Electrochemical CO2 Reduction at Silver from a Local Perspective

The electrochemical reduction of CO2 to chemical fuels and value-added chemicals is a viable pathway to store renewably generated electrical energy and to mitigate the negative impact of anthropogenic CO2 production. Herein, we study how the local reaction environment dictates the mechanism and kinetics of CO2 reduction to CO at an Ag electrode. The local reaction environment is determined using a hierarchical model that accounts for multistep reaction kinetics, specific surface charging state at a given electrode potential, and mass transport phenomena. The model reveals vital mechanistic insights into the reaction behavior. The increasing Tafel slope with overpotential is seen to be influenced by the surface charging relation and mass transport effects. In addition, the decrease of the CO current density at high overpotentials is found to be caused not only by the decrease in CO2 concentration due to mass transport, surface charge effects, and pH increase but also by lateral interactions between HCOOad, COOHad, and Had. Moreover, we explore how the electrolyte properties, including bicarbonate concentration, solvated cation size, and CO2 partial pressure, tune the local reaction environment.