<p>Constructing abundant grain boundary defects is a promising strategy for developing high-efficiency catalysts. However, achieving dense grain boundary defects in CuO and Cu at the nanoscale remains challenging. Inspired by Turing patterns in nature, a Turing-type CuO catalyst (TGB-CuO) with abundant grain boundaries at ∼10 nm nanoscale was prepared by annealing a dodecyl sulfate-intercalated basic copper carbonate. The balanced diffusion-reaction dynamics during pyrolysis drove the spontaneous formation of Turing-type grain boundary architectures in TGB-CuO. The resulting TGB-CuO electrode exhibited outstanding performance in electrochemical CO₂ reduction (ECO₂RR), delivering a Faradaic efficiency of 80.15% toward multi-carbon (C₂₊) products and maintaining over 50% ethylene selectivity at 300 mA cm⁻² for 30 h of continuous operation. Activity investigations indicated that the metallic Cu retaining Turing-type grain boundary features (TGB-Cu) formed during electroreduction was responsible for the enhanced ECO₂RR performance. The Cu(100)/(100), Cu(100)/(111), and Cu(111)/(111) grain boundaries promoted CO₂ activation and *CO adsorption, while lowering the free energy barriers for the rate-determining *CO₂⁻ → *COOH step and C–C coupling step. This bioinspired reaction-diffusion strategy offers a new paradigm for creating high-density grain boundary defects, offering a general route toward efficient catalyst design.</p>