Molecular Cobalt Catalysts for Highly Selective Electrocatalytic Acetylene Semi-Hydrogenation

Abstract Electrocatalytic acetylene semi-hydrogenation (EASH) offers a facile pathway for ethylene production. However, competing side reactions, particularly hydrogen evolution, over-hydrogenation, and C–C coupling, severely compromise its selectivity and industrial viability. Here, we present a cobalt-centered molecular catalyst platform, which can significantly suppress these parasitic side reactions via simply modulating the Co phthalocyanines (CoPcs) catalyst electronically. In this class of molecular catalysts, CoPc-based structures exhibit markedly enhanced water dissociation kinetics and elevated C–C coupling energy barriers compared to conventional CuPc-based structures, thereby effectively suppressing undesired C–C coupling. Molecular regulation of the Co center in CoPc further optimizes its active hydrogen adsorption and utilization, mitigating both hydrogen evolution and over-hydrogenation. The rationally engineered CoPc molecules supported on nitrogen-chelated carbon nanotubes (CoPc/NCNT) thus exhibit outstanding EASH performance under both high current densities and ethylene-rich conditions. At an industrially relevant current density of 500 mA cm⁻² under a pure C₂H₄ feed, the CoPc/NCNT achieves 86.7% Faradaic efficiency for ethylene with negligible ethane (<0.01%) and no C₄ byproducts, which delivers a record turnover frequency of 9.7 × 10³ min⁻¹, surpassing other catalysts reported to date. Moreover, under simulated industrial crude ethylene conditions, this catalyst maintains 99.7% acetylene conversion and 99.2% ethylene selectivity even during 24-hour continuous operation, demonstrating its exceptional stability and practical application potential for scalable ethylene purification. This study not only establishes the dual advantage of cobalt in suppressing C–C coupling while enabling selective hydrogenation but also provides a well-defined molecular strategy for tailoring molecular catalysts to advance electrocatalytic transformations.