Using Sorbitol as Electrolyte Additive to Control Interfacial Environments in Electrochemical CO₂ Reduction on Silver

Abstract

The utilization of electrolyte additives in the electrochemical reduction of CO₂ (CO₂RR) is an effective way to attenuate the hydrogen evolution reaction and increase the yield of carbon-based products. Frequently, the beneficial additive effects can only be demonstrated in batch cell experiments, and the molecular mechanisms behind the observed effects are unclear. Herein, we investigate the impact of sorbitol as an electrolyte additive in the CO₂RR using practically relevant gas diffusion electrodes (GDE) with silver nanoparticles as catalyst, while gaining insight into the reaction mechanisms by molecular dynamics (MD) simulations. The addition of 100 mM sorbitol to the aqueous electrolyte resulted in a notable enhancement of the CO faradaic efficiency, rising from 79% to 90%, while concurrently minimizing the hydrogen evolution reaction (HER) from 15% to 5% at a current density of 98 mA·cm⁻². MD simulations were employed to investigate changes in the electrode/electrolyte interface composition. The addition of sorbitol resulted in a decrease in the concentrations of bicarbonate ions near the electrode interface, while no significant variations were observed for water and CO₂ concentrations. Stronger coordination was observed between potassium ions and CO₂ molecules due to the presence of sorbitol. This interaction may stabilize the CO intermediates and enhance the CO₂RR efficiency. As bicarbonate can be an important intermediate for HER, its reduced concentration is benefiting CO₂RR. This study is a rare example of how a nonionic electrolyte additive such as sorbitol can influence the structure of the solid/liquid interface in electrocatalysis and enhance the performance in CO₂RR.