Regulating *OCHO Intermediate Adsorption via Bi–Sn Orbital Interaction-Induced Electronic Synergy for Selective CO ₂ -to-Formate Conversion

Bi exhibits weak *OCHO intermediate adsorption, limiting its catalytic efficiency and requiring further optimization. Herein, an electronically tunable Bi-Sn bimetallic catalyst (denoted as Bi-Sn) was prepared. The electron-donating Bi and electron-accepting Sn undergo significant electronic reconstruction, which effectively stabilizes the *OCHO intermediate to promote formate selectivity. As a result, Bi-Sn accomplishes a high formate Faradaic efficiency (FE) of 93.4% at -0.8 V vs RHE while maintaining selectivity above 80% from -0.7 to -1.0 V vs RHE. XPS analysis reveals a positive binding-energy shift of Bi³⁺ and a negative shift of Sn⁴⁺ in Bi-Sn compared to pure Bi and Sn, confirming electron transfer from Bi to Sn. Furthermore, the PDOS results of Bi-Sn show significant overlap between the Bi-p and Sn-p orbitals, thereby indicating strong orbital hybridization to facilitate charge transfer. In addition, charge-density difference calculations demonstrate remarkable electron redistribution between Bi and Sn, thus stabilizing *OCHO adsorption. This electronic synergy strategy effectively strengthens *OCHO binding (ΔG*OCHO = -0.27 eV) while suppressing H adsorption (ΔG*H = 2.9 eV), thereby accelerating CO₂ electroreduction toward formate. Hence, the orbital-overlap-induced Bi/Sn electronic synergy may provide rational guidance for designing high-performance CO₂RR catalysts.