Local Reaction Environment Deviations within Gas Diffusion Electrode Pores for CO<sub>2</sub> Electrolysis
Esaar Naeem Butt, Johan T. Padding, Remco Hartkamp
Abstract
The local conditions inside a gas diffusion electrode (GDE) pore, especially in the electrical double layer (EDL) region, influence the charge transfer reactions and the selectivity of desired CO 2 ER products. Most GDE computational models ignore the EDL or are limited in their applicability at high potentials. In this work, we present a continuum model to describe the local environment inside a catalytic pore at varying potentials, electrolyte concentrations and pore diameters. The systems studied in this work are based on an Ag catalyst in contact with KHCO 3 solution. Our study shows that steric effects dominate the local environment at high cathodic potentials (≪−25 mV vs pzc at the OHP), leading to a radial drop of CO 2 concentration. We also observe a drop in pH value within 1 nm of the reaction plane due to electrostatic repulsion and attraction of OH − and H + ions, respectively. We studied the influence of pore radii (1–10 nm) on electric field and concentrations. Pores with a radius smaller than 5 nm show a higher mean potential, which lowers the mean CO 2 concentration. Pores with a favourable local environment can be designed by regulating the ratio between the pore radius and Debye length.