Interfacial Electron-Proton Dual Modulation of Fe Single-Atom Catalyst by α-MoC for O2 Activation and Lignin Depolymerization.

Efficient O2 activation under mild conditions is central to oxidative biomass valorization, yet single-atom catalysts often suffer from sluggish proton-coupled oxygen intermediate conversion, particularly because of overly strong *OH adsorption. Inspired by the cooperative electron and proton management in cytochrome c oxidase, we report an α-MoC/Fe-N4 catalyst in which α-MoC nanoparticles are interfaced with Fe-N4 single-atom sites on a nitrogen-doped carbon scaffold. The α-MoC component plays a dual role: it withdraws electron density from Fe sites to weaken oxygen-intermediate adsorption and promotes water dissociation to provide local protons for *OH-to-H2O conversion. As a result, α-MoC/Fe-N4 exhibits a 2.8-fold higher Vmax for O2 activation than Fe-N4 and proceeds through a nearly four-electron oxygen reduction pathway with negligible reactive oxygen species (ROS) generation. This interfacial strategy is generalizable to various M-N-C single-atom catalysts, including Mn, Co, Ni, Cu, Sn, Ir, and Pt. Enabled by efficient O2 activation, α-MoC/Fe-N4 depolymerizes native birch lignin under mild alkaline conditions, substantially decreasing its molecular weight and cleaving β-O-4, β-β, and β-5 linkages. This work establishes an electron-proton dual-modulation strategy for constructing high-performance single-atom catalysts for biomass conversion.