Preparation Of Graphitic Carbon Nitride And Its Photo/Electrocatalysis And Electrochemical Lithium Storage Performances

As an n-type non-metal two-dimensional layered semiconductor material,g-C₃N₄ has the advantages of easy preparation,low cost,and low toxicity.Because g-C₃N₄ has a narrow band gap,it has been successfully applied to photocatalysis fields such as carbon dioxide reduction and photocatalytic water splitting for hydrogen evolution.However,the original g-C₃N₄photogenerated electron-hole pair is easy to recombine and has a small specific surface area,which limits its application in photocatalytic moisture analysis of hydrogen.In addition,g-C₃N₄ is nitrogen-rich and is considered to be a special nitrogen-doped carbon material,which has broad application prospects for electrochemical energy storage.However,the electronic conductivity of this material is low,and its direct application in electrochemistry is not ideal.The main research contents of this paper are as follows:（1）Through a simple one-step high-temperature calcination of g-C₃N₄（CN）and magnesium powder,a lamellar structure g-C₃N₄ photocatalyst（NHCN）with partial broken hydrogen bonds and nitrogen defect is obtained.The hydrogen bonds in the NHCN structure are broken and the nitrogen in the N_2C lattice site is missing,giving it a unique electronic structure.The test results show that the synergistic effect of hydrogen bonds destruction and nitrogen vacancies can improve its photocatalytic hydrogen evolution activity.The hydrogen evolution rate of NHCN reaches 1941.7μmol h^-1g^-1,which is 13 times and 4 times that of CN and HCN.The excellent photocatalytic activity of NHCN is mainly attributed to the partial destruction of hydrogen bonds due to the loss of part of the NH_x in the layer,thereby improving the electron transportability and exposure of lateral edges and catalytic sites;nitrogen defects introduced on the surface of the material can act as electron traps can inhibit the recombination of photo-generated electrons and holes.（2）Using glucose as the carbon precursor and g-C₃N₄（CN）as the self-sacrificial template and nitrogen source,graphene-like nitrogen-doped porous carbon nanosheets（NPCN）were prepared by simple calcination.The material shows multifunctional applications,and can be used as an electrode material for lithium-ion batteries（LIBs）and a catalyst for oxygen reduction reactions（ORR）.Application in LIBs:at a small current density of 0.1 A g^-1,the first reversible specific capacity of NPCN-800 is as high as 1286 m Ah g^-1.At a high current density of 10 A g^-1,the discharge specific capacity of NPCN-800 remains at 258 m Ah g^-1,and after 200 cycles,it has a discharge capacity of 818 m Ah g^-1 at a current density of 0.2 A g^-1Excellent cycle stability.Compared with CN and PCN,NPCN-800 as a lithium-ion battery negative electrode shows more excellent electrochemical performance.In addition,the ORR catalytic activity research test shows that NPCN has good catalytic activity.This is mainly due to:nitrogen atoms increase the defects of the carbon skeleton during the doping process and increase the specific surface area of the material;in addition,the doped nitrogen species is mainly pyridine nitrogen,which can promote charge transfer.