Analysis of Porous Electrodes with Sparingly Soluble Reactants

The galvanostatic operation of flooded porous electrodes mploying meta l / 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 model also includes effects of variat ion in solution propert ies and effects of complexing of the sparingly soluble salt with the bulk electrolyte anion. The Cd/Cd (OH)2 couple in concentrated aqueous potassium hydroxide and the Ag/AgC1 couple in concentrated potassium chloride solu-tions are considered. Overpotential is computed as a function of t ime for solid-film and solution-diffusion versions of the model. The solid film model shows a l inear overpotential-t ime relationship and nearly uniform current distribution. The solution-diffusion model shows a var iety of overpotential-t ime curves, based on different physical parameters. In general, anodic fai lure is caused by blockage of pores or by complete coverage of the metal surface by product crystall ites. Cathodic fai lure is caused by low mass transport which leads to