The Preparation And Study Of Defect-Rich Carbon Nanofibers For Electrochemical Water Oxidation To Hydrogen Peroxide

The electrocatalytic two-electron water oxidation reaction（2e^--WOR）offers a promising pathway to directly produce high-value hydrogen peroxide by using water as the reactant.So far,the 2e^--WOR electrocatalyst system mainly relies on metal oxides.These electrocatalysts generally show relatively high selectivity,while the current densities are very low.Recently,carbon-based materials have attracted tremendous attentions because of their excellent electrical conductivity.However,the present H₂O₂ Faradaic efficiency（FE）over carbon-based materials is still far from satisfactory.Thus,the development of carbon-based electrocatalysts with attractive efficiency and selectivity for 2e^--WOR is a challenging but promising subject.In this work,intrinsic carbon defect-rich carbon nanofibers（CNFs/NF-x）were prepared and used for 2e^--WOR,which results showed that it significantly enhances the Faraday efficiency and current density of H₂O₂.Meanwhile,the role of carbon defects in promoting 2e^--WOR was studied.The main contents are as follows:Carbon nanofibers supported on nickel foam（CNFs/NF）were prepared by the chemical vapor deposition method under different temperatures where the Ni substrate itself catalyzes the growth of CNFs.Raman spectra and X-ray photoelectron spectroscopy（XPS）indicate that the samples contain rich intrinsic carbon defects.The electrocatalytic study showed that the concentration of intrinsic carbon defects in CNF samples has a significant correlation with their 2e^--WOR performance.A H₂O₂ FE of41.2%was achieved at 2.9 V vs.RHE over CNFs/NF-600,and corresponding H₂O₂current density reached 72.6 m A cm^-2.The H₂O₂ FE further increased to 53.8%after PTFE modification,and 48.1%H₂O₂ selectivity was still achieved after 8 h stability test,demonstrating good stability of CNFs/NF@PTFE-600.In addition,this method of controlling the 2e^--WOR selectivity by intrinsic carbon defect can be effectively extended to cobalt foam substrate.The adsorption strength of intermediates on the surface of CNFs/NF-x were probed by the methanol competitive oxidation experiments and in-situ Raman spectra,which results indicated the different types of intrinsic carbon defects contained in CNFs/NF-x.Moreover,the types of defects were studied by XPS and near-edge X-ray absorption fine structure,and the results show that CNFs/NF-600 with optimum performance contains rich ring defects.Density functional theory studies revealed that the adsorption free energy of OH*intermediates over ring defects is closer to the apex of the volcanic curve,thus enhancing the selectivity of H₂O₂.In summary,the efficient 2e^--WOR was achieved over intrinsic carbon defect-rich carbon nanofibers and the relation between ring defects and H₂O₂ selectivity was established,which offers a helpful attempt to explore efficient 2e^--WOR carbon-based electrocatalysts.