Correlating Equilibrium Excess Charge with the Kinetics of the Multi-Step Hydrogen Evolution Reaction in Alkaline Media

Electrocatalytic reactions often proceed over polarizable interfaces in the presence of excess charge and intermediate coverages. However, it is still not well understood how this polarization impacts the electrocatalytic activity. Here, we perform electrochemical Arrhenius- and temperature-dependent Tafel analysis on the hydrogen evolution reaction in alkali in conjunction with CO-displacement measurements. We use the potential of zero total charge as a measure of equilibrium excess charge that we correlate with overpotential-dependent kinetics on Ni-, Co-, and Fe-oxide-decorated polycrystalline Pt foils. Consistent with the literature, we find that the oxide coverage reduces the equilibrium excess charge. However, we also discover that this correlates with a lower transition overpotential between different kinetic regimes. With a microkinetic model, we show that an overpotential-dependent H-coverage and overpotential-dependent rate-limiting steps could explain the Arrhenius trends. Our results further suggest that increasing excess charge at equilibrium might increase the barrier of the Volmer step.