A mathematical model and optimization of the structure for porous air electrodes

Abstract

A mathematical model for porous air electrodes is developed to optimize the structure of the electrode. The electrode consists of two layers; a gas-supplying layer and a reaction layer. The reaction layer is assumed to consist of porous catalytical agglomerates surrounded by a hydrophobic gas-supplying zone, which is made from the same material as the gas-supplying layer. It is assumed in the model that these agglomerates have a cylindrical shape. The model takes into account the diffusion of oxygen in the gas-supplying layer, the diffusion of dissolved oxygen, the electrochemical reactions taking place, ionic ohmic drop in the cylinder and also electronic ohmic drop due to the finite conductivity of solid material.

To calculate a polarization curve altogether 13 parameters must be known; four geometrical parameters, six parameters which are characteristic of the electrode and three parameters which determine the experimental conditions. The performance of the air electrode is calculated for different geometries and the optimum geometry is determined. In order to simulate a real air electrode the characteristic parameters are measured. Comparisons have also been made between calculated and measured polarization curves.