Grain Boundary-Engineered Cu ₂ O for Selective CO ₂ -to-Acetate Conversion

Direct electrocatalytic CO2 reduction (eCO2RR) to acetate in membrane electrode assembly (MEA) electrolyzers offers a promising pathway for sustainable chemical production. However, achieving selective C–C coupling toward acetate remains highly challenging because of competing multicarbon (C2+) formation pathways. Herein, we propose a grain boundary engineering strategy to regulate acetate selectivity. Unlike conventional Cu-based catalysts that primarily produce ethylene and ethanol, introducing high-density grain boundaries fundamentally reshapes the local microenvironment of catalyst. This structural modification stabilizes absorbed CO intermediates and alters the local coordination of active Cu sites, thus suppressing competing ethylene and ethanol pathways. As a result, this structural control achieves a remarkable acetate selectivity of 38% and maintains a stable operation over 47 h at 100 mA cm–2 in a 5 cm2 MEA electrolyzer, representing the highest acetate selectivity under neutral conditions. Our findings establish a direct structure–selectivity correlation between grain boundary density and acetate production, highlighting grain boundary engineering as a powerful and generalizable strategy for designing defect-driven catalysts in practical CO2 electrolysis.