In-situ electrochemical restructuring of Cu₂BiS_x solid solution into Bi/Cu_xS_y heterointerfaces enabling stabilization intermediates for high-performance CO₂ electroreduction to formate

Bismuth-based materials are prevalent catalysts for CO₂ electroreduction to formate, enduring high hydrogen evolution reactions and inadequate activity and stability. Herein, we reveal that in-situ electrochemical transformation of Cu₂BiS_x solid solution into Bi/Cu_xS_y heterointerfaces, which can stabilize the intermediates and achieve highly selective and consistent CO₂ electroreduction. It shows over 85% Faraday efficiency (FE) of formate with a potential window of −0.8 to −1.2 V_RHE (RHE: reversible hydrogen electrode) and a stability above 90% over 27 h in H-type cell at −0.9 V_RHE. It maintains more than 85% of FE_formate at the current density of −25 to −200 mA·cm⁻², and has stability of about 80% of FE_formate at least 10 h at −150 mA·cm⁻² in flow cell. In-situ Fourier transform infrared (FT-IR) spectroscopy measurement confirms that the preferred route of catalytic reaction is to generate *CO₂⁻ and *OCHO intermediates. The density functional theory (DFT) calculations illustrate that heterointerfaces facilitate the prior process of CO₂ to HCOOH through *OCHO by additional Bi hybrid orbitals. This study is expected to open up a new idea for the design of CO₂ electroreduction catalyst.