Electrochemical Alkyne Semi‐Hydrogenation via Proton‐Coupled Electron Transfer on Cu(111) Surface

Abstract Electrocatalytic alkyne semi‐hydrogenation (EASH) powered by renewable electricity using water as a hydrogen donor provides a sustainable alternative to conventional thermocatalysis. However, the current EASH systems predominantly follow hydrogen atom transfer (HAT) pathways, which are prone to over‐hydrogenation and at the same time compete with the hydrogen evolution reaction. In this work, we report a proton‐coupled electron transfer (PCET) mechanism enabled on Cu(111) surface for highly efficient and selective EASH. Well‐defined two‐dimensional Cu nanosheets with exposed (111) facets achieve > 98% selectivity for electrochemical semi‐hydrogenation of 4‐aminophenylacetylene to 4‐vinylphenylamine in a membrane electrode assembly reactor. The Cu nanosheets can also efficiently remove 1%–8% alkyne impurities in alkene and exhibit broad substrate scope, stereoselectivity, as well as operational stability. In situ Raman spectroscopy measurements reveal that, during the PCET‐mediated EASH, the covalent adsorption of alkynes and their conversion to weakly bound planar intermediates facilitate the EASH process and suppress over‐hydrogenation. Interfacial K + ‐structured and linearly hydrogen‐bonded water species further enhance EASH selectivity via proton supply and steric modulation. Radical scavenging and kinetic isotope effect studies, along with theoretical calculations, corroborate a PCET‐dominated mechanism on Cu(111) surface. This work establishes a PCET‐driven paradigm for selective hydrogenation beyond the conventional HAT pathways.