Heterostructured Bi-Cu₂S nanocrystals for efficient CO₂ electroreduction to formate

The electrochemical CO₂ reduction reaction (ECO₂RR) driven by renewable electricity holds promise to store intermittent energy in chemical bonds, while producing value-added chemicals and fuels sustainably. Unfortunately, it remains a grand challenge to simultaneously achieve a high faradaic efficiency (FE), a low overpotential, and a high current density of the ECO₂RR. Herein, we report the synthesis of heterostructured Bi-Cu₂S nanocrystals via a one-pot solution-phase method. The epitaxial growth of Cu₂S on Bi leads to abundant interfacial sites and the resultant heterostructured Bi-Cu₂S nanocrystals enable highly efficient ECO₂RR with a largely reduced overpotential (240 mV lower than that of Bi), a near-unity FE (>98%) for formate production, and a high partial current density (2.4- and 5.2-fold higher J_HCOO than Cu₂S and Bi at -1.0 V vs. reversible hydrogen electrode, RHE). Density functional theory (DFT) calculations show that the electron transfer from Bi to Cu₂S at the interface leads to the preferential stabilization of the formate-evolution intermediate (*OCHO).