Tuned Preparation Of Biomass-derived Carbon Materials And Their Application In Zinc Ion Supercapacitors

To address the intermittent instability of new energy sources（solar,water,tides,etc.）,advanced energy storage are in urgent needed.As new energy devices,hybrid supercapacitors can combine the advantages of batteries and supercapacitors to provide high energy density,long cycle life and high power density,which attract immense attentions.As the core components,electrode materials determine the electrochemical performance,which need tremendous efforts to develop and optimize them.In recent years,porous carbon materials have occupied an important position in the development of zinc ion hybrid supercapacitors due to their large specific surface area and high electrical conductivity.Biomass-derived carbon materials are the primary choice due to their abundant sources and low cost.Generally speaking,the porous structure provides more channels and facilitates rapid ion transport;heteroatom doping can improve the pseudo-capacitance to contribute extra capacitor.As results,increasing the porosity of carbon materials and performing heteroatom doping are key factors to improve the energy storage of capacitors.In this paper,the electrochemical performance of three types of biomass-derived porous carbon materials in three-electrode systems and zinc ion hybrid supercapacitors are investigated by adjusting the pore structure and introducting heteroatom doping.The specific studies are as follows:1.Nitrogen-doped porous carbon materials（NPCs）were obtained by using lucerne as a raw material and as a carbon.The NPC-850 obtained at 850°C presented a high specific surface area of 1846.73 m²g^-1and a nitrogen content of 1.82 at%.The sample was shown to have a specific capacity of 200.2 F g^-1(0.5 A g^-1)and maintain an initial specific capacitance close to 100%after 10,000 cycles when applied as supercapacitor electrode in a three-electrode system.In addition,the zinc ion hybrid supercapacitor consisting of NPC-850 as the positive electrode and zinc flakes as the negative electrode was still able to provide an energy density of 26.2 Wh kg^-1at the power density of 8021.5 W kg^-1,which could light up a red LED bulb for about 5 minutes,demonstrating its practical value.2.Nitrogen-doped porous carbon materials（NACs）were obtained by direct high-temperature carbonization in air using recycled yeast cell walls as the carbon source,urea as the nitrogen source and the addition of salts mixture of KCl and Na Cl to cover the seal.The results show that the molten salt has both an activating effect and can modulate the structural morphology of yeast cell walls,transforming the spherical yeast cell walls into a two-dimensional structured activated carbon material in the form of sheets.At the same time,the material is rich in oxygen-containing functional groups and was tested electrochemically as an electrode material in a three-electrode system and in a zinc ion hybrid supercapacitor.In addition,NAC-20 cathode exhibited a high energy density of 37Wh kg^-1at a power density of 91 W kg^-1when assembled into a zinc ion supercapacitor.3.The carbon precursor is originated from mangosteen shells,which was crushed and undergo the heat treatment process at high temperature under a nitrogen atmosphere.After activation of the carbon precursor,thiourea was added into it as the sulphur source,which was homogeneously mixed and calcined again under nitrogen atmosphere to obtain sulphur-doped porous carbon materials（NSACs）.Electrochemical test results demonstrated that the NSAC-1.0 electrode exhibited a specific capacitance of 172.4 F g^-1at a current density of 1 A g^-1.Electrochemical tests on the assembled NSAC-1.0//2 M Zn SO₄//Zn Zn ion hybrid supercapacitor showed that the device was able to exhibited a capacity of 194.6 F g^-1at a current density of 0.5 A g^-1,while at power density of 160.1 W kg-1 at a high energy density of 69.2 Wh kg^-1,and an energy density of 22.8 Wh kg^-1at a high power density of 6566.4 W kg^-1.The NSAC-1.0//2 M Zn SO₄+1 M Na₂SO₄//Zn zinc ion hybrid supercapacitor was assembled through electrolyte modification optimization,which significantly improved the dendritic phenomenon on the surface of the zinc negative electrode.This provides a new strategy for exploring the development of more efficient zinc ion hybrid supercapacitors.