Preparation Of Biomass-based Capacitance Carbon And Its Electrochemical Performance

At present,the massive consumption of non-renewable fossil resources leads to the worsening of environment and frequent disastrous climate,the development of renewable green energy has become an urgent problem for all countries in the world.In recent years,wind energy and solar energy have become the most promising new energy sources for industrialization,but the instability of natural wind and solar energy has become the biggest obstacle for the development of new energy industry.Therefore,effective energy storage materials and devices are the key technologies out of the dilemma.Supercapacitors are considered as one of the most promising energy storage devices because of its high power and long cycle life.The key to improve the energy density is to optimize the electrode materials of capacitance.The purpose of this thesis is to improve the electrochemical performance and energy density of capacitance carbon by studying the preparation method.In this paper,biomass-based capacitance carbon was prepared by hydrolysis-activation method,and its electrochemical properties were improved by doping nitrogen and loading TiO₂modification.The hydrolysate produced by the hydrolysis step can be used as the raw material for producing furfural,thus reducing the discharge of the waste liquid.The concrete research results of this paper are as follows.1.Corncob-based activated carbon,rice husk-based activated carbon and orange peel-based activated carbon were prepared by hydrolysis-activation method.Corncob-based activated carbon was prepared by two-step method of hydrolysis-activation.The iodine adsorption value of corncob-based activated carbon was up to 1726.5 mg?g^-1,and the crude yield of activated carbon was 16.2%.During the hydrolysis process,the hemicellulose in the corncob structure was hydrolyzed and the structure of the hydrothermal carbon precursor become loose,the activator KOH can each into the hydrothermal carbon precursor and the activated carbon was prepared.The micropore ratio of activated carbon prepared by this method was only53.06%,indicating that a large number of mesoporous and/or macroporous existed in activated carbon.The hierarchical pore structure improved the electrochemical performance of the corncob-based capacitance carbon.Rice husk-based activated carbon was prepared by hydrolysis-activation method.The specific capacitance of activated carbon was 199 F?g^-1 when the current density was 0.5 A?g^-1,and the capacitance retention was 92.0%when the current density was increased to 20 A?g^-1.Orange peel-based capacitance carbon was prepared by hydrolysis-activation method.The relationship between structure and properties of orange peel-based capacitance carbon was revealed by investigating the effect of different activators on the electrochemical properties of the capacitance carbon.The larger microporous structure?1.3-1.8 nm?produced by H₃PO₄ activation not only provided a larger ion adsorption space,but also made an unblocked channel for ion transmission and transfer As a result of KOH etching,large pores were formed on the surface of the activated orange peel-based activated carbon,which increased the rate performance of the capacitance carbon and reduced the impedance of the electrode.2.Rice husk-based capacitance carbon was modified by nitrogen doping and TiO₂loading.The effect of modification methods and conditions on the electrochemical properties of as-prepared capacitance carbon was investigated.When cetyltrimethylammonium chloride?CTAC?was used as nitrogen source,the specific surface area and micropore ratio of the nitrogen-doped carbon increased.The prepared carbon with nitrogen-containing functional group had better electrochemical performance:the specific capacity was increased to 252 F?g^-1(5 mV?s^-1);At a current density of 20 A?g^-1,the capacitance retention rate was 71.7%;at a current density of 1 A?g^-1,the capacitance retention rate of the electrode was 90.7%after10000 cycles of constant current charge and discharge.Ethylenediamine was used as nitrogen source,the nitrogen doping of rice husk-based capacitance carbon was studied by microwave hydrothermal treatment and impregnation at room temperature,respectively.The contents of nitrogen were 4.43%and 3.55%respectively measured by element analysis,and the nitrogen in the framework was mainly pyrrole nitrogen.The results of electrochemical test showed that the electrochemical performance of the activated carbon prepared by microwave hydrothermal treatment was better than that of the activated carbon prepared by impregnation at room temperature.When the current density was 20 A?g^-1,the power density was 4685 W?kg^-1,and the energy density was 6.25 Wh?kg^-1.Rice husk-based activated carbon was loaded with TiO₂ through microwave hydrothermal assisted to increase the volume specific capacity of the capacitance carbon.Anatase TiO₂/AC and rutile TiO₂/AC composites were prepared by calcination at 500?and 700?,respectively.The specific surface area of activated carbon was decreased,but the specific capacitance increased after TiO₂ loading.The results of the CV test showed that the loaded TiO₂ has a pseudo-capacitance due to the redox.When the current density increased to 20 A?g^-1,the energy density of anatase TiO₂/AC remained at 6.9 Wh?kg^-1.3.The production of furfural using xylose solution instead of biomass hydrolysate was studied.In the reaction system of low water content,the reaction conditions of furfural production by dehydration of xylose catalyzed by NaCl were optimized,and the yield of furfural can reach 61.5%.While H-ZSM-5 zeolite was used as catalyst,the yield of furfural was 52.4%.