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The electrospun carbon nanofibers (ECNFs) with the advantages of facile preparation method, excellent electrical conductivity and ease compounding are expected to be excellent electrode materials for supercapacitors. However, the tiny specific surface area and low specific capacitance prevent the further development of carbon nanofibers. In this work, the porous coal-based carbon nanofibers (PCCNFs-2) are fabricated via a facile dual-template method, which can be directly employed as a flexible electrode material for supercapacitors without the addition of any conductive agents and binders. As a result, the flexible self-supporting electrode (PCCNFs-2) achieves a specific capacitance of 262.0 F g−1 at a current density of 1 A g−1, excellent rate performance (81.0 % capacitance retention at a current density of 20 A g−1) and excellent cycling stability (after 10,000 cycles, 124 % capacity retention at 2 A g−1). Furthermore, the aqueous symmetrical supercapacitors (SCs) assembled with melamine foam as the storage electrolyte at an operating voltage of 1.2 V achieved an energy density of 18.5 Wh kg−1 at a power density of 150.5 W kg−1. The effective construction of this porous carbon nanofiber assures the structural integrity and achieves excellent electrochemical performance of the electrode material, which develops a new strategy for efficient utilization of porous coal-based carbon nanofibers in supercapacitors. [Display omitted] • Flexible self-supporting PCCNFs-2 electrodes were prepared via dual-template strategy. • PCCNFs-2 electrode has a capacity retention rate of 124 % after 10,000 cycles. • The symmetrical supercapacitors with PCCNFs-2 exhibits high energy density and long cycling lifespan. [ABSTRACT FROM AUTHOR]

• Co-MOF structures were anchored on the flexible MX-CNF. • Co-PC@MX-CNF and MnO 2 @Co 3 O 4 -PC@MX-CNF electrodes were derived from Co-MOF@MX-CNF. • A flexible and wearable hybrid supercapacitor was assembled using these electrodes. • The device shows an energy density of 72.5 Wh kg−1 at 832.4 W kg−1. Freestanding and flexible electrodes are crucial for advancing flexible and wearable energy storage devices (FW-ESD). However, the significant trade-off between mechanical flexibility and electrochemical performance of electrodes limits the development of high-performance FW-ESD. Therefore, flexible and freestanding multi-component hybrid electrodes with improved electrochemical properties are in high demand. This work reports a rational design of cobalt-metal organic framework (Co-MOF) structures on a highly flexible and electroconductive MXene-carbon nanofiber mat (MX-CNF). Further, the Co-MOF@MX-CNF was used as a starting material to derive capacitive-type Co-PC@MX-CNF and battery-type MnO 2 @Co 3 O 4 -PC@MX-CNF functional multi-component electrodes for a high-performance flexible wearable hybrid supercapacitor (FW-HSC). Owing to their high specific surface area (SSA), wettability, conductivity, and abundant active sites, Co-PC@MX-CNF and MnO 2 @Co 3 O 4 -PC@MX-CNF exhibited a specific capacitance of 426.7 F g−1 and a specific capacity of 475.4 mAh g−1 at 1 A g−1, respectively, with excellent mechanical flexibility. Moreover, the two electrodes were used to fabricate an FW-HSC with an operating voltage window of 1.5 V, delivering an energy density of 72.5 Wh kg−1 at a power density of 832.4 W kg−1 with long-term stability (90.36 % capacitance retention). Furthermore, a series connection of two identical FW-HSC devices could power a digital clock and light up a green LED, demonstrating its potential as a power source for various wearable devices. [ABSTRACT FROM AUTHOR]

Helical carbon nanofibers (HCNFs) assembly structure possesses huge development prospects in sorts of applications. Here we report a facile yet versatile strategy for synthetic HCNFs assembly structures (Sn-HCNFs) from Sn-based metal-organic framework (Sn-MOF) via an ethanol flame method (EFM) in atmospheric environment. As Sn-MOF is burned in ethanol flame, HCNFs grow on the surface of Sn-MOF progressively, forming an assembly structure with SnO 2 core and HCNFs-forest shell. The process of Sn-HCNFs formation is also investigated by a series of experiments, which demonstrate that, in ethanol flame, Sn-MOF is first converted to SnO 2 , and then SnO 2 catalyzes the formation of Sn-HCNFs. Furthermore, our strategy can also be extended to the preparation of various MOFs-based HCNFs and carbon nanotubes (CNTs)/carbon nanofibers (CNFs) assembly architectures. By electrochemical tests, Sn-HCNFs as electrode materials in supercapacitors exhibit superior electrochemical performances than pure HCNFs. The supercapacitors with the Sn-HCNFs electrode can remain the energy density of 21.67 Wh kg−1 at a very high-power density of 5000 W kg−1. Our strategy provides an alternative route to acquire various HCNFs or CNTs/CNFs assembly structures conveniently and will stimulate further researches on preparation and applications of them. [Display omitted] • HCNFs assembly structure (HCAS) grows from Sn-MOF in ethanol flame facilely. • SnO 2 derived from Sn-MOF in ethanol flame acts as the catalyzer for HCAS growth. • HCAS has more excellent electrochemical performance than HCNFs in supercapacitors. • Various CNFs/CNTs assembly structures form from different MOFs in ethanol flame. [ABSTRACT FROM AUTHOR]

Tailoring the chemical structures of a precursor polymer for carbon nanofibers (CNFs) produced by thermal treatment of electrospun nanofibers was studied to prepare the electrodes for electrochemical double layer capacitors (EDLCs). To improve energy storage performance of CNF electrodes, 6FDA-durene nanofibers were crosslinked by a vapor crosslinking method, and subsequently carbonized. Chemical modification via crosslinking was confirmed by FTIR spectra while the conversion of crosslinked 6FDA-durene into carbon was done by Raman spectroscopy. Electrochemical performance of these CNF electrodes was evaluated by assembling coin cells, and the CNFs derived from crosslinked 6FDA-durene nanofibers showed higher specific capacitances, energy densities and cycling stability than those from non-crosslinked ones. It was also shown that CNFs prepared using 1 min crosslinking exhibit the highest energy storage performances, a specific capacitance of 301 F g−1 (at 10 mV s−1), and the maximum energy density of 11.1 Wh kg−1 (at 0.5 A g−1) and power density of 1.8 kW kg−1 (at 6 A g−1). Surface area and porosity of CNFs, which is critical for the performance of EDLC electrodes, were studied by nitrogen adsorption/desorption measurements, and it was clearly seen that surface crosslinking of precursor polymers improved surface properties of the resultant CNFs. [ABSTRACT FROM AUTHOR]