DIFFUSION-MIGRATION CAPACITANCE IN HOMOGENEOUS MEMBRANES, MODIFIED ELECTRODES AND THIN-LAYER CELLS

Asymmetric cells and modified electrodes with reversible electron exchange at one interface and reversible ion exchange at the other are predicted to show both transport and charge storage pseudocapacitance. The transport capacitance merges the Warburg and cyclic voltammetric d.c. capacitance. This paper covers the primitive charge storage model, the corrections for anion Donnan potential differences and, finally, the whole frequency-dependent capacitance for a simple, one-salt asymmetric redox cell, and the modified electrodes with uninegative anions and a redox polymer with a one-electron redox process. Not surprisingly, when processes at both interfaces are combined, all these cases are nearly the same, with minor modifications. No new theory is required to treat these on the same basis or to derive the frequency-dependent capacitance, sometimes called the transport ''pseudocapacitance''.