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MXene-integrated N-doped cavity-interconnected porous carbon nanofibers flexible film with excellent energy storage performance was prepared by a non-pre-oxidation synthesis strategy combining electrospinning and metal–organic framework derivatization. [Display omitted] • The flexible carbon film is constructed by MXene-integrated N-doped cavity-interconnected porous carbon nanofibers. • The non-preoxidation synthesis strategy overcomes the MXene oxidation and active site loss caused by the flexible carbon film during the preparation process. • The flexible carbon film exhibits a high energy density of 26.2 Wh kg−1 at 500 W kg−1 and good capacitance retention (96.3 %) after 10,000 charge–discharge cycles. • This study develops an effective general strategy for the preparation of embedded carbon nanofiber flexible film. Although the flexible carbon film integrated with MXene has been proven to be a new generation of supercapacitor material with good energy storage prospects, the MXene oxidation and the lack of active sites during the preparation of the carbon film can lead to irreversible capacity loss. Herein, a flexible carbon film constructed by MXene-integrated N-doped cavity-interconnected porous carbon nanofibers was prepared by a non-pre-oxidation synthesis strategy combining electrospinning and metal–organic framework derivatization. This flexible carbon film overcomes the oxidation problem of MXene during the stabilization of polyacrylonitrile, and the derived porous structure of cavity interconnection exposes more active sites. Due to its unique structural characteristics and ideal chemical composition, this independent flexible carbon film exhibits significantly enhanced electrochemical performance as an electrode material for supercapacitors. It exhibits an energy density of 26.2 Wh kg−1 at a power density of 500 W kg−1, and a capacitance retention rate of 96.3 % after 10,000 charge–discharge cycles. This study provides a unique strategy for the preparation of high-performance flexible carbon films, and this technology can also be extended to other integrated CNF composites for the design of high-performance supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

In view of the problems surrounding the research and application of carbon materials, the process of choosing a carbon source is still not perfect. There are few studies concentrating on the establishment of structure–property relationships based on the choice of carbon source. In this regard, our present work contributes the design of an organic precursor that is expected to allow the controllable construction of the carbon material, thus regulating its functionality. A highly π-conjugated Schiff base moiety with alternating imine groups (C＝N) and benzene rings was incorporated into the main chain of a mesoporous polymer. For comparison, a bisphenol-A-type moiety was employed in the main chain of another mesoporous polymer. Using the mesoporous polymers as organic precursors for porous carbon sources, the formation of mesoporous carbon can be attributed to the presence of the highly π-conjugated Schiff base moiety due to its self-supporting effect and char-forming ability, which are absent in the bisphenol-A-type moiety. However, we are not only concerned with the contribution from the chemical structure of the designed precursor to the controllable construction of mesoporous carbon, but also concerned with its regulation of the electrochemical performance of the resulting material. Through characterization using cyclic voltammetry (CV), galvanostatic charge–discharge profiles, and electrochemical impedance spectroscopy (EIS), this kind of mesoporous carbon has been found to have excellent charge storage and transportation abilities and shows potential for application in the electrodes of electrochemical capacitors. [ABSTRACT FROM AUTHOR]

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]

