| In recent years,with the intensification of energy shortage and environmental crisis,the development of clean,efficient and sustainable energy sources has become increasingly important.Therefore,the development of energy storage equipment has received more and more attention,and the exploration of sustainable energy and efficient energy storage equipment has become an urgent problem for researchers to solve.As an advanced new type of energy storage device,supercapacitors can not only be used alone,but also be used in combination with other devices,to improve the overall performance and life of energy storage devices.Therefore,they have the greatest potential and an increasingly important role in the energy storage industry.Porous carbon materials are the most commonly used electrode materials for supercapacitors.The exploration of porous carbon materials is important for the development of supercapacitors.Due to the advantages of environmental protection,renewable,easy availability and high yield,biomass is promising carbon precursors for sustainable energy storage equipment.Biomass-derived carbon materials have attracted much attention because of their simple,low-cost,green,and pollution-free preparation process.However,the pore structure of carbon materials obtained by direct carbonization of biomass is mainly micropores,which lack sufficient mesopores and macropores to provide fast transmission channels for electrolyte ions,resulting in a large recession in the utilization rate of micropores used as energy storage space.Therefore,the development of hierarchical porous carbon materials with micro-/meso-/macro-pores is crucial to improve the capacitance performance.The pore structure of biomass-derived carbon can be adjusted by combining carbonization,activation and other technologies.In addition,related studies have shown that doping heteroatoms such as boron（B）,nitrogen（N）,phosphorus（P）and sulfur（S）in the carbon matrix can improve the electrochemical properties of the carbon electrode.In most cases,heteroatomic doping is achieved for biomass-derived carbon without additional dopants due to the presence of heteroatoms in the carbon source.Soybean protein isolate（SPI）extracted from soybean contains rich N and O elements,which is a low-cost,renewable and environmentally friendly carbon precursor.In this thesis,porous carbon electrode materials rich in heteroatoms were prepared by carbonization SPI with different porogenic agents.The specific research contents and results are as follows:（1）Preparation of Zn Cl2 activated SPI-derived porous carbon and the study of its capacitive properties.Using SPI as the carbon source and nitrogen source and Zn Cl2 as the activator,a series of N,O co-doped porous carbon materials were prepared by pyrolysis the mixture of SPI and Zn Cl2with different mass ratios at 850℃（SPI:Zn Cl2=1:0,2:1,1:1,1:2 and 1:3）.The effects of different mass ratios on the microstructure and capacitance performance of carbon sheets were also investigated.The addition of Zn Cl2 changed the morphology of carbonized samples from irregular bulk particles to flakes.With the increase of Zn Cl2 content,the SSA of the samples increased at first and then decreased.Moreover,the N,and O doping amount of the sample was increased by the activation of Zn Cl2.When the mass ratio of SPI to Zn Cl2 was 1:2,the SSA of the carbonized sample（NC-3）was the largest.Especially,it has superior electrochemical performance.In the measurement of the two-electrode system,the maximum specific capacitance of 117.62 F g-1 could be reached at 0.1 A g-1.The maximum energy density can reach 16.27 Wh kg-1.（2）Investigation of the capacitance performance of SPI-derived hierarchical porous carbon by the chemical foaming method of Zn（NO3）2·6H2O.Moreover,the optimal activation ratio and carbonization temperature were explored.Using SPI as the precursor and Zn（NO3）2·6H2O as the foaming agent and multi-functional agent,a series of N,O co-doped hierarchical porous carbon with different mass ratios and carbonization-activation temperatures were prepared.The effects of the amount of Zn（NO3）2·6H2O and carbonization temperature on the microstructure were studied.Furthermore,the electrochemical performance was tested and analyzed by assembling three-electrode system and symmetrical supercapacitor,and the charge storage mechanism was discussed.Unlike the morphological changes brought by Zn Cl2 to the samples,Zn（NO3）2·6H2O is necessary to form hierarchical porous structures.The large amount of mixed gas generated by its pyrolysis drives the raw material to expansion and foaming,and the Zn particles resulting from the thermal reduction of carbon act as a template after being removed by acid washing,leaving new pores,and thus the porous carbon pore structure of Zn（NO3）2·6H2O-assisted synthesis is obvious.The NC-1.5 synthesized at the optimum ratio（2:3）and carbonization temperature（850℃）has the largest SSA(1350 m2 g-1)and the most outstanding electrochemical performance.In the three-electrode system,NC-1.5 has good rate performance,the specific capacitance is 248 F g-1 and 109 F g-1 at0.5 A g-1 and 100 A g-1,respectively,and after 20,000 cycles at 150 A g-1,the capacitance retention is 94.2%.（3）Mixed nitrates-assisted built-in dual-template preparation of SPI-derived hierarchical porous carbon and the study of its capacitive properties.On the premise of the most suitable mass ratio of SPI to nitrate and the optimal carbonization temperature,the heteroatom doped hierarchical porous carbon nanosheets were prepared by replacing part of the Zn（NO3）2·6H2O with Fe（NO3）3·9H2O.The effects of different proportions of Fe（NO3）3·9H2O on the morphology,structure,and electrochemical properties of the prepared materials were revealed.Thus,the appropriate input amount of Fe（NO3）3·9H2O was concluded.The three-electrode system assembled with CZn Fe-5 electrode has a specific capacitance of 271 F g-1 at a low current density of 0.2 A g-1 and retains about 50%of the initial capacitance(133 F g-1)even at a current density of 100 A g-1 The maximum energy density of the CZn Fe-5//CZn Fe-5 symmetrical supercapacitor is 16.83 Wh kg-1.Even at the power density of 8.56 k W kg-1,the energy density can retain 9.73Wh kg-1. |
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