Ampere-level CO2-to-formate electrosynthesis using highly exposed bismuth(110) facets modified with sulfur-anchored sodium cations

Summary

The high-rate electrosynthesis of formate from CO₂ is challenging due to the insufficient active catalytic sites that can stabilize the ∗OCHO intermediate and suppress H₂ formation at large-current-density electrolysis. Herein, we developed the metallic bismuth nanosheets with highly exposed (110) facets modified with sulfur anions and sodium cations (i.e., Bi(110)-S-Na). Density functional theory calculations revealed that Bi(110) facets presented higher activity than Bi(012) for the formate pathway. In addition, the co-modification of sulfur anions and sodium cations improved Bi–Bi metallic bonds, enhanced electron localization of ∗OCHO, and facilitated water activation to form H∗, which enabled the promotion of formate selectivity while suppressing H₂ production. The Bi(110)-S-Na catalyst exhibited one of the highest CO₂-to-formate partial current densities of 2,505 mA·cm⁻² with 83.5% faradaic efficiency. Our work suggests an attractive electrochemical reconstruction strategy to build highly exposed Bi(110) facets with surface modification toward efficient CO₂-to-formate electrosynthesis.