The thriving energy demand of the gradually increasing population and modernised life style requires development in energy storage devices for usage in commercial electronic devices. In this particular work, we have explored electrochemical performances of bimetallic oxide Ag 2 WO 4 nanorods and tuned its performance by decorating it on the nitrogen doped carbon nanofiber (N-CNF). The Ag 2 WO 4 nanorods are synthesised by a facile route of co-precipitation method followed by ultrasonication with N-CNF. The synthesised Ag 2 WO 4 nanorods was found electrochemically active and the incorporation of N-CNF end up boosting its electrochemical performances. The obtained nanocomposites were characterised by various advanced techniques. The amount of N-CNF was determined by characterisation via the potentiostatic and galvanostatic cycle measurements and electrochemical impedance spectroscopy (EIS). The electrochemically active Ag 2 WO 4 with 20 wt% of N-CNF (Ag 2 WO 4 /N-CNF b) exhibited 2.2-fold higher charge storage capacity than pristine Ag 2 WO 4. The Ag 2 WO 4 /N-CNF b exhibited specific capacitance as high as 330 F g−1 at a constant applied current density of 1 A g−1 in 1 M KOH. The improved capacity may be due to conductive pathways provided by N-CNF. The Ag 2 WO 4 got well decorated over the N-CNF facilitating the active sites interaction with electrolyte. The symmetric device fabricated with Ag 2 WO 4 /N-CNF b electrodes exhibited excellent energy density of 10 W h kg−1 at 6000 W kg−1 at 5 A g−1. The Ag 2 WO 4 /N-CNF b electrode long-term stability has been minutely observed; the high Coulombic efficiency of 90% and high rate of capacity retention 98% even after 3000 cycles. Owing to these excellent electrochemical properties, the research work can potentially widen the opportunity to explore other profound bimetallic oxides and its nanocomposites with conductive carbon-based matrix for energy storage applications. [Display omitted] • Ag 2 WO 4 nanorods, easily synthesised by co-precipitation method is found to be electrochemically active in 1 M KOH. • Decorating Ag 2 WO 4 on N-doped CNF boost electrochemical charge storage owing to high active sites and improved conductivity. • The Ag 2 WO 4 @N-CNF nanocomposite electrode has been used further to develop electrochemical symmetric supercapacitors. • Such work open door for exploring other bimetal oxides and carbon composites and synergistic effect for various applications. [ABSTRACT FROM AUTHOR]

A series of highly homogeneous polyaniline@N/P co-doped carbon nanofibers (PANI@NPCNFs) composites have been prepared by in-situ polymerization of aniline on the surface of NPCNFs. Vertically oriented PANI nanothorns are achieved by introducing phosphorus groups on the surface of NPCNFs. The optimized PANI@NPCNFs composite demonstrates outstanding electrochemical performance with high specific capacitance (436 F g −1 at 0.5 A g −1 ), high rate capability (79% capacitance retention at 20 A g −1 relative to that at 0.5 A g −1 ), and good stability (96% capacitance retention after 1000 cycles at 10 A g −1 ). The excellent electrochemical performance can be attributed to the surface phosphorus-oxygen groups which bridge the gaps between PANI and NPCNFs, leading to highly enhanced charge transfer dynamics. [ABSTRACT FROM AUTHOR]

Heteroatom-doped mesoporous carbon nanofibers (HMCNFs) were prepared by direct carbonization of highly cross-linked organic–inorganic hybrid polymeric nanofibers (PNFs) under an inert atmosphere. The HMCNFs were of large Brunauer–Emmett–Teller (BET) surface area, uniform mesopore (with diameter 4 nm), and high content of heteroatoms. Electrodes prepared by using HMCNFs showed a high specific capacitance of 214.9 F/g in 6 M KOH electrolyte, because of the large BET surface area and high content of heteroatoms. This work involved preparation of carbon nanofibers from a novel precursor and used the nanofibers in the fabrication of high-performance supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Pyrite iron sulfide (FeS 2) is a fascinating electrode material for energy reserve devices because of its high theoretical capacity, non-polluting nature and abundant resources. However, the practical application has been extremely inhibited owing to its poor rate capacity and short cyclability caused by volume change during charge/discharge processes. In this article, a novel nanocomposite that is hollow FeS 2 nanospheres encapsulated in N/S co-doped carbon nanofibers (FeS 2 CNFs) was synthesized through electrostatic spinning. The FeS 2 CNFs nanocomposite demonstrates a terrific specific capacity of 511 F g−1 at 1 A g−1 for all-solid-state supercapacitors. The FeS 2 CNFs as electrode material for sodium-ion batteries (SIB) displays a specific capacity of 827.7 mAh g−1 and possesses a capacity of 490.6 mAh g−1 at 0.05 A g−1 after 200 cycles. The results indicate that this encapsulated structure can guarantee the integrity of electrode materials. And the abundant defects in carbon nanofibers caused by N/S co-doping may increase electrochemical reaction sites to facilitate charge transfer. The N/S co-doped FeS 2 CNFs nanocomposite exhibits a great potential for applying in SIB and supercapacitors. • Hollow FeS 2 nanospheres are encapsulated in carbon nanofibers by electrostatic spinning. • In-situ S-doping can increase the electrochemical active sites. • The incorporation of carbon nanofibers can prevent the structure collapse of FeS 2. [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]

