Modification Of Graphitic Carbon Nitride For Electrochemical Oxygen Reduction To Produce Hydrogen Peroxid

As a green oxidant,hydrogen peroxide（H₂O₂）is one of the 100 most indispensable chemicals on the earth,and its annual demand is very large,exceeding 4 million tons.By 2024,this demand will reach 6 million tons per year,with a market value of 6.4billion dollors.However,more than 95%of hydrogen peroxide comes from anthraquinone process,but this method has some disadvantages such as complex reaction,serious energy consumption and serious pollution.This key energy-consuming industry is undoubtedly contrary to China’s goal of"carbon neutrality in peak carbon dioxide emissions".Therefore,it is necessary for us to consider the preparation of hydrogen peroxide by electrochemical reduction of oxygen（2e^-ORR）.It is more environmentally friendly and safe,and can prepare hydrogen peroxide under relatively mild conditions,so as to reduce the impact of hydrogen peroxide production on the environment,which is more in line with the current industrial green development needs.At present,it has been proved that many materials can be used in 2e^-ORR catalysts,from precious metals and their alloys to transition metal oxides and nonmetallic materials.Among many materials,graphite carbon nitride（g-C₃N₄）has attracted people’s attention as a nonmetallic catalyst because of its rich electronic structure and good physical and chemical stability.Recent studies show that g-C₃N₄ can be used as an ideal platform to adjust the electronic structure and geometric structure of catalysts^[1].Based on the structural advantages of g-C₃N₄,the catalytic activity of g-C₃N₄/CQDs composite was improved from two aspects:the reasonable design of nano-carbon materials,that is,the screening of graphite carbon nitride precursors,the adjustment of functional groups on the surface of g-C₃N₄,the regulation of its 2eorr performance and the stripping of layered g-C₃N₄ and carbon dots（CQDs）self-doping by ultrasonic-assisted method,which has certain practical application value.The research contents of this paper are as follows:1.Regulation of surface functional groups of g-C₃N₄ on its 2e^-ORR properties.Aiming at the problems of poor conductivity and low selectivity of metal-free carbon-based materials at present,the precursor screening strategy of g-C₃N₄ was adopted to control the concentration of nitrogen species groups on the surface of g-C₃N₄to achieve high selectivity in preparing hydrogen peroxide.Among them,the selectivity of g-C₃N₄ hydrogen peroxide prepared with urea as precursor is as high as about 90%.We found that the high concentration of graphite nitrogen in alkaline condition is helpful to the adsorption of O₂ in the initial stage of the reaction and the retention of O-O bond in*OOH during the reaction,which has a significant effect on the selectivity of 2e^-ORR.2.Ultrasonic-assisted preparation of g-C₃N₄/CQDs composites preparation of hydrogen peroxide by efficient oxygen reduction.Aiming at the common problems of layered materials at present,the method of ultrasonic-assisted stripping of layered g-C₃N₄ was developed,and the strategy of carbon point self-doping layers of g-C₃N₄ was realized by ultrasonic wave,thus hydrogen peroxide was prepared with high selectivity and high yield.The effects of ultrasonic duration on the physical properties and oxygen reduction reaction（ORR）of g-C₃N₄materials were discussed.Electrochemical analysis showed that the selectivity of g-C₃N₄to hydrogen peroxide was as high as 95%under alkaline conditions.It is precisely because of the recombination of CQDs（Carbon Quantum Dots）,the introduction of vacancy defects and the stripping of multi-layer materials to less-layer materials that the conductivity of materials is enhanced,the active surface area is increased and the catalytic performance is improved.The research results in this paper show that the reasonable design and adjustment of nonmetallic nano-carbon materials can effectively change the catalytic activity of the catalyst for 2e^-ORR.The relevant reaction process and the research results of electrode materials provide a theoretical basis for the practical application of electrochemical synthesis of H₂O₂.