(342an) Electronic Structure Modeling of Electric Field Driven Catalysis and Electrocatalytic Kinetics

Agrawal, N. - Presenter, Pennsylvania State University
Janik, M. J., Pennsylvania State University
Presence of charge separation in catalytic microenvironments can induce strong electric fields at microscopic length scales. Reaction chemistries involving polar transition states can be strongly influenced by such molecular scale electric fields. In addition, the involvement of polar solvent molecules can further enhance such effects and alter the mechanisms/selectivity of a complex reaction system. Electronic structure methods, including density functional theory (DFT), allow us to examine elementary step reaction trajectories and the redistribution of electrons along a reaction path. Given the value of the electric field(F) and the reaction trajectory, the effect of fields on barriers can be estimated by the differential dipole-field stabilization (ΔμF) without requiring a charged surface simulation. 2nd order effects can be included by additionally estimating the polarizability(∂μ/∂F) through applied field calculations. However, tuning/understanding these electric fields on a microscopic scale to benefit catalysis require fundamental understanding of correlation between externally tunable variables (e.g., applied potential, type of solvent, type of surface, etc.) and the microscopic fields and models to explore the possibilities in the reaction environments.

Electrochemical systems are notoriously challenging for modelling these influences due to presence of a micro-scale charge separation, referred to as the interfacial double layer, with the dual impact of solvation and electric field effects. Approximations are needed to efficiently address these influences computationally. With a Helmholtz model, the magnitude of these electric fields can be related directly to applied bias and approximate width of double layer and the potential of zero charge. However, these estimates are clearly dependent on the choice of model parameters (width of double layer, potential of zero charge and parameters in an explicit/implicit solvation model). Therefore, testing the sensitivity of activation barrier estimates to these parameters and their correlation is essential to making mechanistic conclusions. In this poster, we will share results on the field sensitivity of barrier estimates with a series of electrochemical interface models, and apply these to examine elementary reactions relevant to the oxygen reduction reaction, ammonia electrosynthesis, and carbon dioxide electro-reduction.