Plasmonic Hot‐Carrier Redox Enables Proton‐Coupled Electron Transfer at C─H Bonds

Abstract Proton‐coupled electron transfer (PCET) enables the activation of strong X─H bonds (X = C, N, O) under mild conditions, yet mechanistic interrogation remains challenging due to limited control over electron and proton energetics. Here, we demonstrate that plasmon‐driven photocatalysis provides a powerful platform to disentangle these contributions. Using gold nanoparticles supported on an engineered energy‐filter substrate as photoelectrodes, we achieve oxidative C─H bond activation in 1‐benzyl‐1,4‐dihydronicotinamide via multi‐site PCET under visible‐light excitation. Photocurrent kinetics and energetics zone analysis reveal an electron‐then‐proton transfer (ET–PT) pathway that requires pre‐association of the base. The average plasmonic oxidation potential is estimated at ∼0.64 V versus Fc⁺/Fc, corresponding to hot‐hole energies of ∼0.52 eV. These findings establish plasmonic materials not only as versatile light absorbers for photoredox catalysis but also as mechanistic probes for resolving fundamental PCET pathways.