Potential Effects on the Catalytic Mechanisms of OER and ORR

A fundamental understanding of the catalytic mechanisms of the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) at applied electrode potentials is crucial for designing bifunctional catalysts. Here, we revisit the OER and ORR on single-atom catalysts (SACs) by using the grand canonical fixed-potential method. It is revealed that the charge states of reaction intermediates are linearly related to the potential through the capacitance and surface area, and different intermediates exhibit different charge states under the same potential, which arises from the adsorption-induced change in the work function and surface dipole. As a result, the charge transfer in each proton-coupled electron-transfer step is no longer 1e^-, yielding a deviation of the potential-dependent relative free energy from the simple expression with a linear potential correction as in the conventional computational hydrogen electrode model, further affecting the evaluation of overpotential and catalytic activity. Importantly, the slopes of universal scaling relations decrease linearly with increasing electrode potential, resulting in distinct scaling relationships for the OER and ORR. These findings highlight the key role of the potential effects on the OER/ORR and update the understanding of the catalytic mechanisms and catalytic activity trends under working potential.