Surface Hydroxyl Network Promoted Hydrogen Transfer Dynamics for Efficient Photocatalytic Acetylene Semi‐Hydrogenation

Abstract Photocatalytic semi‐hydrogenation of acetylene (C 2 H 2 ) to ethylene (C 2 H 4 ) is seriously limited by the inefficient generation and directional transfer of active hydrogen species. Here, we report a proton‐coupled electron transfer (PCET) mechanism for photocatalytic acetylene semi‐hydrogenation by establishing a hydroxyl network over hydroxyl‐modified carbon nitride (C 3 N 4 ‐OH)/Ni(OH) 2 composite. Such a hydroxyl network not only enhances photogenerated charge separation but also establishes a strong hydrogen‐bonding microenvironment for adsorbing interfacial water and facilitating hydrogen transfer dynamics. Femtosecond transient absorption (fs‐TA) spectroscopy, in situ photochemical infrared spectroscopy, kinetic isotope effect (KIE), and active hydrogen (H*)‐trapping reveal that the fast proton transfer via a PCET mechanism, rather than a conventional hydrogen atom transfer (HAT) pathway. Eventually, the C 3 N 4 ‐Ni(OH) 2 achieves an exceptionally high C 2 H 4 production rate of 15.7 mmol g cat −1 h −1 with a C 2 H 4 selectivity of 98.2% under simulated solar irradiation. For purifying a crude C 2 H 4 stream containing 0.5 vol% C 2 H 2 , the C 2 H 2 conversion remains ∼98% over a long‐term continuous‐flow operation. This work elucidates the pivotal role of surface hydroxyl networks in governing hydrogen kinetics and paves a new avenue for the design of high‐performance photocatalysts.