Heteroleptic Dicopper Molecular Design Unlocks Distinct Dual Synergies in Electrocatalytic Hydrodimerization of Dilute Acetylene to 1,3‐Butadiene

ABSTRACT Electrocatalytic hydrodimerization of acetylene to 1,3‐butadiene is an attractive sustainable route, yet reconciling the disparate kinetic demands of acetylene dimerization and hydrogenation remains challenging, especially in catholyte‐free membrane electrode assembly (MEA) systems with dilute acetylene feeds. Herein, we report a heteroleptic dicopper molecular catalyst featuring piperonylate and acetate ligands that effectively addresses this incompatibility—a distinctive advantage over homoleptic catalysts. Mechanistic studies reveal that the heteroleptic design provides distinct dual synergies: (i) heteroleptic coordination minimizes steric hindrance and optimizes the Cu d ‐band center of dicopper sites, promoting efficient acetylene activation and dimerization; (ii) heteroleptic‐induced localized electric fields reorganize interfacial water structure and enrich free water molecules, critically enhancing hydrogen availability for hydrogenation. The heteroleptic catalyst substantially surpasses homoleptic analogues across a broad range of acetylene concentrations (15%–100%), delivering 91% Faradaic efficiency toward 1,3‐butadiene at just 15% acetylene in a flow cell. In a MEA setup, the catalyst continuously operates at −500 mA for 31 h, converting 15% acetylene to 1,3‐butadiene and accumulating 224 mmol of product despite restricted hydrogen availability. This work demonstrates heteroleptic molecular design as a powerful and versatile strategy for selectively controlling competing pathways in complex multi‐carbon electrosynthesis.