(265d) Development of Models for Calculation of Elementary Electrochemical Activation Barriers with Density Functional Theory

Density Functional Theory (DFT) calculations have been useful in predicting the kinetics and reaction mechanisms for heterogeneous catalytic systems. However, the utility of DFT calculations is challenged in modelling electrocatalytic systems due to the complex and system-specific nature of solvation and electrode-electrolyte electrification effects near the electrode surface. Performing a dynamic explicit quantum mechanical simulation of the interface becomes computationally prohibitive due to the correlation length and time scales of solvent near the electrified surface. Therefore, approaches to study kinetics employ approximations in representing the solvent effects and the electric fields near the electrode surface. Quantifying the imprecision introduced due to modeling approximations, and appreciation of the extent to which trends among catalysts or reaction steps are preserved despite these imprecisions, becomes critical.

In this talk, we will discuss several model approximations employed to include solvation and electrification towards evaluation of elementary electrochemical activation barriers. Solvation approaches considered will include micro-solvation with a few explicit water molecules as well as continuum solvation approaches. We will discuss the impact of the assumed bulk dielectric constant as well as other computational parameters (e.g., cutoff electron density) on calculated elementary activation barriers. Electrification will be examined with both applied external electric fields and implicit double-layer charging with continuum electrolyte to demonstrate the sensitivity of these modelled interfacial features towards quantitative barrier estimates. Example elementary reactions relevant to the oxygen reduction reaction, ammonia electrosynthesis, and carbon dioxide electro-reduction reaction will be discussed.