Descriptor for electro-oxidation of glycerol with high-efficiency bifunctional Cu-N_x single atom catalyst and coupled with hydrogen evolution/carbon dioxide reduction

Electrochemical glycerol oxidation reaction (GOR) presents a promising approach for converting excess glycerol (GLY) into high-value-added products. However, the complex mechanism and the challenge of achieving selectivity for diverse products make GOR difficult to address in both experimental and theoretical studies. In this work, three nitrogen-doped graphene-supported copper single-atom catalysts (CuN_x@Gra SACs, x = 2-4) were selected as the model system due to their simple structure, excellent conductivity and high structural stability. Density functional theory (DFT) calculations were employed to gain deeper insight into the catalytic mechanism. The DFT results revealed that both CuN₂@Gra and CuN₃@Gra follow the same optimal pathway, leading to the formation of formic acid as a key product. The GOR activity and selectivity of CuN_x@Gra catalysts follow the trend CuN₃@Gra > CuN₂@Gra > CuN₄@Gra. Subsequent microkinetic analysis, based co on the DFT-derived energetics, confirmed this predicted activity sequence. The GOR activity determined by the limiting potential (U_L) is correlate well with changes in the adsorption free energy (ΔG_GLY*), the d-band centers of axial d_z² orbitals (ε_dz²) and integrated crystal orbital Hamilton population (ICOHP). Notably, the simple descriptor ΔG_GLY* exhibits a good linear correlation with the free energies of other adsorbates, clarifying the conversion relationships between reaction intermediates and simplifying the understanding of reaction complexity. Moreover, computational results indicate that CuN₂@Gra and CuN₃@Gra systems can serve as both anode catalysts (for GOR) and cathode catalysts (CO₂ reduction for CuN₂@Gra and H₂ evolution for CuN₃@Gra). This study offers insights for designing efficient electrocatalysts, enhancing GLY utilization.