CuSx Catalysts by Ag-Mediated Corrosion of Cu for Electrochemical Reduction of Sulfur-Containing CO2 Gas to HCOOH

Direct conversion of flue gas CO2 emitting from industry to valuable chemicals is an important route for carbon capture and utilization in an economic approach. Flue gas CO2 contains gaseous impurity of H2S at hundreds of ppm levels. However, to date, the effect of H2S on electrochemical catalytic property has rarely been studied. Herein, we investigated the effect of H2S on the morphology, composition, and catalytic activity of thin Ag layers deposited on Cu foil (Ag/Cu) for the electrochemical reduction reaction of modeled sulfur-containing CO2 (CO2 + H2S). The bimetallic Ag (3 nm)/Cu spontaneously changed to CuSx nanostructures during the sulfur-containing CO2 reduction reaction. Ag initially transformed to AgSx with a nanoporous structure, leading to exposure of underlying Cu surface to the electrolyte. Then, the Cu dissolved preferentially because the difference in the reduction potential between Cu and Ag drives the Ag-mediated corrosion reaction. The dissolved Cu ions readily react with sulfur species in the electrolyte, thereby resulting in the formation of thick CuSx nanostructures at the surface. Together with the facilitated charge-transfer activity and increased electrochemical surface area, CuSx nanostructures on Ag (3 nm)/Cu showed higher FEHCOOH = 87.37% (±1.7%) at −0.6 VRHE and jHCOOH = 9.60 (±1.1) mA/cm2 at −1.2 VRHE compared to that of CuSx on Cu foil [FEHCOOH = 69.09% (±2.0%) and jHCOOH = 4.78 (±0.6) mA/cm2]. This study elucidates the origin of galvanic corrosion of bimetallic catalysts and their beneficial effect on the catalytic activity for sulfur-containing CO2 conversion.