Disentanglement of interfacial electric fields and electrochemical potential gradients reveals a multidimensional kinetic landscape

Electrochemical reactions occur at solid-liquid interfaces, where the applied electrochemical potential gradient can act as thermodynamic driving force but can also induce interfacial polarization. A key question has long been how local changes in the chemical potentials of the electrons and the associated excess charge and electric fields impact catalyst kinetics. Here we combine temperature-dependent current transients from oxidative CO stripping with a CO coverage-dependent potential of zero total charge and Raman spectroscopy. We observe a reduction of the activation energy with increasing driving force. By contrast, increasing the distance between the applied potential and the potential of zero total charge results in an increase in the apparent activation energy, which we ascribe to an electric field effect in the double layer. More generally, the results demonstrate how interfacial changes in the chemical potentials give rise to a multidimensional kinetic landscape, in which single-descriptor kinetics fail to capture the nature of the overpotential.