M–O–C Catalysts: Copper Single Atoms Supported on Oxocarbon Covalent Networks as Electrocatalysts for Glycerol Oxidation to Formic Acid

N-doped carbon single-atom catalysts (M-N-C) have emerged as some of the most efficient electrocatalysts, offering both high activity and selectivity. To date, stabilization of single atoms on conductive carbon has been achieved almost exclusively through coordination with nitrogen atoms. Here, we introduce copper single-atom catalysts (Cu SACs) uniquely coordinated by oxygen within a stable oxocarbon network derived from tetrahydroxyquinone (THQ)-Cu metal-organic frameworks. By thermal condensation with MgCl₂·6H₂O at 600 °C, we achieve an oxygen-rich carbonaceous material (30 wt% O) hosting highly dispersed Cu atoms. Advanced electron microscopic, spectroscopic, and scattering techniques, including high-resolution scanning transmission electron microscopy (HR-STEM), X-ray absorption spectroscopy (XAS), pair distribution functions (PDF), and electron energy loss spectroscopy (EELS), provide definitive experimental evidence of predominant Cu-O coordination, distinguishing these catalysts (M-O-C) from conventional nitrogen-coordinated SACs. The resulting Cu-O-C catalyst exhibits high selectivity (85% Faradaic efficiency) for electrochemical glycerol oxidation into formic acid under alkaline conditions, outperforming traditional Cu-based systems. In comparison with traditional Cu-N-C system, Cu-O-C shows faster reactions kinetic, arising from unique Lewis basicity of oxygen coordination, facilitating electron-proton transfer reactions. This study not only pioneers Cu-O-C SACs but also introduces oxocarbons as promising supports, offering novel pathways for designing highly efficient single-atom electrocatalysts.