Enhanced formate production from sulfur modified copper for electrocatalytic CO₂ reduction

Producing liquid fuels with high selectivity and low overpotential has long been a goal of electrocatalytic CO₂ reduction reaction (CO₂RR). Here we present a detailed study on the structural and catalytic properties of sulfur on copper for CO₂RR. Cu₂S was formed by enabling sulfur to deposit on the copper surface with a simple surface impregnation method. The sulfur modified samples, especially the sulfur modified oxide-derived copper (SM-OD-Cu), have significantly higher selectivity to formate than the pure and oxide-derived copper. At a potential range of −0.51∼−0.75 V vs. RHE, the selectivity of formate for SM-OD-Cu in the liquid phase was nearly 100 %. Also, the partial current density of formate reached −4.26 mA/cm² at −0.75 V vs. RHE. By using density functional theory calculation, we found that Cu₂S significantly inhibits the CO pathway and hydrogen evolution reaction, and further improves the selectivity of formate.