Molecular cobalt catalysts for electrocatalytic acetylene semi-hydrogenation

Electrocatalytic acetylene semi-hydrogenation is an attractive route for ethylene production, but competing side reactions like hydrogen evolution, over-hydrogenation, and C–C coupling severely compromise its industrial viability. Here, we present a carbon-nanotube-supported metal phthalocyanine platform, MPc/XCNT (M = Cu, Co, Ni, Fe; X = O, N, S), to investigate the roles of metal centers and local coordination environments. Among these catalysts, CoPc-based structures exhibit markedly enhanced water dissociation kinetics and elevated C–C coupling energy barriers compared to conventional CuPc-based catalysts, thereby effectively suppressing undesired C4 by-products. Furthermore, molecular regulation of the Co center optimizes active hydrogen adsorption and utilization, mitigating both hydrogen evolution and over-hydrogenation. As a result, the optimized CoPc/NCNT catalyst delivers competitive performance under both high current densities and ethylene-rich conditions. At an industrially relevant −500 mA cm−2 under a pure ethylene feed, it achieves 86.7% Faradaic efficiency with a turnover frequency of 7019 min−1. Under simulated industrial crude conditions, it maintains 99.7% conversion and 99.5% selectivity during 110-hour continuous operation. This work provides a well-defined molecular strategy for advancing selective electrocatalytic transformations. Selective electrocatalytic acetylene-to-ethylene conversion is limited by competing side reactions over molecular catalysts. Here, the authors report a cobalt phthalocyanine catalyst that achieves 99.99% ethylene selectivity and a turnover frequency of 7019 min-1 at -500 mA cm-2.