High intrinsic ionic conductivity and a theoretical capacity of MoS 2 is well appreciated and gathered great attention for an electrode asset for energy storage applications. The MoS 2 layers inter connected with one-dimensional carbon nanofibers (CNFs) are successfully prepared to give a conductive three-dimensional network for the robust charge transfer kinetics. The MoS 2 nanosheets adhered together to form micro flowers accomplished by a simple hydrothermal process. Further, the nanosheets are allowed to grow over the electrospun CNFs directly. The structural, functional, and morphological characterizations unanimously revealed the nanocomposite formation. Also, the surface area has been determined by BET analysis and subjected to electrochemical studies as an electrode for supercapacitors. The nanocomposite deposited on the graphite sheet (1 × 1 cm2) displays the high capacitance counterparts of 903.9 Fg-1 achieved by a lower current density of 1 Ag-1 and maintained 94% efficiency even 5000 cycles after a charge-discharge process. This process was examined with the potential range of 0.8 V (−0.4 to +0.4 V) in 1 M KCl electrolyte. These results confirms the prepared nanocomposite can be used as a proficient electrode for the creation of high capacitance supercapacitors with good cyclability. Image 1 • Direct growth of MoS 2 on carbon nanofibers attained by facile hydrothermal process. • FESEM and XRD results confirms the MoS 2 encapsulated CNFs with hexagonal phase. • CV were employed with different electrolytes to evaluate the influence of ion size. • The prepared MoS 2 /CNF exhibits the specific capacitance of 903.9 Fg-1 at a current density 1 Ag-1. • It maintains 94% efficiency even after 5000 cycles. [ABSTRACT FROM AUTHOR]

Porous carbon nanofibers (CNFs) with high energy storage performance were fabricated with a single precursor polymer, 6FDA-TFMB, without the use of any pore-generating materials. 6FDA-TFMB was synthesized, electrospun, and thermally treated to produce binder-free CNF electrodes for electrochemical double-layer capacitors (EDLCs). Highly porous CNFs with a surface area of 2213 m2 g−1 were prepared by steam-activation. CNFs derived from 6FDA-TFMB showed rectangular cyclic voltammograms with a specific capacitance of 292.3 F g−1 at 10 mV s−1. It was also seen that CNFs exhibit a maximum energy density of 13.1 Wh kg−1 at 0.5 A g−1 and power density of 1.7 kW kg−1 at 5 A g−1, which is significantly higher than those from the common precursor polymer, polyacrylonitrile (PAN). [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]

Electrochemical capacitors (ECs) can provide ultra-long cycle life and ultra-fast energy delivery, characteristics which most battery technologies lack. Making composites out of carbon and pseudocapacitive materials is a popular strategy directed on narrowing the gap in energy density with regard to batteries. Usually, the incorporation of pseudocapacitive materials leads to a decrease in power performance compared to a pure carbon matrix, due to inferior electrical conductivity. This work, however, presents significant improvement in rate capability demonstrated by a composite electrode containing carbon nanofibers (NCNF) and manganese oxides (MnO 2). The NCNF/MnO 2 is prepared with a common method through the reaction with permanganate. The material has excellent performance metrics, especially a 78.2% rate capability (capacitance retention at 15 A g−1 relative to 0.5 A g−1), more than 10 times that for the NCNF carbon matrix. The exceptional enhancement can be explained by the development of micropores and surface area of NCNF, thus alleviating the "pore starvation" issue, and surface functional groups variation that enhances capacitive performance. This work highlights the importance of paying attention to the modification of carbon substrate when investigating carbon composite electrodes e.g. carbon/MnO 2 networks. • N-doped carbon nanofiber (NCNF) electrodes were derived from cellulose. • Compositing NCNF with MnO 2 led to surprising enhancement in rate capability. • 88.8 F g−1 capacitance was obtained at 15 A g−1 for the composite electrode. • Porosity and surface chemistry of NCNF were improved during compositing. [ABSTRACT FROM AUTHOR]