The electrochemical CO₂ reduction reaction (CO₂RR) to formate offers a promising pathway to mitigate the energy crisis and realize carbon neutrality. Bismuth (Bi), as a metal catalyst for the CO₂RR, is considered to have great potential in producing formate, yet hindered in low current density and selectivity. Herein, we constructed an oxide-derived copper foam substrate (OD-Cu) to improve the electrocatalytic properties of Bi dendrites loaded on its surface. Bi electrodeposited on the OD-Cu (Bi/OD-Cu) grows as pinecone-like dendrites, exhibiting a high formate faradaic efficiency (FE_formate) of 97.2% and a formate partial current density of ~24 mA·cm⁻² at −0.97 V vs. RHE (reversible hydrogen electrode) in an H-cell. Notably, the Bi/OD-Cu electrode demonstrates an FE_formate of 95.8% at −0.97 V vs. RHE and a total current density close to 90 mA·cm⁻² at −1.17 V vs. RHE in a neutral flow cell. The experimental studies reveal that the remarkable CO₂RR performance of the Bi/OD-Cu results from the electron transfer from Cu to Bi, which optimizes adsorption of the CO₂^•− and boosts reaction kinetics. This study emphasizes the crucial role of substrate engineering strategies in enhancing catalytic activity and shows the possibility for a porous metal electrode in advancing the industrialization of formate production.

Effective electrochemical reduction of carbon dioxide to formate under mild conditions helps mitigate the energy crisis but requires the use of high-performance catalysts. The addition of a third metal to the binary metal catalyst may further promote the electrochemical reduction of carbon dioxide to formate. Herein, we provided a co-electrodeposition method to grow CuSnBi catalysts on pretreated copper foam and discussed the effects of both pH value and molar ratio of metal ions (Cu²⁺, Sn²⁺, and Bi³⁺) in the electrodeposition solution on the electrocatalytic performance of CO₂ to HCOO⁻. When the pH value of the electrodeposition solution was 8.5 and the molar ratio of Cu²⁺, Sn²⁺, and Bi³⁺ was 1:1:1, the electrode showed the highest FE_HCOO⁻ of 91.79% and the formate partial current density of 36.6 mA·cm⁻² at −1.12 V_RHE. Furthermore, the electrode kept stable for 20 h at −1.12 V_RHE, and FE_HCOO⁻ was always beyond 85% during the electrolysis process, which is excellent compared to the previously reported ternary metal catalytic electrodes. This work highlights the vital impact of changes (pH value and molar ratio of metal ions) in electrodeposition liquid on catalytic electrodes and their catalytic performance, and refreshing the electrolyte is essential to maintain the activity and selectivity during the electrochemical reduction of CO₂ to HCOO⁻.

The efficient electrochemical reduction of carbon dioxide to formate under mild conditions is a promising approach to mitigate the energy crisis, but requires the use of high-performance catalysts. The selectivity and activity of catalysts can be enhanced through multi-metal doping, further advancing the electrochemical reduction of CO₂ to formate. This study demonstrates a co-electrodeposition strategy for synthesizing SnBi electrocatalysts on pretreated copper foam substrates, systematically evaluating how the Sn²⁺/Bi³⁺ molar ratio in the electrodeposition solution and the applied current density affect the catalytic performance for CO₂-to-formate conversion. Optimal performance was achieved with a molar ratio of Sn²⁺ to Bi³⁺ of 1:0.5 and a deposition current density of 3 mA cm⁻², resulting in a formate Faradaic efficiency (FE_formate) of 97.80% at −1.12 V (vs. RHE) and a formate current density of 26.9 mA·cm⁻². Furthermore, the Sn₁Bi_0.50-3 mA·cm⁻² electrode demonstrated stable operation at the specified potential for 9 h, maintaining a FE_formate above 90%. Compared to previously reported metal catalysts, the SnBi catalytic electrode exhibits superior performance for the electrochemical reduction of CO₂ to HCOOH. The study highlights the significant impact of the metal ion molar ratio and deposition current density in the electrodeposition process on the characteristics and catalytic performance of the electrode.