Preparation Of Corn Protein-derived Porous Carbon And Performance Studying Of Its Zinc Ion Capacitor

Aqueous zinc ion hybrid supercapacitors（ZHSCs）are an emerging multivalent ion energy storage device that combines the advantages of high energy density,good safety,low cost,and environmental friendliness of zinc ion batteries with the high power density and superior cycling performance of supercapacitors.Therefore,ZHSCs are considered as a very promising new electrochemical energy storage system.Although the research on ZHSCs has made great progress in recent years,it is still in its infancy and faces many challenges.In particular,the suboptimal energy density of cathode materials and the mismatch between capacity and kinetics and battery-type anodes（usually zinc metal）have resulted in ZHSCs being unable to meet the growing performance demands of portable electronics and electric vehicles in the short term.Therefore,the development of low-cost,high-performance and long-life capacitive cathode materials is very urgent for current ZHSCs.Considering that carbon-based materials are widely used as electrode materials for electrochemical energy storage devices,especially carbon materials derived from biomass,which have the advantages of abundant sources,low production cost,good electrical conductivity,high chemical stability,and diverse and controllable microstructures,they have recently been widely studied and applied in Zn²⁺energy storage devices.It remains a great challenge for the joint development of ZHSCs and biomass carbon materials to select suitable precursors from abundant biomass sources and prepare high-performance carbon materials that can be used in ZHSCs electrodes by simple and excellent processes.In this thesis,a series of porous carbon materials with multi-scale pore structure and rich heteroatom content were prepared by combining two different heat treatments,rapid pyrolysis and hydrothermal carbonization,with chemical activation using corn protein powder rich in C,N and O elements as the source of biomass carbon materials.Two modification strategies,surface structure modulation and heteroatom doping,were adopted in the preparation process,making the prepared carbon materials suitable for the electrodes of symmetric supercapacitors（SCs）and ZHSCs.The optimum activation and doping conditions were explored by combining morphological characterization and electrical properties testing,and the effects of hole structure and atomic doping on the electrochemical properties of the materials were studied.The main contents are as follows:（1）O and N self-doped graded porous carbon materials with ultra-high specific surface area(2986.7 m²g^-1)and rich pore structure were prepared by pre-carbonization treatment combined with KOH activation strategy using fine maize protein powder obtained after treatment as carbon source.The surface structure and composition of the carbon material is adjusted by adjusting the ratio of activator during the preparation process.Two aqueous electrolytes,6M KOH and 2 M ZnSO₄,were used to assemble symmetric supercapacitors and zinc ion hybrid supercapacitors,respectively,and the effects of pore structure and self-doped atoms on their charge storage capacity were investigated.The appropriate activation conditions were also summarized.The assembled SCs and ZHSCs exhibited promising electrochemical properties.In particular,ZHSCs show an excellent energy density of 137.22 Wh kg^-1(corresponding to a power density of 100 W kg^-1)and a power density of up to40 kW kg^-1(corresponding to an energy density of 9.2 Wh kg^-1),and good cycling stability(98.91%capacity retention after 10,000 cycles at 5 A g^-1).（2）To improve the N and S content of the carbon materials,the N and S co-doped biomass porous carbon materials were prepared by high pressure hydrothermal pretreatment using thiourea as the source of heteroatoms together with corn protein powder,followed by a one-step carbonization activation method at high temperature.The effects of heteroatom doping on the morphological structure and electrical properties of carbon materials were investigated in depth,and it was found that the moderate addition of thiourea was beneficial to the formation of porous structure and the increase of heteroatom content,which could improve the electrochemical properties;however,too much dopant would lead to the destruction of the structure and thereduction of capacitance and multiplicative capacity.Thanks to the suitable doping ratio,the porous carbon materials produced have a high specific surface area(2616.7 m²g^-1),a well-developed porous structure and an abundant heteroatom content.The assembled SCs not only have an impressive capacity(232.2 F g^-1at 1 A g^-1),but also exhibit excellent cycling stability(100%capacity retention after 20,000 cycles at 5 A g^-1).The ZHSCs with very good performance were further assembled and showed good potential application prospects.They exhibit high zinc storage capacity(0.1 A g^-1,269mAh g^-1)and can provide energy densities up to 146 Wh kg^-1(corresponding to a power density of 200 W kg^-1),with a high energy density of 34.56 Wh kg^-1even at 40 kW kg^-1.