| Supercapacitors are drawing increasing attentions due to their capability of high power density and ultra-long cyclic life.However,the relative low energy density seriously restricts its development and applications.As the central component of supercapcitors,electrode materials determine its ultimate energy density in large extent.Therefore,the research on electrode materials is critical important.Compared to pseudo-capacitive materials,carbon materials possess unparalleled advantages including high surface area,low cost,good conductivity and excellent cyclic stability,permitting them promising prospects for application in supercapacitors.Nevertheless,relative low capacitance hinders its developments and applications.Thereby,this paper focused on heteroatoms doping modification and controllable preparation of two-dimensional nanostructural carbon materials to achieve advanced carbon electrodes with high capacitance and high rate capability.In addition,the effects of heteroatoms functional groups,microscopic structure and porosity on the performance carbon electrodes are investigated.The details are as follows:(1)Nitrogen-containing mesoporous carbon(NMC)has been fabricated through solvent-evaporation induced self-assembly using phenolic resin as carbon source,dicyandiamide as nitrogen dopant and tetraethyl orthosilicate as secondary pore-forming agent.The obtained NMC has a high surface area(1390 m2 g-1),reasonable pore size distribution(1.5-8.1 nm)and a relative high nitrogen content(4.7 wt.%).Appealingly,the NMC achieves a high specific capacitance of 238.4 F g-1 at a current density of 1 A g-1,and still can remain 180 F g-1 at 10 A g-1.The superior performance of NMC can be attributed to the high surface area,reasonable mesopore structure and nitrogen-doping.The high surface area combined with reasonable pore size distribution ensures high ion-accessible surface area and short ion transfer path.Furthermore,nitrogen doping improves the wettability of electrode,resulting in an enhanced ion-accessible area and decreased ion transfer resistance.(2)Two-dimensional structural carbon materials have high effective surface area and short ion transfer path compared with the bulk porous carbon.Herein,N,O-dual-doped two-dimensional carbon nanosheets(DGCNS)has been prepared through molten salt assisted method using glucose as carbon sources and urea as nitrogen source.The effect of heteroatoms functional groups on the electrochemical performance of DGCNS has been studied.Benefiting from the synergistic effect of two-dimensional nanostructure and heteroatoms functional groups,the optimized DGCNS700 exhibits high specific capacitance of 288 F g-1 at a current density of 0.5 A g-1,and a good rate capability with 160 F g-1 retention at 10 A g-1.(3)A nano-confined self-assembly strategy has been developed to synthesize ordered mesoporous carbon nanosheets(OMCNS).The montmorillonite with lamellar structure used as hard template provides a confinement self-assembly place.OMCNS possesses the advantages of two-dimensional nanostructure and ordered mesoporous characteristic,ensuring high ion-accessible surface area and facile ion transportation.Electrochemical test results show that the OMCNS exhibits excellent rate capability and superior cyclic stability in both aqueous and ionic liquid electrolytes.(4)Oxygen-enriched crumpled graphene(OCGN)with high density has been prepared through in-situ grown of ZnO followed by a low temperature thermal reduction process,aiming to realise high volumetric performance in addition to high gravimetric performance.OCGN possesses the advantages of high content of active oxygen functional groups(17.26 at.%)and high density(1.28 g cm-3),resulting in a high gravimetric and volumetric capacitance(300.5 F g-1,384.6 F cm-3).Furthermore,the assembled OCGN-based supercapacitors exhibit a high gravimetric and volumetric energy density of 20.4 Wh kg-1 and 26.1 Wh L-1,as well as an excellent cyclic stability with only 7.7% capacitance degradation after 10000 cycles. |
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