Theory and kinetic modeling of electrochemical cation-coupled electron transfer reactions

A simple Hamiltonian Marcus-type model for cation-coupled electron transfer reactions is introduced, and an expression for the activation energy is derived. The expression is mathematically similar to the classical Frumkin correction. The model explains how cations lower the activation energy for the Volmer reaction in alkaline media and how cations help stabilizing the first intermediate in electrochemical CO 2 reduction. The second part of the paper introduces the cation effect in a more empirical way in an effective rate law and shows how coupling to local pH changes and the corresponding interfacial cation concentration leads to deviations from the standard Butler-Volmer behavior and to non-linear Tafel plots.