• • TGB-CuO achieves a Faradaic efficiency of 80.15% for C2+ products, with over 50% ethylene selectivity at 300 mA cm−2, sustained for 30 h, demonstrating industrial relevance for high-rate CO2 conversion.
• • The Turing-type grain boundary architecture is formed at ~10 nm scale via balanced diffusion-reaction dynamics during pyrolysis, enabling high-density defects that are otherwise difficult to achieve.
• • Specific grain boundary types (Cu(100)/(100), Cu(100)/(111), Cu(111)/(111)) are identified as active sites that lower the free energy barriers for the rate-determining steps (*CO2− → *COOH and C–C coupling), enhancing reaction kinetics.
• • The catalyst retains its Turing-type grain boundary features after electroreduction (TGB-Cu), indicating structural stability under operating conditions, crucial for long-term durability.