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

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.