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

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Regulating competitive reaction pathways to direct the selectivity of electrochemical CO2 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, Cu3SbS4 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 Cu3SbS4 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 Cu3SbS4 as double‐active sites facilitates the adsorption of *COOH, and thus results in the high selectivity of Cu3SbS4 toward CO.