Electrochemical preparation of cobalt oxide using an autoclave electrolytic cell
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Electrochemical preparation of cobalt oxide using an autoclave electrolytic cell Michio Koinuma,a) Tomohiko Hirae, and Yasumichi Matsumoto Department of Applied Chemistry, Faculty of Engineering, Kumamoto University, Kurokami 2-39-1, Kumamoto 860, Japan (Received 8 September 1997; accepted 5 January 1998)
Polycrystalline films of cobalt oxides (Co3 O4 and CoOOH) with and without Sm were fabricated on platinum substrates by electrochemical oxidation in an autoclave. The cobalt oxides were directly crystallized at temperatures higher than about 100 ±C during electrolysis. The composition of the cobalt oxides strongly depended on the electrode potential; i.e., Co3 O4 and CoOOH were formed in non-noble and relatively noble potential regions, respectively. When Sm was incorporated in the CoOOH by the electrolysis in solutions containing Sm3+ , only the c lattice constant was increased due to an expansion in the layer structure.
I. INTRODUCTION
LnCoO3 and LnMnO3 (Ln: lanthanide ions) are important materials that are used as oxidation catalysts and electrocatalysts. They are especially suitable as the air electrode material for high temperature solid oxide fuel cells because of their chemical stability at high temperature and their superior electrocatalytic properties. Therefore, some preparation methods for the thin films of LnCoO3 and LnMnO3 have been studied.1,2 We have developed a new preparation method for these films using electrochemical oxidation, where the perovskite precursors can be prepared by the electrochemical deposition of the oxyhydroxide or oxide in solutions containing both the transition metal and lanthanide ions.3–7 In our studies of the electrochemical oxidation, it was found that lanthanide ions strongly suppress the electrodeposition of CoOOH and MnO2 by incorporation into the deposits during the deposition.3–8 This suppression effect on the electrodeposition is very strong for the case of CoOOH compared with MnO2 . It was suggested from the analysis of hydration number that the suppression effect is strongly related to the intercalation of Ln3+ ions into the CoOOH layer structure.9,10 However, this intercalation has not been clearly confirmed until now because of the amorphous nature of the deposited CoOOH. It is known that the crystallization occurred for some complex oxides during their electrolysis, when the electrolysis is carried out in an autoclave providing high temperature conditions.11–14 The crystallized CoOOH and Co3 O4 films can also be prepared by the same electrolysis method, although the relationship between the formation of these oxides and the electrolysis cona)
Author to whom correspondence should be addressed. J. Mater. Res., Vol. 13, No. 4, Apr 1998
http://journals.cambridge.org
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ditions is not clear. In this paper, this relationship is demonstrated, and the expansion in the lattice constants of the CoOOH by Sm ion incorporation is reported. II. EXPERIMENTAL
A platinum plate (surface area: 2 cm2 ) was u
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