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

Abstract Electrocatalytic reduction of CO 2 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 CO 2 reduction 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 V RHE , which was much superior to that from Bi‐plasma mainly composed of Bi 2 O 3 (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 CO 2 electroreduction. In addition, the Bi‐metal nanocatalysts exhibited high stability maintaining >95% performance over 94 h reaction and the integration with photovoltaic‐electrocatalysis system achieved about 1% solar to formate conversion efficiency. This work elucidates the functional Bi‐containing species in CO 2 electroreduction, providing guidance onto effective Bi‐based electrocatalysts design for formate production.