Electro-catalysis for H₂O oxidation

Abstract

Electrocatalysts facilitate two fundamental processes – electron transfer and chemical bond formation/rupture – to convert renewable electrical energy into chemical fuels. Doing so requires the protons and electrons supplied by the oxygen evolution reaction. The reaction steps constituting the oxygen evolution reaction are assumed to result in an electrochemical mechanism qualitatively distinct from the purely chemical ones familiar from thermal catalysis. Such an electrocatalytic mechanism is often thought to be well-described by an exponential dependence of rate on applied overpotential, Tafel’s law, requiring the electrochemical bias to act directly on the reaction coordinate. The aim of the ECHO project has been to test this assumption for the oxygen evolution reaction by combining experimental efforts with density functional theory based modeling of the electrified solid/liquid interface for an important class of electrocatalysts, iridium (di)oxide. Leveraging the computing power of Hawk enabled the use of computational models with explicit solvent to compute realistic surface phase diagrams of IrO₂ and test its role on the kinetics of the oxygen evolution reaction on those surfaces under fixed bias and fixed charge conditions. The results suggest the oxygen evolution reaction is mediated by oxidative charge rather than the action of the electrochemical bias on the reaction coordinate.