Synthesis And Capacitance Properties Of N-doped Porous Carbon/nickel-cobalt Oxides/carbon Micro-nanotubes Composite Materials

With the rapid development of new energy sources,supercapacitor energy storage devices have become indispensable,especially in some new industries,such as new energy vehicles.The performance of a supercapacitor are rmainly decided by electrode materials.At present,commercial carbon electrode materials have a problem that the capacitance is not high enough.In order to obtain excellent electrode materials,in-situ polymerized coal-based polyaniline is used as a carbon and nitrogen source,nickel acetate and cobalt oxalate are used as pyrolysis catalysts presoma,and nickel and nickel acetate are used as growth catalysts presoma of carbon tube.The carbon micro-nanotubes and N-doped porous carbon/nickel(cobalt)composites are simultaneously synthesized by a two-stage iurnace process.After metals are ionizied in the mixture consisting of carbon micro-nanotubes,N-doped porous carbon/nickel oxide cobalt and N-doped porous carbon/nickel oxide cobalt/carbon micro-nanotube composites were prepared by hydrothermal method and urea direct precipitation method,respectively.The structure and capacitance performance of composites are systematically studied,the results are obtained as follows:N-doped carbon micro-nanotubes were successfully prepared by two-stage furnace process and chemical vapor deposition.Nitrogen was incorporated into the carbon tube in the state of graphitized nitrogen.The prepared carbon micro-nanotubes have various shapes,such as straight tubes,curved tubes,bamboo-like shapes,and sugar gourd strings.The tube diameter ranges from 10 to 100 nm,the tube length ranges from a few hundred nanometers to several tens of micrometers,and the tube wall thickness is 10-15 nm.Its growth modes mainly include"low-end growth","top growth","both ends grow",and "bamboo-like growth".When nickel acetate was used as the pyrolysis catalyst and growth catalyst,the carbon tube yield was the highest,which was 9.36 g/1 g nickel acetate/320 g coal-based polyaniline.When the ferrocene is used as a growth catalyst,the quality of the carbon micro-nanotubes is better.N-doped porous carbon/nickel-cobalt oxides/carbon micro-nanotube mesoporous composites with an average pore diameter of 8.4 nm were successfully synthesized by hydrothermal method.The metal oxide mainly exists in the form of NiCo2O4 and NiO,which presents hexagonal nanosheets adhering to the surface of the porous carbon in the form of a hexagonal nanolayer sheet.When the mass ratio of N-doped carbon/nickel to N-doped carbon/cobalt was 1:2,the carbon micro-nanotube doping amount was 10%,and the reaction condition is 120?,12 h,the obtained N-doped porous carbon/nickel-cobalt oxides/carbon micro-nanotube composites have a good wettability in aqueous electrolytes,and has the best capacitance performances,such as high specific capacitance,good rate capability and cycling stability.The specific capacitance is 847.4 F/g at 1 A/g.The capacitance retention rate was 81.1%after 5000 GCD cycles at 5 A/g.The N-doped porous carbon/nickel oxide cobalt/carbon micro-nanotube mesoporous composite with an average pore diameter of 56.3 nm was successfully synthesized by urea direct precipitation method.The nitrogen incorporated in the porous carbon was mainly present in the state of pyrrole type nitrogen and oxidized type nitrogen.The metal oxide was mainly present in the form of NiCo2O4 and adhered to the surface of the porous carbon in a nanoflower form.When the mass ratio of N-doped carbon/nickel to N-doped carbon/cobalt was 1:2,the carbon micro-nanotube doping amount was 10%,and the reaction condition was 80?,6 h,the obtained N-doped porous carbon/nickel-nickel oxides/carbon micro-nanotube composite has good wettability with the aqueous electrolyte,and has the best capacitance performance,high specific capacitance,good rate characteristics and cycle stability.At 1 A/g,the specific capacitance is 992.4 F/g.At 5 A/g,after 3000 cycles,the capacitance retention rate was 84.5%.Taking it as the positive electrode and activated carbon as the negative electrode,the assembled asymmetric supercapacitor has the characteristics of electric double layer and Faraday capacitance.At 1 A/g,the specific capacitance can reach 120.3 F/g,and the energy and power density are 16.7 Wh/kg,500 W/kg.