Ultrafine bismuth nanoclusters for highly efficient electrochemical CO₂ reduction to formate

Electrochemical CO₂ reduction (ECR) to formate offers a viable avenue for CO₂ neutrality and utilization. However, enhancing the ECR performance and maintaining its activity under diluted CO₂ conditions remains a challenge. This study presents a facile method for the gram-scale production of ultrafine Bi nanoclusters (sub-2 nm) supported on activated carbon (Bi NCs/AC) for efficient ECR to formate. The Bi NCs/AC demonstrates a maximum faradaic efficiency of 98.8 % at −0.8 V vs. RHE in an H-cell with 0.5 M KHCO₃ electrolyte under ambient conditions, coupled with long-term stability over 60 h. In a flow cell equipped with a gas diffusion electrode in 1.0 M KOH electrolyte, it delivers superior CO₂-to-formate performance with current densities over 200 mA cm⁻². Remarkably, this outstanding performance is well maintained even at diluted CO₂ feedstocks (15–30 vol% CO₂ balanced by N₂). When tested with a complex gas mixture to mimic flue gas, the CO₂-to-formate performance remains unaffected by the impurities, except for O₂. Theoretical investigation reveals that the facilitated *OCHO formation process is the preferred pathway for formate production, consistent with in-situ Raman results that confirm the reaction pathway involving *OCHO intermediate. Our work presents a new approach for developing Bi-based catalysts with practical utilization in ECR.