| Supercapacitor is a novel energy storage device between traditional capacitor and battery.Supercapacitor possesses a high energy density compared to traditional capacitor,and a high power density and a long cycle life compared to battery.Carbonaceous materials are widely used as supercapacitor electrode materials.The preparation of porous carbon materials with high specific surface area and flourishing porous microstructure has been attracted increasing attention.Biomass material is a preferred carbon resouce to prepare porous carbon materials for its renewable,easy visible and low-price.In this work,we prepared a series of porous carbon materials（PCMs）with excellent electrochemical performances using soybean strawas carbon source,then the PCMs were characterized using scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,physical adsorption apparatus,X-ray diffractometer（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy（Raman）,and contact angle measuring instrument.The research contents and results are as follows:（1）Soybean straw was firstly subjected to hydrothermal pretreatment using nickel nitrate as catalyst affording to interconnect nanometer sheets,then porous interconnected carbon nanosheets（PICNs）were prepared by the carbonization and KOH activation of interconnect nanometer sheets.The effects of hydrothermal temperature,time,and the ratio of nickel nitrate to soybean straw on the electrochemical properties of PICNs in detail.The results show that the unique sheet structure,high specific surface area and appropriate heteroatom content of PICNs ensure the rapid continuity of electrolyte ions in and out of the electrode materials,which is beneficial to improve the electrochemical performance of carbon materials.The specific surface area and average pore diameter of NNiSSC-400-700 are 2223 m2 g-1 and 1.89 nm,and its N and O contents are 5.08%and 9.4%,respectively.NNiSSC-400-700 possesses a high specific capacitance of 407 F g-1 at a current density of 0.5 A g-1 in a three-electrode system,and still has a high capacitance retention rate of 78.62%when the current density increase to 20 A g-1.After 10,000 charge/discharge cycles,the retention rate of the capacitor exceeds 93%,indicating the excellent cycle stability and reversibility of NNiSSC-400-700.Moreover,NNiSSC-400-700 possesses an energy density of 36.11W h kg-1 at a power density of 517.8 W kg-1 in a two-electrode system test,and a high retention rate of 87.5%after 10,000 cycles,indicating its excellent cycle stability and hig energy density.（2）Interconnected porous carbon nanosheets（IPCNs）were fabricated by a facile co-hydrothermal pretreatment,subsequent KOH activation procedure,using soybean straw as a carbon precursor and urea as a nitrogen source.The influence of the mass ratio of urea and soybean straw on the overall structure,pore size distribution and surface element composition of IPCNs and the effect of activation temperature on the carbon skeleton and pore size distribution of IPCNs were investigated in detail.The results show that the unique pore distribution structure of IPCNs provides more active sites and interconnected ion transmission paths,which is beneficial to improve the electrochemical performance of carbon materials.The specific surface area of N1SSC-700 is as high as 2631 m2 g-1 with a total pore volume of 1.23 cm3 g-1,and the N and O doping amounts are 3.02%and 13.84%,respectively.The suitable heteroatoms doping content in IPCNs is not only beneficial to shorten the time of electrolyte solution wetting the electrode material,but also increase its pseudocapacitance.Therefore,N1SSC-700 possesses a high specific capacitance of 325 F g-1 in a three-electrode system and of 161 F g-1 in a two-electrode system,and shows an excellent rate capacity and a cycle stability.Moreover,the energy density of N1SSC-700 is high up to 22.36 W h kg-1 at a power density of 0.51 KW kg-1.The paper has 56 figures,11 tables and 154 references. |
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