Synthesis And Capacitive Performance Of Vanadium Nitride/carbon As Negative Electrode Materials Based On C₃H₆N₆

This work focuses on the preparation of a series of vanadium nitride and carbon composites used as negative electrode materials for supercapacitor based on melamine.The main methods used include mechanical mixing in solid-state,blending in liquid-phase and self-assembling in molecular point.(i)Firstly,vanadium nitride and carbon nanoparticles composites(VN/PCNPs)are fabricated by a pyrolysis process at high temperature for the mixture,in which V2O5 xerogel is used as vanadium source and mixed with C3H6N6 mechanically in solid state.The effects of the mass ratio between V2O5 and C3H6N6 combined nitrogen flow rate on the microstructure and electrochemical performance are also investigated.It is found that the as-synthesized VN/PCNPs are nanoparticles with a size about 25 nm.Both mass ratio and N2 flow rate have greater impacts on morphology and microstructure of products,which correspondingly determines the electrochemical performance of the material.The VN/PCNPs exhibits outstanding capacitive properties,and a maximum specific capacitance of 255.0 F/g is achieved at a current density of 1.0 A/g in 2 mol/L KOH aqueous electrolyte and the potential range from 0 to-1.15 V.(ii)Furthermore,ultra-small vanadium nitride quantum dots embedded in porous carbon(VNQDs/PC)are fabricated by a thermal treatment process for the mixture obtained after using NH4VO3 as vanadium source and blending with C3H6N6 at liquid phase.The electrochemical tests demonstrate that when mass tatio of NH4VO3/C3H6N6 reached 1: 7,VNQDs/PC exhibites a high capacitance of 281 F/g at a current density of 0.5 A/g.(iii)In order to seek better material structure,C3H6N6-NH4VO3 coordination polymer nanobelts were synthesized through self-assembly strategy by using NH4VO3 as metal centre of vanadium,and using C3H6N6 both as organic ligands and organic nitrogen reagent.In addition,vanadium nitride and carbon nanobelts(VN/PCNBs)are prepared after a heat-treatment process for the synthesisted coordination polymer with temperature programmer under nitrogen.Nanobelts with a length of 0.1~0.15 mm constantly grow outwards from many central growing point and more grow outwards smaller the nanobelts;the colder precipitation temperature and the bigger temperature difference lead to the formation of coordination polymer.When cooling rate is slow the obtained nanobelts with some defects and a length of 250 ?m,far less than the length(>1000 ?m)of nanobelts prepared under fast cooling rate.Stirring has a significant impact on the structure for the obtained coordination polymer.When the continuous stirring is applied during the process of fast cooling from 60 °C drop down to 0 °C,the synthesized final products after heat treatment exhibits foliated structure similar to the spindle(VN/PCNF).The electrochemical tests demonstrated that VN/PCNB and VN/PCNF exhibited capacitance of 266.3 F/g and 313.7 F/g at a current density of 0.5 A/g,respectively.And they still display high capacitance rention of 78.3% and 71.1% even the current density increased to 5 A/g.On the basis of study above,asymmetric supercapacitor was fabricated by selecting VNQDs/PC as negative electrodes combined Ni(OH)2 as positive electrodes.Remarkably,at a power density of 828.7 W/kg,the device delivered higher energy density of 47.2 Wh/kg.