Selective CO₂ Reduction to Ethylene Mediated by Adaptive Small-molecule Engineering of Copper-based Electrocatalysts

Electrochemical CO₂ reduction reaction (CO₂ RR) over Cu catalysts exhibits enormous potential for efficiently converting CO₂ to ethylene (C₂ H₄ ). However, achieving high C₂ H₄ selectivity remains a considerable challenge due to the propensity of Cu catalysts to undergo structural reconstruction during CO₂ RR. Herein, we report an in situ molecule modification strategy that involves tannic acid (TA) molecules adaptive regulating the reconstruction of a Cu-based material to a pathway that facilitates CO₂ reduction to C₂ H₄ products. An excellent Faraday efficiency (FE) of 63.6 % on C₂ H₄ with a current density of 497.2 mA cm^-2 in flow cell was achieved, about 6.5 times higher than the pristine Cu catalyst which mainly produce CH₄ . The in situ X-ray absorption spectroscopy and Raman studies reveal that the hydroxyl group in TA stabilizes Cu^δ+ during the CO₂ RR. Furthermore, theoretical calculations demonstrate that the Cu^δ+ /Cu⁰ interfaces lower the activation energy barrier for *CO dimerization, and hydroxyl species stabilize the *COH intermediate via hydrogen bonding, thereby promoting C₂ H₄ production. Such molecule engineering modulated electronic structure provides a promising strategy to achieve highly selective CO₂ reduction to value-added chemicals.