Crystalline CdS/Amorphous Cd(OH)₂ Composite for Electrochemical CO₂ Reduction to CO in a Wide Potential Window

Electrochemical CO₂ reduction is a promising method for converting atmospheric CO₂ into valuable low-carbon chemicals. In this study, a crystalline cadmium sulfide/amorphous cadmium hydroxide composite was successfully deposited on the carbon paper substrate surface by in-situ chemical bath deposition (named as c-CdS/a-Cd(OH)₂/CP electrodes) for the efficient electrochemical CO₂ reduction to produce CO. The c-CdS/a-Cd(OH)₂/CP electrode exhibited high CO Faradaic efficiencies (>90 %) under a wide potential window of 1.0 V, with the highest value reaching ~100 % at the applied potential ranging from -2.16 V to -2.46 V vs. ferrocene/ferrocenium (Fc/Fc⁺), superior to the crystalline counterpart c-CdS/CP and c-CdS/c-Cd(OH)₂@CP electrodes. Meanwhile, the CO partial current density reached up to 154.7 mA cm^-2 at -2.76 V vs. Fc/Fc⁺ on the c-CdS/a-Cd(OH)₂/CP electrode. The excellent performance of this electrode was mainly ascribed to its special three-dimensional structure and the introduction of a-Cd(OH)₂. These structures could provide more active sites, accelerate the charge transfer, and enhance adsorption of *COOH intermediates, thereby improving the CO selectivity. Moreover, the electrolytes consisting of 1-butyl-3-methylimidazolium tetrafluoroborate and acetonitrile also enhanced the reaction kinetics of electrochemical CO₂ reduction to CO.