Quantum Theory of the Metal Dependence of Electrocatalysis

The quantum theory of coupled ion-electron transfer (CIET) unifies phenomenological Butler–Volmer kinetics with the Marcus theory of electron transfer in a single, thermodynamically consistent modeling framework for Faradaic reaction rates. Here, we extend CIET theory to explicitly incorporate the electronic properties of the electrode to highlight the direct influence of electrode quantum physics on reaction kinetics. For electrocatalytic reactions limited by ion transfer, the modified formulation for “ion-coupled electron transfer” (ICET) predicts Butler-Volmer kinetics with an exchange current density having an Arrhenius dependence on the electrode’s work function times the anodic charge-transfer coefficient. Notably, this formulation alters reaction rates via the electron concentration, which is controlled by the electrode’s Fermi energy and the reaction plane’s surface potential relative to those of the reference electrode, without changing the Nernst equilibrium potential of the redox couple. The theory predicts experimental trends in the rates of the hydrogen evolution reaction (HER) in acid and aqueous iron redox reactions on different metals, while also capturing the volcano dependence on adsorption free energies. CIET theory thus provides a convenient basis for the design of electrocatalytic interfaces, combining insights from molecular simulations and experimental characterization.