Switching Product Selectivity in CO2 Electroreduction via Cu−S Bond Length Variation

Abstract Regulating competitive reaction pathways to direct the selectivity of electrochemical CO 2 reduction reaction toward a desired product is crucial but remains challenging. Herein, switching product from HCOOH to CO is achieved by incorporating Sb element into the CuS, in which the Cu−S ionic bond is coupled with S−Sb covalent bond through bridging S atoms that elongates the Cu−S bond from 2.24 Å to 2.30 Å. Consequently, CuS with a shorter Cu−S bond exhibited a high selectivity for producing HCOOH, with a maximum Faradaic efficiency (FE) of 72 %. Conversely, Cu 3 SbS 4 characterized by an elongated Cu−S bond exhibited the most pronounced production of CO with a maximum FE of 60 %. In situ spectroscopy combined with density functional theory calculations revealed that the altered Cu−S bond length and local coordination environment make the *HCOO binding energy weaker on Cu 3 SbS 4 compared to that on CuS. Notably, a volcano‐shaped correlation between the Cu−S bond length and adsorption strength of *COOH indicates that Cu−S in Cu 3 SbS 4 as double‐active sites facilitates the adsorption of *COOH, and thus results in the high selectivity of Cu 3 SbS 4 toward CO.