Activation Energy at Zero Overpotential (E_a⁰) a Thermokinetic Descriptor of Intrinsic Electrocatalytic Activity

Electrochemical water splitting is a key method for sustainable hydrogen production that entails two steps: the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, the slow kinetics of the OER are a significant challenge, limiting its efficiency and impeding its large-scale industrial implementation. There have been many efforts to develop nonprecious electrocatalysts; however, performance assessments often rely on extrinsic metrics (i.e., overpotential, Tafel slope) and may not adequately represent intrinsic electrocatalytic activity. While parameters related to intrinsic activity, such as specific activity and turnover frequency (TOF) are better representations of catalyst performance metrics, yet are limited by uncertainties in measuring the electrochemically active surface area (ECSA). As such, we propose using the activation energy (E_a), specifically E_a⁰, which is described as the activation energy at zero overpotential, as a more fundamental descriptor of intrinsic electrocatalytic activity. E_a⁰ is purely a thermokinetic constant, which is representative of the true energetic barrier under equilibrium conditions, and advantageously does not incorporate contributions of mass transport, iR drop, or applied bias. We propose utilizing a thermokinetic descriptor, such as E_a⁰ to more accurately and fundamentally compare catalyst performance in water-splitting systems.