The Controllable Synthesis Of Crystalline Nanocarbon-based Materials And Their Electrochemical Performance For Energy Storage

With the depletion of the conventional energy sources and the severity of theenvironmental pollution in the twenty-first century, the researches of the new energymaterials and devices have been attracted considerable attentions in whole society. As akind of energy storage and conversion device, supercapacitors, which bridge the gapbetween the traditional capacitors and batteries, have received currently much interestbecause their wide range of applications in as portable electronics, hybrid electricvehicles, and pulsing techniques based on their virtues of the high specific capacitance,reliable cycle life, wide operating voltage, high energy and power density. Electrodematerial is the key that affected the electrochemical performance of supercapacitors.Among various electrode materials, carbon materials are the main electrode materialsfor commercial supercapacitors due to their high cycle stability. However, the lowcapacitance of traditional carbon-based electrode materials (activated carbons andcarbon nanotubes) still limited the improvement of their energy density. According tothe group interaction, we have designed and prepared a series of advanced carbonelectrode materials with special microstructures from different carbon resources forsupercpacitors. The main contents in this paper have been shown as follows:1. Porous crystalline carbons (PGC) were synthesized via a simple “Solution-Solid”route and their application as advanced electrode materials for supercapacitor were alsodemonstrated. The electrochemical tests prove that the PGC sample shows capacitivebehavior. The outstanding performance of the PGC sample is attributed to its specialmicrostructure. That is, the porous structure and high conductivity are favor forion-charge transport during the high galvanostatic charge-discharge process.2. An easy and effective one-step hydrothermal process was developed to preparenitrogen-doped grapheme (NGS) by a hydrothermal reaction of GO with urea. A seriesof experiments indicate that the surface area, nitrogen content and type of NGS materials could be controlled by adjusting the experiment conditions. The as-made NGSsample (mass ratio of urea/GO is300:1, hydrothermal temperature:180oC,hydrothermal time:12h) exhibits the best capacitive performance: high capacitance (326F/g,0.2A/g), superior cycling stability (maintaining initial capacity) after2000cycles.Most importantly, in a two-electrode symmetric capacitor, the energy density of25.02Wh/kg should be achieved at power density of7980W/kg. The experimental resultsfurther demonstrated that the types of nitrogen play an important role in the capacitivebehaviors. In detail, the pyridinic-N and pyrrolic-N could provide pseudo-capacitanceby the redox reaction, while quaternary-N could improve the conductivity of the NGSthat is favorable to the electrons transport.3. Nitrogen-doped porous crystalline carbon (NPGC) was prepared by means of asimple coordination-pyrolysis combination route, the effect of different carbonizedtemperature and different melamine content on the microstructure was also studied. Thetests indicated that the NPGC material has large surface area, well conductivity and highnitrogen content. The unusual structure of NPGC sample endows its superior capacitiveproperty. NPGC-2-900sample has high specific capacitance of293F/g at1A/g. Afterconsecutive5000cycles, the specific capacitance of NPGC-2-900still maintains theinitial capacity.4. The separated boron and nitrogen co-doping porous graphitic carbon (BNGC) wasfabricated though a hydrothermal coordination-ZnCl2activation process from nitrogen-containing chitosan. In this synthesis, chitosan was first coordinated with Fe3+ions toobtain the chitosan-Fe precursor. Followed by the hydrothermal reaction, H3BO3wasconverted into B2O3steam, which reacts with residual oxygen groups of chitosan-Fe.After that, the boron atoms doped into the skeleton of to get the separated B and Nco-doping polymerized carbon. After ZnCl2activation and removal of Fe catalyst withhydrochloric acid, the BNGC with high surface area was synthesized. Benefiting fromthe structure of BNGC samples and isolated boron and nitrogen co-doping, the BNGC sample exhibits high specific capacitance (313F/g,1A/g), well electrochemicalstability, high coulombic efficiency, high energy and power densities.5. The porous layered crystalline nanocarbon (PGNS) has been synthesized throughan effective simultaneous activation-graphitization route by using a renewable andinexpensive coconut shell. In the preparation, the graphitization catalyst precursor(FeCl3) and activating agent (ZnCl2) are simultaneously introduced into the frameworkof the coconut shell to get the coconut shell-Fe precursor. Following pyrolysis andremoval of the catalyst, the PGNS material obtained. The as-prepared PNGS sample hashigh surface area and well conductivity. The PNGS exhibits excellent capacitivebehavior. In aqueous electrolyte, PNGS sample has high specific capacitance, superiorcycle durability and Coulombic efficiency. Remarkably, in an organic electrolyte, PGNSalso shows outstanding electrochemical performance: an energy density of up to54.7Wh/kg can be achieved at a high power density of10kW/kg.