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

Direct conversion of flue gas CO 2 emitting from industry to valuable chemicals is an important route for carbon capture and utilization in an economic approach. Flue gas CO 2 contains gaseous impurity of H 2 S at hundreds of ppm levels. However, to date, the effect of H 2 S on electrochemical catalytic property has rarely been studied. Herein, we investigated the effect of H 2 S 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 CO 2 (CO 2 + H 2 S). The bimetallic Ag (3 nm)/Cu spontaneously changed to CuS x nanostructures during the sulfur-containing CO 2 reduction reaction. Ag initially transformed to AgS x 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 CuS x nanostructures at the surface. Together with the facilitated charge-transfer activity and increased electrochemical surface area, CuS x nanostructures on Ag (3 nm)/Cu showed higher FE HCOOH = 87.37% (±1.7%) at −0.6 V RHE and j HCOOH = 9.60 (±1.1) mA/cm 2 at −1.2 V RHE compared to that of CuS x on Cu foil [FE HCOOH = 69.09% (±2.0%) and j HCOOH = 4.78 (±0.6) mA/cm 2 ]. This study elucidates the origin of galvanic corrosion of bimetallic catalysts and their beneficial effect on the catalytic activity for sulfur-containing CO 2 conversion.