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Abstract: Carbon nanofibers (CNFs) were fabricated by thermal treatment of electrospun nanofibers obtained from precursor blends of polybenzimidazole (PBI) and Matrimid®. The microcarbon structures of CNFs obtained from PBI, and the 50:50 and 75:25 blends were studied using XRD and Raman spectra. Nitrogen adsorption/desorption measurements revealed that surface area and porosity of CNFs increased with an increase in Matrimid® content. Electrochemical performance of these CNF electrodes was studied for their application in energy storage devices. The CNFs from the PBI/Matrimid® (75:25)-precursor blend showed the lowest electrochemical impedance, and highest specific capacitance (111F/g) and energy and power densities of 24 and 6kW/kg, respectively. Steam activation and annealing further enhanced the performance resulting in a specific capacitance of 126F/g, and energy and power densities of 49 and 7kW/kg, respectively. [Copyright &y& Elsevier]

Vanadium Nitride (VN) is attractive for energy storage due to its high conductivity (1.6 × 106 S/m) and specific capacitance (1350 F/g) but limited to alkaline electrolytes for redox. In contrast, V 2 O 3 is redox active but not very conductive. In these hybrids a mixture of VN and vanadium oxide (V 2 O 3) were encapsulated in electrospun carbon-nanofibers. A combination of VN and V 2 O 3 takes advantage of the high conductivity from VN and the redox activity from V 2 O 3. Additionally, having the vanadium encapsulated within the carbon can help with the stability as the electrolyte will not have direct interaction with the surface. These hybrids were made by in-situ nitridation of the encapsulated V 2 O 5 followed by ex-situ activation with carbon dioxide. The hybrids were characterized by XPS and Raman spectroscopy. Hybrids of VN/V 2 O 3 -CNF showed increased capacitance of 245 Fg−1 with energy and power densities of 70.2 Wh kg−1 and 1751 W kg−1 in ionic liquid electrolyte. The devices showed good cycle stability with ∼90 % retention after 10,000 cycles at a current density of 1 Ag−1. These findings highlight the potential of VN/V 2 O 3 -CNF hybrids as high-performance supercapacitor electrodes. The combination of high conductivity and redox activity, along with encapsulation within CNFs, opens promising avenues for advanced energy storage. [ABSTRACT FROM AUTHOR]

Abstract: Polyacrylonitrile/poly(methyl methacrylate) (PMMA) fibers containing graphene are prepared by the electrospinning method, and hierarchical porous carbon nanofibers (CNFs) are obtained after subsequent heat treatment. The hierarchical porous CNFs have an improved structure and properties because of the increased surface area, unique nanotexture and increased electrical conductivity due to the dispersion of graphene. The carbonized fiber exhibits a high surface area (over 500m2 g−1) as result of the narrow ultramicro- and mesopore size distributions (centered at approximately 0.7 and 3.7nm, respectively), and a broad mesopore size distribution ranging from 10 to 50nm. The hierarchical pore structures are introduced by the evolution of small gas molecules during the decomposition of the PMMA during heat treatment. The highest specific capacitance of the CNFs is 128Fg−1, and the energy densities are 16.0–21.4Whkg−1 in an aqueous solution and 75.0–58.2Whkg−1 in an organic electrolyte over a power density range of 400–20,000Wkg−1. Under constant current charging/discharging at 1mAcm−2 for 100 cycles, the stability of the CNFs in a 6M KOH aqueous electrolyte decreases by ∼17% compared with the initial specific capacitance value. [Copyright &y& Elsevier]

Abstract: Carbon nanofibers were prepared using electrospinning and thermal treatment of a new precursor, poly(acrylonitrile-co-vinylimidazole). Raman spectroscopy confirmed carbonization. Steam activation resulted in high surface area of 1120m2/g. Coin cells were assembled using ethylmethylimidazolium bis(trifluoromethylsulfonyl) imide (EMITFSI) as the electrolyte. Cyclic voltammetry showed classic box-like behavior of electrochemical double layer capacitors with specific capacitances ranging between 122F/g (10mV/s) and 86F/g (300mV/s). From Ragone plots, the maximum energy and power densities were 47.4Wh/kg (0.5 A/g) and 7.2kW/kg (5 A/g), respectively. [Copyright &y& Elsevier]