013, 4, 2439;b) J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. Shao‐Horn, Science 2011, 334, 1383;c) B. J. Kim, E. Fabbri, D. F. Abbott, X. Cheng, A. H. Clark, M. Nachtegaal, M. Borlaf, I. E. Castelli, T. Graule, T. J. Schmidt, J. Am. Chem. Soc. 2019, 141, 5231;d) F. Calle‐Vallejo, O. A. Díaz‐Morales, M. J. Kolb, M. T. M. Koper, ACS Catal. 2015, 5, 869.J. Gao, C.‐Q. Xu, S.‐F. Hung, W. Liu, W. Cai, Z. Zeng, C. Jia, H. M. Chen, H. Xiao, J. Li, J. Am. Chem. Soc. 2019, 141, 3014.a) F. Wang, Y. Han, C. S. Lim, Y. Lu, J. Wang, J. Xu, H. Chen, C. Zhang, M. Hong, X. Liu, Nature 2010, 463, 1061;b) X. Feng, D. C. Sayle, Z. L. Wang, M. S. Paras, B. Santora, A. C. Sutorik, T. X. Sayle, Y. Yang, Y. Ding, X. Wang, Y. S. Her, Science 2006, 312, 1504.a) M. Guilmard, J. Power Sources 2003, 115, 305;b) A. Gupta, W. D. Chemelewski, C. Buddie Mullins, J. B. Goodenough, Adv. Mater. 2015, 27, 6063.G. Gardner, J. Al‐Sharab, N. Danilovic, Y. B. Go, K. Ayers, M. Greenblatt, G. C. Dismukes, Energy Environ. Sci. 2016, 9, 184.a) B. S. Yeo, A. T. Bell, J. Phys. Chem. C 2012, 116, 8394;b) Y. Gorlin, C. J. Chung, J. D. Benck, D. Nordlund, L. Seitz, T. C. Weng, D. Sokaras, B. M. Clemens, T. F. Jaramillo, J. Am. Chem. Soc. 2014, 136, 4920;c) G. Zhao, P. Li, N. Cheng, S. X. Dou, W. Sun, Adv. Mater. 2020, 32, 2000872;d) R. Subbaraman, D. Tripkovic, D. Strmcnik, K. C. Chang, M. Uchimura, A. P. Paulikas, V. Stamenkovic, N. M. Markovic, Science 2011, 334, 1256;e) H. Tang, J. Wei, F. Liu, B. Qiao, X. Pan, L. Li, J. Liu, J. Wang, T. Zhang, J. Am. Chem. Soc. 2016, 138, 56.a) Y. Yang, X. Su, L. Zhang, P. Kerns, L. Achola, V. Hayes, R. Quardokus, S. L. Suib, J. J. C. He, ChemCatChem 2019, 11, 1689;b) J. S. Hong, H. Seo, Y. H. Lee, K. H. Cho, C. Ko, S. Park, K. T. Nam, Small Methods 2020, 4, 1900733;c) C. Meng, Y.‐F. Gao, X.‐M. Chen, Y.‐X. Li, M.‐C. Lin, Y. Zhou, ACS Sustainable Chem. Eng. 2019, 7, 18055;d) W. Gou, M. Zhang, Y. Zou, X. Zhou, Y. Qu, ChemCatChem 2019, 11, 6008.a) H. Shi, G. Zhao, J. Phys. Chem. C 2014, 118, 25939;b) T. W. Kim, M. A. Woo, M. Regis, K.‐S. Choi, J. Phys. Chem. Lett. 2014, 5, 2370;c) X. Liu, Z. Chang, L. Luo, T. Xu, X. Lei, J. Liu, X. Sun, Chem. Mater. 2014, 26, 1889;d) J. Zhang, D. Zhang, Y. Yang, J. Ma, S. Cui, Y. Li, B. Yuan, RSC Adv. 2016, 6, 92699;e) J. Landon, E. Demeter, N. İnoğlu, C. Keturakis, I. E. Wachs, R. Vasić, A. I. Frenkel, J. R. Kitchin, ACS Catal. 2012, 2, 1793;f) A. Indra, P. W. Menezes, N. R. Sahraie, A. Bergmann, C. Das, M. Tallarida, D. Schmeißer, P. Strasser, M. Driess, J. Am. Chem. Soc. 2014, 136, 17530;g) G. Karkera, T. Sarkar, M. D. Bharadwaj, A. S. Prakash, ChemCatChem 2017, 9, 3681.X. Zheng, P. Cui, Y. Qian, G. Zhao, X. Zheng, X. Xu, Z. Cheng, Y. Liu, S. X. Dou, W. Sun, Angew. Chem. 2020, 132, 14641.J. W. D. Ng, M. García‐Melchor, M. Bajdich, P. Chakthranont, C. Kirk, A. Vojvodic, T. F. Jaramillo, Nat. Energy 2016, 1, 16053.Z. R. Zhang, C. X. Liu, C. Feng, P. F. Gao, Y. L. Liu, F. N. Ren, Y. F. Zhu, C. Cao, W. S. Yan, R. Si, S. M. Zhou, J. Zeng, Nano Lett. 2019, 19, 8774.J. Shan, Y. Zheng, B. Shi, K. Davey, S.