A Mathematical Model for the Performance of Raney Metal Gas Diffusion Electrodes

A mathematical model is developed to examine the effect of intragrain diffusion on the operation of Teflon-bonded Raney metal gas diffusion electrodes. The model is based on the concept of “electrolyte flooded spherical catalyst grains” while the gas is filling the space between grains. Analytical equations are derived to evaluate the performance of a single catalyst grain in the presence of diffusion limitations. By incorporating the current generation expression for each grain into the differential equation of potential distribution, complete electrode performance under the combined influence of diffusion, activation, and ohmic overpotentials is predicted. This model is used to predict the polarization behavior of electrodes in terms of physically measurable properties such as exchange current density (intrinsic activity of catalyst), grain size, macroporosity and microporosity, specific surface area, catalyst loading (per unit surface area) and electrode thickness. Model equations are applied to a typical alkaline oxygen electrode, and the results are discussed in combination with the assumptions made in the model.