Understanding the mechanism of electrode overvoltage generation is important for development of functional new all-solid-state electrochemical devices. The theory of electrode overvoltage developed for liquid-state electrochemical systems led to ambiguous causality when applied to solid-state systems. In this paper, the solid-state overvoltage is formulated from ionic transport theory in solids. The solid-state device was treated as an inhomogeneous thermodynamic system. Overvoltage was derived as a function of entropy production rate and found to be attributable to diffusion of neutral compounds in the electrodes. We discussed (1) measurement of the electrode overvoltage by the current interruption technique; (2) composite electrodes consisting of the electrolyte, electronic conductor, and active material; and (3) the problem on separation of charge transfer reaction process. Physical role of the electrode overvoltage was discussed on the basis of classical irreversible thermodynamics.
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