Analysis of Porous Electrodes with Sparingly Soluble Reactants II . Variable Solution Properties, Convection, and Complexing

The galvanostatic operation of flooded porous electrodes employing metal/metal salt couples is analyzed. A model is developed for a single, circular pore configuration which accounts for the effects of differing equivalent volumes of the solid reactants. The Cd/Cd(OH)/sub 2/ couple in concentrated aqueous potassium hydroxide and the Ag/AgCl couple in concentrated potassium chloride solutions are considered. Overpotential is computed as a function of time for solid-film and solution-diffusion versions of the model. The solid film model shows a linear overpotential-time relationship and nearly uniform current distribution. The solution-diffusion model shows a variety of overpotential-time curves, based on different physical parameters. In general, anodic failure is caused by blockage of pores or by complete coverage of the metal surface by product crytallites. Cathodic failure is caused by low mass transport which leads to limiting currents in the electrode. 41 references.