Preparation,Characterization And Electrochemical Performance Of Heteroatom Doped Porous Carbon

Supercapacitor,as a kind of high power and long cycle life of new type energy storage device,has received the widespread attention in many fields.Menawhile,electrode material is the key of the research carbon materials.Carbon materials is a common electrode materials,however it has lower capacitance and power density because of double layer energy storage mechanism.Therefore,in order to further improve the energy density of supercapacitor,aiming at the existing defects of carbon materials,in this thesis,we fabricated carbon materials as electrode,which has excellent electrochemical performance by heteroatom doping modification and activation.At the same time,we also explored the influence of heteroatom doping and its microstructure on the performance of carbon material electrochemical devices.The main contents as follow:（1）Using the rose multiflora as a raw material and KOH as an activator,the carbon rich material with microporous and mesoporous multistage structures are prepared,and its specific surface area is up to 1646.7 m² g^-1.The electrode materials multistage pore structure provides faster transmission of electrons to the electrolyte.After activation,the content of nitrogen is 1.2%.Nitrogen doping can improve the electrical conductivity and material wettability of carbon material.In 6 M KOH aqueous solution,when evaluated as electroactive material for electrochemical supercapacitors,the rose multiflora carbon electrode(5 mg cm^-2)yields large gravimetric/volumetric specific capacitancs of³40.0 F g^-1(²38.0 F cm^-3)at 0.5 A g^-1.Besides,in the organic electrolyte（1 M TEABF₄/PC）,a greater energy density can be obtained.The energy density of the capacitor is 52.6 Wh kg^-1.Meanwhile,it has good cycling performance,even it can remain 96.6%after 6500 cycles.（2）One-step preparation of PVA-KOH gel polymer,KOH as an activator,after high-temperature carbonization,the carbon material has a rich and uniform pore structure and oxygen-containing functional groups.The physical properties indicate that the PVA-KOH gel polymer-derived carbon（POC-K）has a high specific surface area(1084.8 m² g^-1),a multi-order pore structure（mesoporous ratio 45.3%）,and an oxygen content of 6.0 at%.Electrochemical tests show that when the current density is 0.5 A g^-1,the mass specific capacity of the electrode with a loading of 5 mg cm^-2in the alkaline electrolyte is 256.7 F g^-1;when the current density rose to 10 A g^-1,the gravimetric specific capacitance(186.0 F g^-1)remained at 72.46%.It means that POC-K has good rate performance due to its high mesopores ratio.The greater gravimetric specific capacity(406.1 F g^-1)is produced in the acidic electrolyte due to the oxygen-containing functional group providing tantalum capacitance in the acidic electrolyte.At the same time,POC-K also exhibits a good reversible specific capacity(250 mAh g^-1at a current density of 100 mA g^-1)as a negative electrode material for sodium ion batteries.（3）Polyacrylamide hydrogel was used as a precursor,and N/P and N/S elements were doped by freeze-drying to obtain N/P co-doped porous carbon material（HNPC-F）and N/S co-doped heteroporous carbon material（HNSC-F）.The freeze-drying method is not only simple and environmentally friendly,but also can better preserve the morphology of the material itself and loose pore structure.According to physical properties,HNPC-F and HNSC-F possess high specific surface area(813.3;1192.1 m² g^-1)and multi-hole structure.The N\P,and N\S contents of HNPC-F（N:7.1%;P:0.42%）and HNSC-F（N:7.1%;S:0.8%）after doping increased,so that the HNPC-F and HNSC-F have good electrochemical properties.When the current density is 0.5 A g^-1,the gravimetric specific capacitances of HNPC-F and HNSC-F electrodes with a loading of 5 mg cm^-2are 284.7 and 325.8 F g^-1in the acidic electrolyte,respectively.In addition,HNPC-F has a large potential window（0.0¹.3 V）due to the doping of P atoms in the alkaline electrolyte,and its energy density is 10.3 Wh kg^-1at a power density of 325 W kg^-1.When HNPC-F and HNSC-F are used as negative electrode materials for sodium ion batteries,it also exhibits good electrochemical stability(reversible specific capacities are 88.0 and138.5 F g^-1,respectively,after 500 cycles at a current density of 50 m A g^-1).