Method to Determine the Bifunctional Index for the Oxygen Electrocatalysis from Theory

Abstract

Metal-air batteries are encountered as a promising solution for energy storage due to their high energy density, cost effectiveness, and environmental benefits. Yet, the application of metal-air batteries in practice is still not mature, which is also related to the bifunctional oxygen electrocatalysis at the cathode, comprising the oxygen reduction (ORR) and oxygen evolution (OER) reactions during discharge and charge of the battery, respectively. Experimentally, the performance of electrocatalysts in the OER and ORR is described by bifunctional index (BI), but, so far, there is no direct approach to capture the BI on the atomic scale. Herein, we present a method to ascertain the BI from ab initio theory, thereby combining a data-driven methodology with thermodynamic considerations and microkinetic modeling as a function of the applied overpotential. Our approach allows deriving the BI from simple adsorption free energies, which are easily accessible to electronic structure theory in the density functional theory (DFT) approximation. We outline how our methodology may steer the design of efficient bifunctional catalysts on the atomic scale.