Influence of pH and Proton Donor/Acceptor Identity on Electrocatalysis in Aqueous Media
Vincent J. Ovalle, Matthias M. Waegele
Abstract
Understanding the effects of solution pH on the rates and mechanisms of multiproton/electron transfer reactions at aqueous electrolyte/electrode interfaces has been an active area of research for many decades. Recent interest in this topic has been driven by observations that the reaction selectivity and rates of electrocatalytic processes for energy storage and renewable fuel synthesis can profoundly change with electrolyte pH. Further, a subset of these reactions, such as CO and CO2 reduction, are often carried out under near-neutral bulk pH conditions. Such conditions, in combination with insufficient mass transport and limited pH buffer capacity, can lead to substantial deviations of the near-electrode pH from the bulk pH of the electrolyte. Such pH gradients, together with electrodes whose surface chemistry is highly dependent on pH, can give rise to complex feedback between the reactions that are catalyzed on the surface and the local pH conditions and surface speciation. In this Perspective, we discuss representative studies that characterize and quantify the effects of (local) pH on electrocatalysis with innovative experimental and theoretical methods. We further highlight possible future directions of investigation.