Current Distribution in Porous Electrodes Whose Solid Phase's Conductivity Increases from the Rear Current Lead

Abstract

The distribution of the current and the efficiency of porous electrodes (PE) of different types are studied theoretically and experimentally. The conductivity of the solid phase of PE under study is the same or either decreases or increases from the rear current lead. As compared with a homogeneous porous matrix, decreasing the solid-phase conductivity deep into PE improves the PE efficiency by approximately 2.5 times. Conversely, increasing the conductivity deep into PE dramatically degrades the PE efficiency. Simultaneously, the current concentrates near edges of PE and an anodic zone emerges inside PE. As a result, dependences of the effective working thickness of PE and the current efficiency for the target reaction on the total current density acquire a characteristic form, with a maximum and a subsequent decay to zero, even up to a change in the sign. Qualitatively similar form of such dependences is observed experimentally during cathodic reduction of K3Fe(CN)6on PE comprising three layers of carbon felts with gradually increasing conductivities.