(169a) A Density Functional Theory Approach to Electrocatalytic Reaction Barriers

The activity and selectivity of electrocatalysts is dictated by the activation barriers of elementary reaction steps. These elementary steps are often a combination of chemical and electrochemical steps, where electrochemical steps involve the transfer of ions from/to the electrolyte and electrons from/to the electrode. Though density functional theory methods have frequently been applied to investigate elementary reaction (free) energies within electrocatalytic reactions, the calculation of barriers for elementary electrochemical steps is less frequent. It is challenging to represent the electrochemical nature of these reactions, as transitioning from an ion in the bulk of the electrolyte to a reaction event at the surface challenges the length and time scales accessible with typical DFT models. In this talk, I will give an overview of methods currently in the literature to consider electrocatalytic reaction barriers, and review a simple and transferable approach we have developed and applied. Our approach uses DFT calculations on analogous non-electrochemical reactions (ie. hydrogenation) to define transition state structures and a reaction coordinate that can be used to determine electrode-potential dependent barriers for equivalent electrochemical reactions (ie. proton and electron transfer). The non-electrochemical transition state is referenced rigorously to the bulk phase ion and electron chemical potentials. Approaches within a Marcus Theory framework to determine the potential dependence of barriers will be discussed, with application to elementary steps involved in N₂ reduction, CO₂ reduction, and furfural oxidation.