Preparation And Electrochemical Performance Of Carbon Nanomaterials Based On Waste Biomass

Although lithium-ion batteries have been commercialized successfully,they still have some shortcomings,such as bad charging and discharging performance under large current density,safety problems,high cost of raw materials,and poor long-term cycle properties.Therefore,the development of other new energy storage system s has important theoretical research and practical application value.Supercapacitors and zinc-air batteries are two important energy storage devices,which have a series of advantages,such as clean,excellent safety,high efficiency,low price,long cycle life and so on.They are expected to replace lithium ion batteries in some fields.Electrode material is the core component of the electrochemical energy storage device s,which is the key to further enhance the competitiveness of the new energy storage device s.Carbon nanomaterials have been widely used in chemical power sources because of their excellent electrical conductivity,high theoretical specific surface area and good plasticity.In this paper,the abundant and cheap waste biomass was taken as carbon precursors to prepare a series of new type of biomass-derived functional carbon composite materials through modification,doping,pyrolysis and other methods.As an electrode material for electrochemical energy storage device,its electrochemical properties,such as energy density,power density,rate performance and cycle stability,have been studied in depth,and some innovative research results as follows:(1)The waste biomass orange peel was used as carbon source,KMnO₄ was taken as oxidant and metal source,and dicyandiamide was used as nitrogen source,a new three-dimensional porous carbon composite loaded with MnO nano dots(MnO@NOPC)was prepared by pyrolysis.The specific surface area and the average pore diameter of MnO@NOPC are 812.27 m² g^-1 and 3.135 nm,respectively.The diameter of MnO nanoparticles is about 5 nm,and they are uniformly embedded in carbon nanosheets.And the interlayer spacing of carbon in MnO@NOPC expands to 0.395 nm,which is much larger than that of graphite(0.34 nm).When MnO@NOPC is used as the electrode material of symmetrical supercapacitors,it possesses high specific capacitance value,excellent rate performance and good cycle stability.The specific capacitance value is 327.86 F g^-1 at 1 A g^-1,the energy density value is 58.04 Wh kg^-1(about 12 times than that of commercial carbon-based symmetrical supercapacitors)at the power density of 296 W kg^-1,the capacitance retention of MnO@NOPC is 97.90%of its initial value and the coulombic efficiency is 90.45%after 10000 cycles at 2 A g^-1.(2)A novel self-doped porous carbon nanocomposite with N,O and P(PPBC)was prepared by using waste biomass pig bones as precursors.The abundant calcium phosphate and calcium oxide in pig bones were used as natural self-templates.After high temperature carbonization,the dilute nitric acid was taken as etchant.The results show that PPBC has a high specific surface area(785.70 m² g^-1)and suitable pore structure(the average pore diameter of PPBC is about 2.43 nm),and the contents of N,O and P are up to 6.36%,18.14%and 0.30%,respectively.The abundant pores and high percentage of heteroatoms greatly improve the electrochemical performa nce of PPBC in symmetrical supercapacitors:When 6 mol L^-1 KOH is used as electrolyte,the specific capacitance value of PPBC is 274.05 F g^-1 at 1 A g^-1,and the highest energy density was 49.31 Wh kg^-1(about 10 times than that of commercial activated carbon-based symmetrical supercapacitors)at the power density of 299.95 W kg^-1;When 0.8 mol L^-1 KPF₆ is used as electrolyte,the specific capacitance value of PPBC is 230.68 F g^-1 at 0.5 A g^-1,and the highest energy density is 400.46 Wh kg^-1(at the power density of 144.05 W kg^-1),which is about 2?4 times than that of commercial lithium ion batteries(about 100?200 Wh kg^-1).(3)The waste biomass pig bones were used as the precursors,FeCl₃ was taken as the iron source and the melamine was used as the nitrogen source.After two-step carbonization strategy,a three-dimensional(3D)porous bone carbon material loaded with iron nitride(Fe₃N and FeN_0.0324)nanoparticles(Fe_xN@PC)was obtained.The results show that the unique 3D laminar structure provides a large number of electron migration pathways.Fe₃N and FeN_0.0324 nanodots provide rich reactive centers,and promote the performance of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)simultaneously.In the ORR test with 0.1 mol L^-1 KOH as the electrolyte,the onset potential(E_onset)of Fe_xN@PC is 0.99 V,the half-wave potential(E_1/2)is 0.84 V,and the limit diffusion current density(J)is 6.43 mA cm^-2,all of which are better than that of the commercial Pt/C catalyst.Besides,the overpotential of Fe_xN@PC in OER is only 140 mV at 10 mA cm^-2,which is much lower than that of commercial Ru O₂ catalyst(330 mV).The rechargeable zinc-air battery built with Fe_xN@PC has an open-circuit voltage of 1.504 V,a high power density(P)of 223.67mW cm^-2 at a current density of 397.03 mA cm^-2,an ultra-high specific capacity of766.20 mAh g^-1 at 5 mA cm^-2,and superb cycle stability.