Revealing the Valence‐Dependent CO 2 RR Selectivity Mechanism on Molecularly Coordinated Cu 2+ Site Through Second‐Shell Regulation

ABSTRACT Carbon dioxide electroreduction reaction (CO 2 RR) into high‐value C 2 products provides a promising strategy to realize resourceful CO 2 utilization. Rational construction of catalytic sites to unravel their structure‐performance correlation is of great significance for designing high‐performance CO 2 RR catalysts. Cu 2+ centers serve as versatile active sites for CO 2 RR, capable of catalyzing C 2 H 4 and C 2 H 5 OH formation, while the mechanistic origin of this selectivity remains highly ambiguous and inconsistent. Herein, Cu‐based molecular catalysts with different chemical valence of Cu sites through second‐shell coordination regulation are constructed and show a discrepant intramolecular electron redispersion. The low‐valence Cu 2+ sites (Cu 1 ‐BIM, BIM: benzimidazole) deliver an enhanced C 2 ‐product Faradaic efficiency (FE) of up to 80.5% alongside excellent operational stability. A linear scaling relationship that low‐valence Cu 2+ sites are accelerated to C 2 H 4 generation and high‐valence Cu 2+ sites (Cu 1 ‐BTA, BTA: benzotriazole) are beneficial for C 2 H 5 OH formation are established. Mechanism explorations reveal that high‐valence Cu 2+ sites can reduce the energy barrier for *CO hydrogenation, C‐C dimerization, and facilitate *CHCOH deoxygenation through preferentially stabilizing the C─O bond compared to low‐valence Cu 2+ sites. Interestingly, the pulsed‐electrolysis strategy acting as a “catalytic on‐off” can switch the reaction pathway from ethylene‐preferred to ethanol‐oriented by dominating the evolution behavior of Cu 2+ valence.