Analysis of Porous Electrodes with Sparingly Soluble Reactants

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 model also includes effects of variation in solution properties and effects of complexing of the sparingly soluble salt with the bulk electrolyte anion. The couple in concentrated aqueous potassium hydroxide and the 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 crystallites. Cathodic failure is caused by low mass transport which leads to limiting currents in the electrode. The solution‐diffusion model may generate extremely nonuniform current distributions, often with maxima inside the pore. These persistent nonuniform current distributions are important in terms of the analysis of cycling behavior.