Electrocatalysis in Water Electrolysis

Abstract

In a recent publication, generation of active surface sites by the overpotential was described as a common pattern in fuel cell electrocatalytic processes [1]. This paper discusses the applicability of the same pattern to the electrocatalytic processes in the water electrolyzer . A wide variety of electrocatalytic processes taking place at either functionalized surfaces , oxide surfaces ,or “metal” surfaces, are all , in fact, surface redox mediated . This means that the electrode potential defines the steady state population of active sites ,suggesting that the role of the potential in active site generation must be incorporated in the pre-exponential factor of the overall rate expression. In fact, the potential driven active site generation serves to “ignite” the faradaic process. This explains why the E0 redoc system of M/MOx , or MOx+n/MOx+n+m surface couples , must be as close as possible to E0 cell process , to enable high conversion efficiency as well as higher rates at low overpotentials. It will be shown here, that, consideration of this general pattern/mechanism of electrocatalytic processes, facilitates understanding of the relative activities of various OER electrocatalysts ,in either acid or alkaline environments. The Pourbaix diagram, provides good insight into the expected relative activities in these, surface redox mediated electrocatalytic processes, together with the other important information regarding expected relative stabilities in acid and in alkali. [1] Shimshon Gottesfeld , ECS Trans. 2014 61(31): 1-13