Creating Polycrystalline Cu Catalysts via Capping Agents and Electrochemical Treatment for CO₂ Reduction to C₂H₄

Carbon–carbon coupling is desirable for the electrochemical reduction of carbon dioxide (CO2RR) into high-energy-density C2+ products, but it still remains a challenge owing to product diversity. Here, polycrystalline Cu catalysts were constructed through capping agents and electrochemical treatment. The capping agents assist in the effective synthesis of the sharp-tip flower CuO pre-catalysts with rough surfaces and abundant grain boundaries. After electrochemical treatment, the in situ-generated polycrystalline Cu catalyst exhibits 34% Faradaic efficiency for the C2H4 product at −1.5 V versus reversible hydrogen electrode. With a quasi-in situ total reflection Fourier-transform infrared spectroscopic study, we captured a critical *COOH intermediate on the polycrystalline Cu surfaces, providing direct evidence to support the hypothesis that CO2 initially undergoes the activation process to generate *COOH. Our work offers insights into the rational design of selective Cu catalysts for C2+ products in CO2RR