Predicting macro-kinetic observables in electrocatalysis using the generalized degree of rate control

Abstract

Kinetic observables such as the Tafel slope, apparent activation energy, and apparent reaction orders all provide mechanistic fingerprints for electrocatalytic processes. Here, we show how each of these quantities is related to the generalized degree of rate control (DRC). We find that the apparent transfer coefficient, an inverted form of the Tafel slope, is a weighted average of the number of electrons transferred to generate each intermediate or product species in a mechanism, where the weighting factor is the DRC. We similarly show that the apparent activation energy and apparent reaction orders (with potential dependence) can also be written in simple terms of the DRC. Since DRCs can further be related with microscopic quantities such as fractional coverages of intermediates, these relations can be used to improve intuition about possible operative mechanisms of complex electrocatalytic processes. Final discussions address the possible impacts of various nonidealities such as electric field effects, adsorbate interactions, and approximations related to the form of electrochemical rate constants.