Journal of Solid State Electrochemistry

Lloris, J.; León, B.; Pérez Vicente, C.; Tirado, J.; Womes, M.; Olivier Fourcade, J.; Jumas, J.

doi: 10.1007/s10008-004-0532-ypmid: N/A

In order to gain a better understanding of the parameters affecting the capacity and performance of spinel electrode materials, the chemical composition and cation distribution of three members of the LiCu x Mn2−x O4 and LiCu0.5−y Al y Mn1.5O4 series have been studied by chemical analysis, X-ray diffraction and X-ray absorption spectroscopy. The synthesis used stoichiometric and lithium-excess precursors. The results evidence that lithium is always incorporated in lower contents than expected from the nominal stoichiometry, owing to the occurrence of significant amounts of copper in the tetrahedral sites of the structure. Manganese displays an oxidation state below 4+ in all these solids, while the lithium-excess synthesis leads to a slightly higher average oxidation state. The electrochemical results evidence the lack of improvement in capacity by using lithium-excess synthesis, while a significant increase in capacity is obtained by aluminium doping, reaching values of 100 mAh/g.

Ambrosio, Renato; Ticianelli, Edson

doi: 10.1007/s10008-003-0474-9pmid: N/A

This is a study of the alloy structure, cycling life, and reaction kinetics of LaNi4.7−x Sn0.3Pt x (x=0 and 0.1) metal hydride electrodes, using X-ray diffraction, X-ray absorption spectroscopy, electrochemical charge/discharge cycling, and electrochemical impedance spectroscopy. It is seen that the presence of platinum in the alloy causes an increase of the cycle life and a decrease in the hydrogen equilibrium pressure, activation time, charge storage capacity, and the rate of capacity decay during multicycling. XANES results are consistent with a decrease in the Ni oxidation in the Pt-containing alloy after the electrode cycling, indicating a protection introduced by Pt against Ni oxidation. It was also found that the catalytic activity of charge/discharge is improved with Pt alloying, a factor exclusively related to an increase of the active area due to higher alloy pulverization.

Wu, Ping; Cai, Chenxin

doi: 10.1007/s10008-003-0481-xpmid: N/A

A new electroactive polynuclear inorganic compound of a rare earth metal hexacyanoferrate, samarium hexacyanoferrate (SmHCF), was prepared chemically and characterized using techniques of FTIR spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction, UV–Vis spectrometry and X-ray photoelectron spectroscopy (XPS) etc. The cyclic voltammetric behavior of SmHCF mechanically attached to the surface of graphite electrode was well defined and exhibited a pair of redox peaks with the formal potential of 180.5 mV (versus SCE) at a scan rate of 100 mV/s in 0.2-M NaCl solution and the redox peak currents increased linearly with the square root of the scan rates up to as high as 1,000 mV/s. The effects of the concentration of supporting electrolyte on the electrochemical characteristics of SmHCF and the transport behavior of K+, Na+ and Li+ counter-ions through the ion channel of SmHCF were studied by voltammetry.

Silva, R.; Francesco, M.; Giorgi, L.; Campa, M.; Cardellini, F.; Pozio, A.

doi: 10.1007/s10008-003-0482-9pmid: N/A

A new method for preparing highly stable Pt–Ru/C catalysts at low temperature is reported. Pt–Ru supported on high surface carbon was prepared from Pt(NH3)4Cl2, RuNO(NO3) x (OH) y and borohydride as a reducing agent. Simultaneous reduction of both metals was done by heat treatment and small and homogeneously dispersed catalyst particles were obtained with increased stability, as observed from solubility tests. Catalysis, XRD and TG data gave clear evidence of the different chemical states between the material produced and the commercially available sample. The electrochemical measurements showed that the novel catalysts have a performance similar to that of E-Tek samples.

Pournaghi-Azar, M.; Nahalparvari, H.

doi: 10.1007/s10008-004-0496-ypmid: N/A

The use of a zinc substrate as an electrode and the modification of its surface by means of a thin film of platinum-doped nickel hexacyanoferrate (Pt-NiHCF) were developed. The modification conditions of the zinc surface including the electroless deposition of metallic nickel on the electrode surface from NiCl2 solution, chemical derivatization of the deposited nickel to the NiHCF film in 0.5 M K3[Fe(CN)6] solution, and electrochemical penetration of metallic platinum into the modified film are described. The modified zinc electrodes prepared under optimum conditions show a well-defined redox couple due to the [NiIIFeIII/II(CN)6]1−/2− system. The effects of pH, the alkali metal cation, and the anion of the supporting electrolyte on the electrochemical characteristics of the modified electrode were studied in detail. The diffusion coefficients of hydrated alkali metal cations in the film (D), the transfer coefficient (α), and the transfer rate constant for the electron (k s) were calculated in the presence of some alkali metal cations. The electrocatalytic activity of the modified electrode for methanol oxidation was demonstrated. The stability of the modified electrode under various experimental conditions was investigated.

Bramnik, Natalia; Bramnik, Kirill; Buhrmester, Thorsten; Baehtz, Carsten; Ehrenberg, Helmut; Fuess, Hartmut

doi: 10.1007/s10008-004-0497-xpmid: N/A

LiCoPO4 samples were synthesized by two different techniques (high-temperature solid-state reaction and lower-temperature synthesis using NH4CoPO4·H2O as precursor) and tested as cathode materials for 5-V lithium batteries. An irreversible lithium deinsertion was observed for the high-temperature sample. In contrast, the application of lower-temperature synthesis led to a significant improvement of the lithium storage reversibility. Different delithiation mechanisms in LiCoPO4 were found for the samples obtained by different synthetic techniques. The nature of capacity fading during cycling of the cells is discussed.

Fetisov, Vadim; Ermakov, Alexander; Belysheva, Galina; Fetisov, Andrey; Kamyshov, Valentin; Brainina, Khiena

doi: 10.1007/s10008-004-0499-8pmid: N/A

The present paper deals with the electrochemical behavior of magnetite microcrystals in an acid medium. A voltammetric method employing a carbon-paste electroactive electrode (CPEE) with an organic binder was used. It was found that the cathodic voltammograms, which were recorded at different scan rates, formed a set bounded in the space of i–E parameters by a “generalizing” voltammetric curve corresponding to the “effective” potential scan rate νeff. In other words, all curves are situated under one enveloping curve, just as the smaller dolls sit in the largest doll of a “Russian doll”. “Reverse” currents (a cathodic current in the anodic direction of the potential scan) were observed on the cyclic voltammogram. Forward and reverse currents obey the same laws and have one and the same “generalizing” curve, which could be taken as the magnetite characteristic.

Shafia Hoor, F.; Ahmed, M.; Mayanna, S.

doi: 10.1007/s10008-004-0501-5pmid: N/A

Electroplating of WO3-Pt has been carried out using a suitable plating bath solution and optimum working conditions. X-ray and SEM studies of the deposit reveal a smooth and uniform distribution of micro-particles on the surface. New phases of the plated material appear on heat treatment. The electrocatalytic activity of the WO3-Pt co-deposit is considerably higher than for platinum alone. WO3 in the WO3-Pt co-deposit reduces the retardation effect of methanol oxidation by the reaction intermediate observed in the case of Pt alone. WO3-Pt co-deposits exhibit low overpotential for methanol oxidation in both acidic and alkaline media at low temperature and have good corrosion resistance in electrolytic media. The electrochemical parameters for methanol oxidation of these co-deposits depend on trace amounts of the platinum, heat treatment and the microstructure of the coating.