BiOBr electrocatalytic CO₂ reduction coupled with Ni(OH)₂·0.75H₂O/NF electrocatalytic CH₃OH oxidation for formic acid co-production system

Electrocatalytic CO₂ reduction to formic acid is one of the promising approaches for realizing CO₂ resource utilization. However, the industrial application of this technology still faces challenges, such as low catalyst activity and high energy consumption in the reaction system. To develop efficient catalysts, Br elements were introduced into Bi₂O₃ synthesized via a two-step solvothermal and air roasting process, successfully yielding BiOBr with smaller particle sizes. Within a large current density range of −100 to −500 mA·cm⁻², faraday efficiency of formate (FE_formate) of BiOBr consistently remained around 90%, significantly outperforming the performance of Bi₂O₃. Combined with the characterization results of the catalyst after the reaction, it is demonstrated that Br elements can enhance the CO₂ electroreduction (CO₂RR) performance by modulating the catalyst size. A simple electrodeposition method was used to synthesize a CH₃OH electrooxidation (MOR) catalyst, Ni(OH)₂·0.75H₂O/nickel foam (NF), which achieved a maximum FE_formate of 94.5%. To improve the economic viability of the reaction system, a coupling system of formic acid co-production (CO₂RR//MOR) was constructed, with BiOBr as the cathode and Ni(OH)₂·0.75H₂O/NF as the anode. Compared to the CO₂RR//oxygen evolution reaction (OER) system, the CO₂RR//MOR system reduced energy consumption by 39.3% and increased formic acid production by 45.5%. The results of the techno-economic analysis indicate that, compared to the CO₂RR//OER system, the CO₂RR//MOR system increases profit by 424.7 USD per ton of CO₂ processed, turning the electrolysis system economically from a loss to a profit.