Biomass Carbon And Composite Material For Supercapacitor Applications

The supercapacitor is a kind of green energy storage device whose performance is between the traditional capacitor and the secondary charging battery,has the characteristics of long cycle life,high power density,short charging time and wide operating temperature range.Electrode materials are the core components of supercapacitor.In recent years,the research on improving the capacitance performance of supercapacitor by preparing reasonable electrode materials has become the attraction of researchers.Biomass carbon used for double-layers supercapacitor electrode material is obtained by common crop waste-rice husk as the precursor of biomass carbon by the regulation of preparation technology.Then,the biomass carbon/MnO₂ composite material was prepared in a binary composite form to increase the specific capacitance of the carbon material.The main content of the paper is as follows:1.Hierarchical micro-/mesoporous carbon derived from rice husk can be obtained by hydrothermal in NaOH solution or deionized water undergoing carbonization and activation with KOH.Through physical characterization,it can be seen that the degree of graphitization and the number of mesoporous of the carbon material after hydrothermal reaction pretreatment has increased.The highest surface area of HMMC-_NaOHaOH obtained by hydrothermal pretreatment with NaOH solution was around 2850 m²·g^-1,and the mesoporous ratio reached 49.3%.In 6 M KOH,HMMC-_NaOHaOH can obtain a specific capacitance of 302 F·g^-1,and had the highest specific capacitance.After 5000 high-current charge-discharge cycles,the specific capacitance retention rate approaches 90%.2.The rice husk pretreated with hydrothermal solution of NaOH solution is used as a carbon source,to prepare biomass carbon materials and used for the study of double layer supercapacitor electrodes by carbonization-activation process.Potassium hydroxide,Potassium acetate,potassium citrate and potassium carbonate as activators.The effect of different activators on the topography of carbon materials was analyzed by characterization.According to the Nitrogen adsorption/desorption isotherms,RHC-KOH and RHC-KAC have the largest specific surface area and the largest number of mesopores.Electrochemical test results show that the specific capacitances of RHC-KOH and RHC-KAC are the highest in the 6 M KOH electrolyte,reaching302 F·g^-1 and 308 F·g^-1,respectively.At the same time,the retention of capacitance is also the best after charge-discharge cycles.It is also understood that the change in specific capacitance of the pore size of micropores under different current densities,thus highlighting the promote of preparing high specific capacitance eletrode material for suoercapacitor from rice husk.3.Biomass carbon/MnO₂ composites materials were prepared by in situ growth method using activated carbon RHC-KOH and RHC-KAC as carriers.SEM is used to observe the growth mode of MnO₂.The functional groups of the materials and the valences of Mn elements were analyzed by XPS.Nitrogen adsorption-desorption curves were used to analyze the specific surface area and pore size distribution of the composites materials.the specific capacitance of the composite materials increases by approximately 80 F·g^-1compared to biomass carbon in 1 M Na₂SO₄ solution,and the advantages of the cyclic stability is preserved.