Journal of Solid State Electrochemistry

Grygar, Tomáš

doi: 10.1007/s100080050077pmid: N/A

The electrochemical dissolution of metal oxides and other stable solid phases composed of nano- to micro-crystalline particles is generally a complex process. It can be simplified by distinguishing two main contributions to the reactivity of the solid: the potential-dependent rate coefficient k(E), and the conversion-dependent function f(y). These contributions can be evaluated by a combination of potentiostatic and potentiodynamic experiments. Both k(E) and f(y) were obtained experimentally for the dissolution of iron and chromium oxides, and theoretical consequences of their particular forms are discussed. A peak-shaped function k(E) was observed in the case of γ-Fe2O3, whereas, for α-Cr2O3 and CrO2, a different model based on intermediate surface complexes is proposed. This model also explains the complete electrochemical dissolution of metal oxides regardless of their low intrinsic electric conductivity.

Larcher, Dominique; Gérand, Bernard; Tarascon, Jean-Marie

doi: 10.1007/s100080050078pmid: N/A

The spinel phases Li1+ y Mn2− y O4 have been synthesized by a novel synthesis method that presents advantages compared to the classical ceramic method, namely, in terms of preparation time, costs and electrochemical performances of the resulting products. This consists of a two-stage process. First, two precursor phases (Li-EG and Mn-EG) are synthesized by reacting powdered lithium hydroxide and electrolytic manganese dioxide (EMD) in ethylene glycol (EG) under reflux, respectively. Secondly, the precursor products are mixed and heat treated under air, following various heating sequences, to produce electrochemically active Li1+ y Mn2− y O4 powders of well-defined morphology. Once the synthesis parameters involved in these two steps are controlled, the obtained Li1+ y Mn2- y O4 powders exhibit electrochemical performances that compare favorably with those observed in the case of the high-temperature (HT) Li1+ y Mn2− y O4 made by the ceramic route, both in terms of reversible/irreversible capacities and cycling behavior at 25 °C and 55 °C.

Yaremchenko, Aleksey A.; Kharton, Vladislav V.; Naumovich, Evgeny N.; Vecher, Alim A.

doi: 10.1007/s100080050079pmid: N/A

The minimum concentration of niobium to stabilize the fluorite-type f.c.c. phase in the Bi2O3–Nb2O5 oxide system at temperatures below 996 K was ascertained to be about 10 mol%. Thermal expansion, electrical conductivity and crystal lattice parameters of the Bi(Nb)O1.5+δ solid solutions decrease with increasing niobium content. Thermal expansion coefficients were calculated from the dilatometric data to be (10.314.5)×10−6 K−1 at temperatures in the range 300–700 K and (17.526.0)×10−6 K−1 at 700–1100 K. The conductivity of the Bi1− x Nb x O1.5+δ ceramics is predominantly ionic. The p-type electronic transference numbers of the Bi(Nb)O1.5+δ solid solutions in air were determined to be less than 0.1. Annealing at temperatures below 900 K results in a sharp decrease in conductivity of the Bi1− x Nb x O1.5+δ ceramics.

Proost, Joris; Baklanov, Michael; Verbeeck, Rita; Maex, Karen

doi: 10.1007/s100080050080pmid: N/A

The morphology of corrosion pits in sputtered pure aluminum and Al(0.5 wt% Cu) thin film metallizations has been investigated for a diluted chloride solution. The observed fractal-like patterns show clearly distinct features in ramification and branch density, which can be attributed to microscopic inhomogeneities inside the aluminum film. It is discussed how these observations may have an impact on the current description of diffusion phenomena in thin films, e.g. concerning electromigration.

Moon, Sung-Mo; Pyun Su-II,

doi: 10.1007/s100080050081pmid: N/A

The present work was conducted to explore the growth mechanism of anodic oxide films on pure aluminium in aqueous acidic and alkaline solutions by using a.c. impedance spectroscopy and a beam deflection technique. From the analyses of a.c impedance data, it was found that the reciprocal capacitance of anodic oxide film on pure aluminium increased linearly with increasing film formation potential in both acidic and alkaline solutions, indicating a linear increase in the film thickness with film formation potential. However, as the film formation potential increased, the resistance of anodic oxide film decreased in acidic solution, while it increased in alkaline solution. From the measurements of the deflection, the deflection was observed to move towards only a compressive direction with time in acidic solution, but it showed a transition in the direction of movement from compressive to tensile in alkaline solution. Based upon the above experimental results, it is suggested that the movement of oxygen vacancy through the oxide film contributes to the growth of anodic oxide film on pure aluminium in acidic solution, but the movement of both aluminium vacancy and oxygen vacancy accounts for that oxide film growth in alkaline solution.

