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 (eCO2RR) is of major interest for generating commercially important C2 liquid products such as ethanol. Cu is exclusive among the eCO2RR 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‐CuxCdy) 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. Needs more ethanol: A series of sulfide‐derived (SD) CuxCdy catalysts are designed for enhancing ethanol selectivity in the electrochemical reduction of CO2. Among them, the SD‐CuCd2 catalyst with a high density of phase boundaries increases the selectivity for conversion of CO2 to ethanol with a faradaic efficiency of 32 % at a low overpotential of 0.89 V. The roles of electrochemically stable CdS in tuning the product selectivity are elucidated.