Influence of solid phase conductivity on spatial localization of electrochemical processes in flow-through porous electrodes: Part I: Electrodes with uniform conducting matrix

Abstract

Mathematical simulation of the flow-through porous electrode (PE) operation on the basis of a one-dimensional model with a uniform conducting matrix and a cathodic process involving the main and side reactions (i.e., hydrogen evolution) has been made. The influence of current density and rate and direction of the solution flow on the depth of the main process penetration into the PE has been analysed for different relationships between phase conductivities. It has been shown that when the polarization curve of the side reaction is Tafelian, and the rate of solution circulation is high, there is a limit for the main process penetration into the PE. This limiting value is close to the thickness of the layer, Ld, capable of working at the limiting diffusion current obtained by Sioda's method. The dependence of the Ld layer thickness on phase conductivity has been analysed. In the limiting cases (low fractional conversion, high or identical phase conductivities) analytical expressions for Ld have been obtained. At low flow rates, the depth of the main process penetration increases up to the value of the entire thickness of the PE. It can be concluded that the possibility of increasing the PE efficiency for the uniform matrix by changing phase conductivities is limited.