Synthesis Of Hierarchically Porous Nitrogen-Containing Carbon And Its Electrochemical Capacitive Energy Stroge

Carbon-based material such as activated carbon, aerogels, nanostructures, graphene, used as capacitor electrodes and lithium batteries electrodes have attracted enough attention due to their low cost, availiablity, and wide ranging propeities. Carbons chemically modified with functions groups such as nitrogen, sulfur, phosphorus, boron, represent a very well defined region of preudocapacitance properties due to the faradaic redox reaction and modify the crystalline structures of the carbon host and results into the formation of defect in the structure that can provide more active binding sites for lithium adsorption. Conducting polymers (polyaniline, polypyrrole, polythiophene) used as nitrogen-containing carbon precesor and followed by activation have been reported used as capacitor electrodes electrodes. Graphene with a maximum theoretical capacity of 740 mAh g-1 on the basis of double-layer adsorption configuration, has been expected to be good candidate materials due to their ultra-large specific surface area, excellent electrical conductivity, high lithium ion storage capacity, and short lithium ion diffusion distance. In the thesis, various morphology polypyrrole have been synthesized and followed by carbonization-activation. Polyrrole/GO composites also have been synthesized by the in-situ chemical polymerization of pyrrole on both surfaces of graphene oxide combined with high temperature carbonization. The main results are concluded as follows:1. Nitrogen-containing activated carbon nanofibers (ACN) have been synthesized by one-step carbonization and simultaneous activation of polypyrrole (Ppy) nanofibers using ZnCl2 as activating agent. SEM images reveal that the ACN show interconnected fibrillar morphology, which are similar to that of the Ppy precursor. High-resolution TEM image reveals that the amorphous state and worm-hole type porosity of uniform meso/micropores structure which may be generate as a result of ZnCl2 activation. The ACN possess meso/microporous structures, high specific surface area (1062.22 m2g-1), high nitrogen content (8.47 at.%), and low oxygen content (5.25 at.%). As expected, the ACN exhibit enhanced capacitance performances compared with nitrogen-containing carbon nanofibers (CN), such as high specific capacitance (290.2 F g-1 at 0.5 A g-1), excellent rate capability (180.5 F g-1 at 50 A g-1), and good cycling stability (97% of capacitance retention after 1000 cycles at 10 A g-1). The excellent rate capability of the ACN electrode can be attributed to its high nitrogen content, high specific surface area and well-developed meso/microporous structure, which lead to high level of pseudocapacitance and facilitate the diffusion and migration of electrolyte ions.2. Nitrogen-containing carbon/graphene composite (CGC) nanosheets have been synthesized by the in-situ chemical polymerization of pyrrole on both surfaces of graphene oxide combined with high temperature carbonization. The CGC nanosheets show high specific surface area (106.22 m2 g-1), large pore volume (0.382 m3 g-1), and high nitrogen content (7.86 at.%). The nitrogen-containing carbon coating with low graphitization degree on both sides of graphene can prevent effectively from the aggregation of graphene oxide during its thermal reduction process. When evaluated for lithium storage capacity, the CGC nanosheets exhibit enhanced electrochemical performances in comparison with polypyrrole derived nitrogen-containing carbon (NC) nanoparticles, including high reversible capacity (651.5 mAh g-1 at 1A g-1), excellent rate capability (363.7 mAh g-1 at 10 A g-1), and good cycling stability (100% capacity retention after 100 cycles at 1A g-1). The high lithium storage performances of the CGC electrodes can be attributed to the high electronic conductivity, abundant lithium adsorption sites, and short diffusion distance of lithium ions arising from the CGC nanosheets with nitrogen-containing carbon on both sides of graphene.3. Three-dimensional hierarchical porous graphitic carbon (HPGC) have been prepared via simultaneous activation and catalytic route using polypyrrole as carbon precursor and potassium hydroxide (KOH) and nickel acetate (Ni(OH)2) as activating agent and catalyst, respectively. XRD spectroscopy analyses indicate that the HPGC materials were well graphitized. The obtained HPGC materials have a maximum specific surface area of 2489.2 m2 g-1, a large pore volume of 1.61 cm3 g-1, a micropore volume of 0.4 cm3 g-1, and an average pore diameter of 2.9 nm. As electrode material for supercapacitor, the HPGC exhibit a charge storage capacity with a specific capacity of 350.2 F g-1 in 1M H2SO4 at a current density of 0.5 Ag-1, retained 260 F g-1 at a current density 20 A g-1, and excellent rate capacity (64.7% retention ration even at 50 A g-1). Moreover, the cycling stability was quite well without decay after 1000 cycles. The electrochemical performance coupled with a facile synthesis procedure making HPGC as promising electrode material for supercapacitor application.