Grain-boundary engineering of bismuth catalyst enables industrial-current-density CO₂ electroreduction to formate via stabilizing *OCHO intermediate

Electrochemical CO₂ reduction reaction (CO₂RR) to formate offers a promising carbon-neutral route. However, industrial-current-density operation (>200 mA cm⁻²) is hindered by insufficient catalytic activity and selectivity. Herein, a grain-boundary-rich bismuth catalyst (wrinkled Bi) was constructed via rapid in situ electrochemical reconstruction of a surface-wrinkled Bi₂₄O₃₁Cl₁₀ precursor, demonstrating exceptional CO₂-to-formate electroreduction performance at industrial current densities. Notably, at a potential of −1.0 V versus the reversible hydrogen electrode (vs. RHE), wrinkled Bi achieved a Faradaic efficiency of up to 94.0 % for formate production with a current density of 22.8 mA cm⁻² in an H-type cell, and it also exhibited excellent durability with stable operation for 105 h. Furthermore, the Faradaic efficiency remained above 96.4 % in the current density range of 100–800 mA cm⁻², reaching a maximum value of 99.1 % at 600 mA cm⁻² in a flow cell. In situ infrared spectroscopy and density functional theory (DFT) calculations revealed that the grain boundaries in wrinkled Bi can stabilize *OCHO intermediate and restrain H* desorption, facilitating formate generation and suppressing hydrogen evolution. The grain boundary engineering provides new insights into the design of efficient catalysts for industrial-current-density electrochemical CO₂ reduction to formate.