CdS-Enhanced Ethanol Selectivity in Electrocatalytic CO₂ Reduction at Sulfide-Derived Cu-Cd

The development of Cu-based catalysts for the electrochemical CO₂ reduction reaction (eCO₂ RR) is of major interest for generating commercially important C₂ liquid products such as ethanol. Cu is exclusive among the eCO₂ RR metallic catalysts in that it facilitates the formation of a range of highly reduced C₂ products, with a reasonable total faradaic efficiency but poor product selectivity. Here, a series of new sulfide-derived copper-cadmium catalysts (SD-Cu_x Cd_y ) was developed. An excellent faradaic efficiency of around 32 % but with a relatively low current density of 0.6 mA cm^-2 for ethanol was obtained using the SD-CuCd₂ catalyst at the relatively low overpotential of 0.89 V in a CO₂ -saturated aqueous 0.10 m KHCO₃ solution with an H-cell. The current density increased by an order of magnitude under similar conditions using a flow cell where the mass transport rate for CO₂ was greatly enhanced. Ex situ spectroscopic and microscopic, and voltammetric investigations pointed to the role of abundant phase boundaries between CdS and Cu⁺ /Cu sites in the SD-CuCd₂ catalyst in enhancing the selectivity and efficiency of ethanol formation at low potentials.