Cu–Sn Bimetallic Catalyst for Selective Aqueous Electroreduction of CO2 to CO

We report a selective and stable electrocatalyst utilizing non-noble metals consisting of Cu and Sn for the efficient and selective reduction of CO2 to CO over a wide potential range. The bimetallic electrode was prepared through the electrodeposition of Sn species on the surface of oxide-derived copper (OD-Cu). The Cu surface, when decorated with an optimal amount of Sn, resulted in a Faradaic efficiency (FE) for CO greater than 90% and a current density of −1.0 mA cm–2 at −0.6 V vs RHE, compared to the CO FE of 63% and −2.1 mA cm–2 for OD-Cu. Excess Sn on the surface caused H2 evolution with a decreased current density. X-ray diffraction (XRD) suggests the formation of Cu–Sn alloy. Auger electron spectroscopy of the sample surface exhibits zerovalent Cu and Sn after the electrodeposition step. Density functional theory (DFT) calculations show that replacing a single Cu atom with a Sn atom leaves the d-band orbitals mostly unperturbed, signifying no dramatic shifts in the bulk electronic structure. However, the Sn atom discomposes the multifold sites on pure Cu, disfavoring the adsorption of H and leaving the adsorption of CO relatively unperturbed. Our catalytic results along with DFT calculations indicate that the presence of Sn on reduced OD-Cu diminishes the hydrogenation capability—i.e., the selectivity toward H2 and HCOOH—while hardly affects the CO productivity. While the pristine monometallic surfaces (both Cu and Sn) fail to selectively reduce CO2, the Cu–Sn bimetallic electrocatalyst generates a surface that inhibits adsorbed H*, resulting in improved CO FE. This study presents a strategy to provide low-cost non-noble metals that can be utilized as a highly selective electrocatalyst for the efficient aqueous reduction of CO2.