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

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.