Construction Of Functional Groups On The Surface Of Carbon-based Electrocatalysts To Enhance The Activity Of Two-electron Oxygen Reduction Reaction

As a clean and green oxidant,hydrogen peroxide has been widely used in domestic life,medical field and industrial production.Therefore,it is necessary to increase the output of H₂O₂to meet the needs of various scenarios.The main production technology of H₂O₂ is anthraquinone process,which requires plentiful toxic organic solvents.The electro-catalytic oxygen reduction method can produce H₂O₂ continuously and efficiently,which avoids complex production processes.This method undergoes mild reaction conditions and more convenient.Carbon-based catalysts have advantage of abundant raw materials,low prices,and easy preparation,which have become a research hotspot for researchers in recent years.In this paper,carbon black with high specific surface area,graphite-phase carbon nitride and boron-rich B₄C are used as the initial raw materials.Through oxidation treatments,metal thermal reduction or immersion methods for carbon coating,high-efficiency two-electron electrocatalytic oxygen reduction catalyst can be prepared.Then,a series of structure characterization and electrochemical performance test are carried out to explore the relationship between the catalyst structure and performance.The specific research contents are as follows:Firstly,through CO₂ oxidation treatment,oxygen-containing functional groups are introduced on the surface of the carbon black.We explore the differences of oxygen-containing functional groups and oxygen content introduced at different oxidation temperature and time.Experimental results have proved that through CO₂ oxidation treatment,a large number of defects are introduced on the surface of carbon black.The pore volume and average pore diameter of the material are slightly increased,which leads to the improvement of the catalytic performance of the material.Among the oxygen-containing functional groups introduced on the surface of the material,the C=O bond is the active oxygen functional group in the 2-electron ORR electrocatalyst.The catalyst CB-CO₂-500-2 prepared by calcination at 500°C for 2h has the best catalytic performance.Specifically,the initial potential and half-wave potential are 0.82V（vs.RHE）and 0.75 V（vs.RHE）,respectively.The H₂O₂ selectivity is 80.63%,and the catalyst has good electrochemical stability and high H₂O₂ production.Secondly,using melamine as a raw material,graphite phase carbon nitride is prepared by thermal polymerization.Then,the prepared g-C₃N₄ is thermally reduced using magnesium metal powder to prepare a new type of nitrogen-doped porous carbon material.Through CO₂oxidation treatment,oxygen element is introduced onto the surface of the catalyst.The influence of the introduction of oxygen on the catalytic performance of the material is explored.The experimental results show that while the magnesium powder acts as a reducing agent,it also acts as a pore-forming agent.After thermal reduction,a large number of defects are introduced on the surface of the material and BET specific surface area is greatly increased.A larger specific surface area is conducive to the distribution of catalytic active sites,thereby improving the catalytic performance of the material.Further oxidation treatment introduces oxygen-containing functional groups on the surface of the material,which further affects the catalytic activity of the catalyst.The study finds that among the prepared materials,NC-O-500has excellent catalytic activity,with the initial potential and half-wave potential of 0.85 V（vs.RHE）and 0.76 V（vs.RHE）,respectively,and the H₂O₂ selectivity is 79.40%.The 10 hours’electrochemical stability test shows that it has good stability,and the highest H₂O₂ yield is1781.25 mmol g cat^-1 h^-1.Finally,using boron-rich B₄C as the raw material and glucose as carbon source,a layer of carbon is coated with B₄C by impregnation and carbonization.The subsequent oxidation treatment process introduces oxygen-containing functional groups onto the carbon coating layer of the material,further improving the electrocatalytic performance of the material to prepare H₂O₂.The prepared catalyst B₄C@C-CO₂ has excellent 2-electron ORR performance and high H₂O₂ yield.Studies have shown that the introduced oxygen-containing functional group C=O bond and BCO₂ configuration are the active groups for the preparation of H₂O₂ by 2-electron oxygen reduction reaction.