| Electrochemical capacitors,also known as supercapacitors,are new energy storage devices between traditional capacitors and batteries,presenting the advantages of high power density,long-term cycling stability and fast charge-discharge property,which have attracted numerous attentions around the world.However,the greatest challenge for supercapacitors is how to improve the energy storage ability without compromising the rate capability.The electrode materiasl as the key component of supercapacitors,the architecture and composition is always the research hotspot for supercapacitors,especially for three-dimensional porous carbon-based nanomaterials.Electrospinning carbon nanofibers(CNFs)with ultra-long one-dimensional nanostructure and three-dimensional continuous framework not only can be applied to electrode materials directly,also can be served as substrates for pesudocapacitive materials deposition or heteroatom doping to further enhance the capacitance.On the basis of above,a series of investigations have been carried out as follows:(1)The CNFs as substrates,a large amount of PANI(78%)can be uniformly deposited on the surface of CNFs through repeated in situ chemical polymerization.The obtained CNFs/PANI composites as electrode matertials exhibit a high capacitance of 407 F/g at the scan rate of 5 mV/s in three-electrode configuration systerm.As known,dense CNTs decorated on CNFs can effectively reduce the ion diffusion length,improve the conductivity as well as the utilization of PANI.Thus,high-quality CNFs/CNTs hybrid carbon substrates have been fabricated by the combination of solvotherm reaction,hydrogeneous reduction and in situ chemical vapor depositon.The as-fabricated all-solid-state flexible supercapacitors based on CNFs/CNTs/PANI ternary composite electrodes present high energy density of 5.1 Wh/kg and power density of 10.1 kW/kg.(2)The PAN nanofibers with unique architecture of ultra-long one-dimensional nanostructure and three-dimensional porous framework are ideal substrates for acrtive materials deposition.By in situ chemical polymerization of aniline monomers,the PAN@PANI nanofibers can be successfully synthesized with a uniform and continuous core-shell nanostructure.The PAN@PANI nanofibers as electrode materials with an optimized acid doping state and mass loading have achieved a high specific capacitance of346 F/g at 5 mV/s in three-electrode system.It should be noted that the PANI in PAN@PANI nanofibers acts as both active materials for energy storage and conductiongpathways for electron transfer.Moreover,the PAN@PANI nanofibers with unique core-shell architectures are also ideal nitrogen-enriched precursors.Nitrogen-doped porous carbon nanofibers(NPCNFs)can be facilely fabricated by the pyrolysis of PAN@PANI nanofibers,on the surface of which the nitrogen content and porous structure can be easily controlled by adjusting the pyrolysis temperature.Benefiting from suitable nitrogen doping and abundant porosity of NPCNFs,the as-fabricated solid-state flexible device can achieve high energy and power density of 250 W/kg and 9.2 Wh/kg,respectively.Notably,the device still can deliver a high energy density of 5 Wh/kg even under high power density of5.8 kW/kg.(3)It is well known that porous carbon materials with high specific surface areas and low internal resistance can achieve desirable energy storage.The precursor solution of PAN/PVP/DMF results in the formation of porous PAN membrane in the presence of water due to the phase separation principle.Thus,hierarchically porous carbon(HPC)membrane with well-interconnected porosity and highly cross-linked conducting networks can be facilely fabricated through the carbonization and KOH activation treatment of the obtained PAN membrane.The as-assembled CR2025 coin devices based on HPC demonstrate high specific capacitance of 204 F/g and 152 F/g at 0.5 A/g and 32 A/g,respectively,as well as very low internal resistance of 0.8 Ω and high Coulombic efficiency of 96%.Obviously,the HPC as substrate decorated by PANI with additional pseudocapacitance can further improve the specific capacitance.Moreover,a very facile roult has been provided to fabricate integrated electrodes of nickel foam supported hierarchically porous carbon materials with favorable combination between the current collectors and active materials.Benefiting from the well-designed architecture of NF-HPC electrodes,the as-fabricated device possess a very low internal resistance of 0.31 Ω,high Coulombic efficiency of 100%,high specific capacitance of 283 F/g at 0.5 A/g,as well as high enegy and power density of 10 Wh/kg and124 W/kg,respectively. |
