Insights into the Role of Bismuth Oxidation State in Bi‐Based Nanocatalysts for High‐Efficiency CO2 Electroreduction to Formate

Electrocatalytic reduction of CO2 to formate (HCOO−) using Bi‐based nanocatalysts shows great promise in “carbon‐neutrality” and green chemical synthesis. However, the functional active species, metallic Bi or Bi‐O structure, responsible for CO2‐to‐HCOO− is still in debate. In this study, we found that nanodendritic Bi‐metal electrocatalyst, synthesized via one‐step electrodeposition method, exhibited ~100% Faradic efficiency to HCOO− at ‐0.98 VRHE, which was much superior to that from Bi‐plasma mainly composed of Bi2O3 (Faradic efficiency, 76.7%). The in‐situ Raman spectra and density functional theory (DFT) calculations collectively confirmed that zero‐valent Bi metal, rather than Bi‐O structure, is crucial for HCOO− production from CO2 electroreduction. In addition, the Bi‐metal nanocatalysts exhibited high stability maintaining >95% performance over 94‐hour reaction and the photovoltaic‐electrocatalysis system achieved about 1% solar‐to‐formate conversion efficiency. This work elucidates the functional Bi‐containing species in CO2 electroreduction, providing guidance onto effective Bi‐based electrocatalysts design for formate production.