Bismuth nanoparticles supported on carbon nanotubes for highly efficient production of formate for CO2 electroreduction

The electroreduction of CO₂ into formic acid (HCOOH) holds economic value and industrialization potential. Despite that Bi-based materials are effective for producing formic acid, challenges remain due to the insufficient understanding the actual active sites and the lack of facile synthesis of simple materials. We synthesized four bismuth-based catalysts using hydrothermal method (with water as the solvent), which exhibit high selectivity for the reduction of CO₂ to formate. Through comprehensive physical and electrochemical characterizations, we demonstrated that these Bi-based materials underwent reduction and maintained their metallic Bi state at the potentials where CO₂ electroreduction took place. Bulk-Bi displayed the Faradaic efficiency of HCOO⁻ higher than 94.3% from −0.90 V to −1.15 V. Moreover, the Faradaic efficiency of HCOO⁻ remained above 98.1% over 10 h electrolysis at −1.05 V. This finding suggests that metallic Bi serves as the primary active site for the electroreduction of CO₂ to formate. Leveraging this insight, we effectively enhanced the atomic utilization of Bi metal by directly synthesizing metallic Bi nanoparticles. Our results further indicate that these nanoscale Bi particles maintained a high Faradaic efficiency for HCOO⁻ production.