Copper-stabilized bismuth subcarbonate electrocatalysts for durable large-scale formate production at kilowatt power

Electrochemical CO₂ reduction (CO₂RR) to formate offers a sustainable route for decarbonization, yet achieving both high catalytic selectivity and stability remains challenging. Herein, we achieve a high formate Faradaic efficiency of 92.5% and full-cell energy efficiency of 53.8% at 30 A in a 100 cm² alkaline membrane electrode assembly (MEA) electrolyzer based on the designed bismuth subcarbonate stabilized with copper (Cu@BOC) catalyst. The electrolyzer demonstrates durable electrolysis at 30 A for 130 h, producing a formate yield of 98.5 mol in 24.5 L of electrolyte (4.02 M). In situ electrochemical spectroscopy measurements reveal the critical role of Cu dopants in stabilizing the catalyst structure from self-reduction, enhancing *OCHO adsorption, and suppressing the competitive hydrogen evolution. A scale-up coupled electrolysis system achieves a molar-scale formate production rate of 10.5 mol h^-1 at 2.1 kW and 100 A with a 5 × 100 cm² MEA electrolyzer stack. This rationally designed coupling electrosynthesis system with efficient formate production performance should significantly accelerate practical industrial applications of CO₂RR to formate.