Structural and Electrochemical Studies on the Depolarizability of Manganese Dioxides

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The fundamental reseach on the depolarizability of manganese dioxide has been developed during the past two years. The objectives in this series of experimental and theoretical works are;(1) to understand the "depolarizability" of manganese dioxide both in aqueous and nonaqueous cells in terms of the theoretical electrochemistry combined with structural inorganic chemistory, and(2) to establish some fundamentals on the redox electrochemistory of materials in electrochemical systems, which include the soluble transition metal ions and the organic compounds together with the mixed valence inorganic compounds.Specific experimental and theoretical works done are;(1) a study on the homogeneous electrochemical reaction of manganese dioxide, which recognized as an ideal S-shaped potential curve in the potential vs. the reduction degree plots, and(2) a study on the distorted S-shaped potential curve of L-niobium pentoxide in lithium nonaqueous cell.In order to support these studies, the electrochemical behaviors of the transition metal ions in an acid solution and of the organic compounds in a nonaqueous solution were also examined and the redox properties of materials were specified in terms of electron donor and acceptor.Topotactic reductions of manganese dioxide and L-niobium pentoxide were confirmed by ex-situ X-ray diffraction studies and the reaction mechanisms were proposed. A theory to explain the potential curves of some mixed valence compounds were developed on the basis of statistical thermodynamics, in which the roles of charge charriers in a solid matrix on the electrochemical reaction were emphasized.