Entropy–Enthalpy Compensation in Electrocatalytic Rates

Abstract

Measuring the temperature dependence of electrocatalytic reaction rates is a powerful, yet underexplored, way of investigating the underlying kinetics. In this study, we develop the understanding behind such kinetic measurements. Through a very simple model of the surface kinetics for the hydrogen evolution reaction (HER), we explore how extracted Arrhenius parameters depend on potential and rationalize a series of entropy-enthalpy correlations in experimental HER rates. We find that the entropy-dependent prefactor can change alongside the apparent activation energy, thus signaling deviations from the established Butler-Volmer kinetics that have so far mostly been attributed to potential-driven solvent dynamics. Distinct kinetic fingerprints emerge for different groups of metal catalysts that are in qualitative agreement with recent experiments. We elucidate these characteristic fingerprints in terms of shifting kinetic regimes and generalize our findings to other electrocatalytic reactions and setups. Our analysis overall suggests the entropy loss/gain due to species’ adsorption/desorption as the main driver behind measured changes in the Arrhenius prefactor.