Preparation Of Transition Metal-nitrogen Co-doped Carbon Materials And Their Application In Oxygen Reduction And Supercapacitors

With the continuous development of society,energy issues have become a major issue in the development of society today.Fuel cells and supercapacitors are new tools for"capacity"and"storage".They have attracted the attention of materials and chemists because of their environmental protection and wide applicability.The pros and cons of material properties restrict the practical use and commercialization of fuel cells and supercapacitors.Carbon-based high-performance materials are excellent choices for cathode oxygen reduction catalysts and supercapacitor electrode materials for fuel cells because of their wide economic and environmental applicability.However,due to the fact that the surface of the carbon-based material forms large delocalized bonds,the structure is relatively stable,and the catalytic performance needs to be improved.In this dissertation,the transition metals（Fe,Co,Ni）and nitrogen were uniformly doped into carbon materials.Thermal gravimetric analysis（TG）,Fourier transform infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,and field emission scanning electron microscopy（FE-SEM）were used.The prepared material is characterized by geometric and electronic structures.Using CHI660E electrochemical workstation and RDE rotating disk electrode,the material was tested for cathode oxygen reduction（ORR）reaction and supercapacitor energy storage performance.The specific work is as follows:（1）Preparation of transition metal-nitrogen co-doped carbon material（MNC）.Using a mixture of transition metal nitrate and melamine as raw materials,the transition metal nitrate and the melamine monomer are uniformly mixed by ball milling,ultrasonic vibration,etc.,and then heat-treated at high temperature in nitrogen to prepare a co-doped transition metal and nitrogen.Carbon materials（MNCs）serve as precursors for the preparation of other materials.（2）Preparation,characterization and ORR performance of transition metal-nitrogen co-doped carbon nanotubes（M–N/C）.The M–N/C nanotube catalyst can be obtained by treating MNC with 15%hydrogen peroxide.The characterization results indicate that M–N/C material is a kind of carbon nanotube-type material co-doped with transition metal and nitrogen.Due to the surface treatment of hydrogen peroxide,its surface has more reactive functional groups than MNC,including pyrrole nitrogen,Pyridine nitrogen,transition metals–N,C≡N,etc.,were found in the ORR test to show that cobalt-nitrogen co-doped carbon nanotube catalysts（Co–N/C）performed better than nickel or iron–nitrogen co-doped catalysts（Ni–N/C or Fe–N/C）.In a 0.1 M KOH alkaline solution,the half-potential of the Co–N/C catalyst was as low as 832mV,close to the same Pt/C catalyst（slope potential 848 mV）,and the limiting diffusion current reached 6.0 mA/cm².The limit diffusion current is better than Pt/C 5.6 mA/cm².In addition,the material has good stability and shows better methanol resistance than Pt/C.Further,Co and Fe binary transition metal and nitrogen co-doped carbon nanotube material（CoFe–N/C）exhibited superior electrocatalytic stability.（3）Preparation of transition metal-nitrogen co-doped carbon material MNCC and its application in supercapacitors.The MNC material was activated by a chemical activation process to prepare a material MNCC with rich pores and high surface active sites.In the electrochemical test,the collector electrode made of CoNCC material has a single electrode specific capacitance of 167.5 F·g^-1 under cyclic voltammetry（CV）,which is superior to 137.2F·g^-1 and NiNCC of FeNCC.At 149.1 F·g^-1,the three materials showed higher single-electrode specific capacitance in the carbon-based alkaline supercapacitor electrode material.Cyclic voltammetric scans of 2000 were found to have high stability.