‐Z. Qiao, ACS Energy Lett. 2019, 4, 2719.a) N. Zhang, X. Feng, D. Rao, X. Deng, L. Cai, B. Qiu, R. Long, Y. Xiong, Y. Lu, Y. Chai, Nat. Commun. 2020, 11, 4066;b) E. Fabbri, D. F. Abbott, M. Nachtegaal, T. J. Schmidt, Curr. Opin. Electrochem. 2017, 5, 20;c) D. Guan, G. Ryu, Z. Hu, J. Zhou, C. L. Dong, Y. C. Huang, K. Zhang, Y. Zhong, A. C. Komarek, M. Zhu, X. Wu, C. W. Pao, C. K. Chang, H. J. Lin, C. T. Chen, W. Zhou, Z. Shao, Nat. Commun. 2020, 11, 3376;d) C. Walter, P. W. Menezes, S. Orthmann, J. Schuch, P. Connor, B. Kaiser, M. Lerch, M. Driess, Angew. Chem., Int. Ed. Engl. 2018, 57, 698;e) C. W. Song, H. Suh, J. Bak, H. B. Bae, S.‐Y. Chung, Chem 2019, 5, 3243;f) Y. Zhou, N. López, ACS Catal. 2020, 10, 6254;g) C. Lee, K. Shin, C. Jung, P.‐P. Choi, G. Henkelman, H. M. Lee, ACS Catal. 2019, 10, 562.H. Wang, S. Xu, C. Tsai, Y. Li, C. Liu, J. Zhao, Y. Liu, H. Yuan, F. Abild‐Pedersen, F. B. Prinz, Science 2016, 354, 1031.A. Grimaud, A. Demortière, M. Saubanère, W. Dachraoui, M. Duchamp, M.‐L. Doublet, J.‐M. Tarascon, Nat. Energy 2016, 2, 16189.T. M. Anderson, R. Cao, E. Slonkina, B. Hedman, K. O. Hodgson, K. I. Hardcastle, W. A. Neiwert, S. Wu, M. L. Kirk, S. Knottenbelt, E. C. Depperman, B. Keita, L. Nadjo, D. G. Musaev, K. Morokuma, C. L. Hill, J. Am. Chem. Soc. 2005, 127, 11948.M. N. Grisolia, J. Varignon, G. Sanchez‐Santolino, A. Arora, S. Valencia, M. Varela, R. Abrudan, E. Weschke, E. Schierle, J. E. Rault, J. P. Rueff, A. Barthélémy, J. Santamaria, M. Bibes, Nat. Phys. 2016, 12, 484.A. R. Zeradjanin, J. Masa, I. Spanos, R. Schlogl, Front. Energy Res. 2021, 8, 613092.C. Peng, H. Liu, J. Chen, Y. Zhang, L. Zhu, Q. Wu, W. Zou, J. Wang, Z. Fu, Y. Lu, Appl. Surf. Sci. 2021, 544, 148897.X. Zheng, Y. Chen, X. Zheng, G. Zhao, K. Rui, P. Li, X. Xu, Z. Cheng, S. X. Dou, W. Sun, Adv. Energy Mater. 2019, 9, 1803482.Y. Deng, B. S. Yeo, ACS Catal. 2017, 7, 7873.D. Wang, J. Zhou, Y. Hu, J. Yang, N. Han, Y. Li, T.‐K. Sham, J. Phys. Chem. C 2015, 119, 19573.K. A. Stoerzinger, W. T. Hong, E. J. Crumlin, H. Bluhm, Y. Shao‐Horn, Acc. Chem. Res. 2015, 48, 2976.J. Y. C. Chen, L. Dang, H. Liang, W. Bi, J. B. Gerken, S. Jin, E. E. Alp, S. S. Stahl, J. Am. Chem. Soc. 2015, 137, 15090.J. Gao, C.‐Q. Xu, S.‐F. Hung, W. Liu, W. Cai, Z. Zeng, C. Jia, H. M. Chen, H. Xiao, J. Li, Y. Huang, B. Liu, J. Am. Chem. Soc. 2019, 141, 3014.K. Zhu, X. Zhu, W. Yang, Angew. Chem., Int. Ed. 2019, 58, 1252.

Journal

Advanced Energy Materials – Wiley

Published: Sep 1, 2022

Keywords: electrocatalytic water oxidation; electronic structure; lattice oxygen activation; lithium metal oxides; surface reconstruction

References