Theory of galvanostatic processes in mixed conductors with arbitrary electronic transport numbers

Abstract

A detailed analysis of the polarization process in mixed ionic–electronic conductors has been performed, taking into account mixed conductors with arbitrary electronic transport numbers. The mixed conductor is part of an asymmetric electrochemical cell and the polarization process is caused by a constant direct current fed through the cell. Fick's second law of diffusion has been solved by applying the Laplace transform method. In the case of comparable ionic and electronic conductivities, chemical diffusion processes are stimulated at the electronically as well as ionically blocking electrode. The solution function of Fick's second law is therefore given by a superposition of the individual concentration profiles occurring at both electrodes. Time-dependent polarization, as well as depolarization voltages appearing after interruption of the constant current, were calculated for various electronic transport numbers. The influence of the transport numbers leads to additional factors in the mathematical expressions describing the transient voltage response. In addition, the short time behaviour of both the polarization and depolarization voltage was investigated.