Radmilović, V.; Popov, K. I.; Pavlović, M. G.; Dimitrov, A.; Jordanov, S. Hadži

doi: 10.1007/s100080050082pmid: N/A

Granules as a possible form of metal electrodeposit can be formed during deposition of metals, such deposition processes being characterized by large exchange current density values. Because of this, zero nucleation zones around growing grains are formed, permitting granular metal growth. In some cases of prolonged deposition, macro-crystalline deposits can be formed as well as granular ones, e.g. in the case of silver deposition at overpotentials lower than the critical value for dendrite growth initiation. The mechanism of granular deposit growth as a final form of metal electrocrystallization is proposed. Silver boulders were deposited on␣platinum and silver substrates. At low deposition potentials, various crystallographic forms, some of them ideal or derived from cube-octahedron-type morphology, were obtained as a result of independent grain growth inside zones of zero nucleation. In addition to cube-octahedra, twinned and multiply twinned silver particles were also observed. The nucleation density was found (1) to increase with increasing deposition overpotential, (2)␣to decrease with increasing silver concentration, and (3) to be greater on Ag than on Pt for the same deposition overpotential and dendrite precursors. Increasing overpotential leads to increase of density of twinned grains. The grain growth at greater overpotentials from more concentrated solution is less ideal, producing a granular deposit on prolonged deposition.

Khader, Mahmoud M.; Saleh, Mahmoud M.; El-Naggar, Emad M.

doi: 10.1007/s100080050083pmid: N/A

Active ferric tungstate was prepared by fusing an equimolar mixture of tungsten oxide and ferric oxide at 1100 °C and annealing at 800 °C for 20 h. Analysis of the electrode material by X-ray diffraction showed that its composition was Fe2WO6. When this material was illuminated by visible light in 0.1 M NaOH solution, an anodic photocurrent at a positive potential of 0.5 V (SCE) was obtained. Therefore, this material is considered as an n-type semiconductor. The d.c. conductivity of this material at 25 °C was 4 × 10−6 Ω−1 cm−1. In the dark, unexpectedly high anodic currents were observed at positive potentials of 0.8 V (SCE) in 0.1 M NaOH. These currents are attributed to the existence of a high density of electron-hole recombination centers within the band-gap of ferric tungstate. When dimethyl viologen (DMV) was used as an electroactive compound in the electrolyte, the anodic photocurrents increased significantly. The oxidation of DMV is thus expected to compete with the electron-hole recombination process. Furthermore, the process of electron-hole recombination was also predicted from the shape of the photocurrent transients under interrupted illumination. These transients exhibited first-order relaxation effects in the region of the onset time of the photocurrents. The band-gap energy of Fe2WO6 was found to be about 1.5 eV and its flat-band potential in 0.1 M NaOH was about −0.3 V (SCE). The photoelectrochemical properties of ferric tungstate are explained according to the formalism of the band model of the semiconductor/electrolyte interface.

Gurunathan, K.; Maruthamuthu, P.

doi: 10.1007/s100080050084pmid: N/A

Bi5Nb3O15 was prepared from a stoichiometric mixture of Bi2O3 and Nb2O5 at 300–500 °C. The prepared photocatalyst was characterized by diffuse reflection spectrum (DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size analysis. The band gap, crystal structure and average grain size were determined from the above methods to be 3.25 eV, distorted pyrochlore and 4–5 μm respectively. The photoelectrochemical behavior of hydrogen-reduced Bi5Nb3O15 was investigated in 0.1 M Na2SO4 and using the Fe(CN)6 3−/4− redox couple for measuring the current-voltage characteristics. The cyclic voltammetric studies revealed that the onset potential for photocurrent generation existed at −0.45 V, which is more negative to water reduction level at pH 7.0, and that of the photocurrent at 1.0 V was observed as 0.58 mA/cm2. Photocatalytic hydrogen production has been achieved by using Bi5Nb3O15 as a photocatalyst in presence of methyl viologen. The quantum yield for hydrogen production for this system was found to be 0.83. All the studies clearly indicated that Bi5Nb3O15 has potential in solar energy conversion.

Denesuk, Matthew; Uhlmann, Donald R.

doi: 10.1007/s100080050085pmid: N/A

A set of phenomenological analysis tools have been developed for the characterization of the optoelectrochemical behavior of electrochromic intercalation devices. Both step current and step potential excitations are considered. Great simplification is afforded by working with the passed charge as the primary independent variable; consideration is also given, however, to the transmission or built-in device potential as independent variables. It is shown that quasi-static intercalation efficiency curves, generated from step current measurements, can elucidate the intercalation site-energy distribution; these curves are also compared to dynamic intercalation efficiency curves obtained from step potential measurements. Quasi-static and dynamic optical efficiencies are also considered and compared. The scaling properties of some of the phenomenological parameters may be used to generate master curves which unify sets of data obtained under a variety of conditions (applied voltages, imposed currents, film thicknesses, etc.). Quantitative predictions can be made of device behavior under conditions not probed experimentally.

Ureta-Zañartu, M. Soledad; Yáñez, Claudia; Reyes, Gloria; Gancedo, José Ramón; Marco, José F.

doi: 10.1007/s100080050086pmid: N/A

The activity of Pt-Ir deposits on titanium for the reduction of the nitrate ion in 0.5 M perchloric acid was studied. The electrodes were characterized by SEM-EDAX, XPS and cyclic voltammetry. The activity of the electrodes for the nitrate reduction depended on the Pt-Ir ratio. Repetitive cyclic voltammograms produced an enrichment of the electrode surface with Ir and a decrease of the catalytic activity. A synergistic effect in the electrodes with low iridium content is discussed.