Sensitivity Analysis of Electrochemical Double Layer Approximations on Electrokinetic Predictions: Case Study for CO Reduction on Copper

Density functional theory (DFT) modeling has been useful to electrocatalyst research, yet simulating the complexities of the electrode-electrolyte interface hinders progress in understanding reaction mechanisms and the underlying kinetics. Though many approaches to incorporating electrochemical double layer (EDL) features in DFT calculations have been developed, uncertainty in interfacial solvent properties and the distribution of ions leave the impact of the EDL on electrocatalytic kinetics unclear. Elucidating the sensitivity of DFT predictions to the EDL properties and model is crucial. Herein, we use an analytical Grand Canonical DFT framework (aGC-DFT) to quantify the sensitivity of potential-dependent activation energies to parameters of the EDL, incorporating a Helmholtz EDL model with varying dielectric constant (ϵ_r) and EDL width (d). We compute the activation barriers for OC-H, CO-H, and OC-CO bond formation from CO* on Cu. These elementary reactions are critical within the heavily debated reaction mechanism of CO₂ reduction and are likely to impact overall activity and product selectivity. We show the aGC-DFT method produces consistent results with explicit GC-DFT calculations, while enabling probing of the EDL model sensitivity at a much lower computational cost. Reaction steps with significant dipole moment changes (i.e., CO-H bond formation) are highly sensitive to the chosen EDL parameters, such that the relative barriers of the OC-H, CO-H, and OC-CO bond formation steps depend significantly on EDL properties. Without knowledge of the interfacial properties of the EDL, there is substantial uncertainty in activation barriers and elementary reaction rates within a DFT analysis of electrocatalytic kinetics.