The fundamental drivers of electrochemical barriers

We find that ionization dominates the behavior of electrochemical reaction barriers, through grand-canonical electronic structure calculations of proton-deposition on transition metal surfaces. We show that barriers respond to potential in a nonlinear manner and trace this to the continuous degree of electron transfer as an ion is created or destroyed. This explains both Marcus-like curvature and Hammond-like shifts. Across materials, we find the barrier energy to be driven primarily by the charge presented on the surface, which in turn is dictated by the native work function, a fundamentally different driving force than non-electrochemical systems.