Fast cooling induced grain-boundary-rich copper oxide for electrocatalytic carbon dioxide reduction to ethanol

Electrochemical CO₂ reduction with rationally designed copper-based electrocatalysts is a promising approach to reduce CO₂ emission and produce value-added products. Grain boundaries and micron-strains inside catalysts have been proposed as active catalytic sites, while the controlled formation of these sites has remained highly challenging. In this work, we developed a strategy of creating high-density grain boundaries and micron-strains inside CuO electrocatalysts by fast cooling with liquid nitrogen. Compared to samples with slower cooling rates, the fast cooled CuO showed clear difference in their crystal domain sizes, micro-strain densities, and the chemisorption capacities of CO₂ and CO. This micro-strain-rich CuO electrocatalyst exhibited a high total current density over 300 mA·cm^-2, and an outstanding Faradaic efficiency for C₂ products (with a majority to ethanol) at -1.0 V vs. reversible hydrogen electrode. Our work suggests a facile approach of tuning grain boundaries and micro-strains inside Cu-based electrocatalysts to scale up electrochemical CO₂ reduction for high value-added products.