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Enhancing the electrochemical performance while maintaining excellent mechanical properties of carbon nanofiber-based flexible electrodes remains a significant challenge, which blocks their potential application in advanced energy storage and conversion. Herein, taking advantage of the thermal stability difference between polyacrylonitrile and polypyrrolidone, we report a simple strategy to fabricate N-doped porous carbon nanofiber membranes with inter-fiber cross-linked structures via eccentric coaxial electrospinning combined with carbonization processes. During carbonization processes, the obstacles of large contact resistance are removed and sufficient contacts among electrospun nanofibers are formed, endowing the carbon nanofiber membranes with outstanding electrical conductivity (25.4 S cm−1) and flexibility in various forms. Further, NiCo 2 O 4 nanoneedles are in-situ decorated onto the prepared carbon nanofiber membranes to construct hybrid electrodes for improving capacitance. The hybrid electrodes (NiCo 2 O 4 @NPCNFs) achieve a competitive specific capacitance (capacity) of 1474.2 F g−1 (245.4 mAh g−1) at the current density of 0.5 A g−1, as well as good rate performance (78.0% capacitance retention at a current density of 10 A g−1). In addition, the assembled asymmetric supercapacitors exhibit a high energy density of 53.0 Wh kg−1. This study paves a promising way toward carbon nanofiber-based electrodes for application in energy storage systems. [Display omitted] • According to the different thermal stabilities of the polymers, cross-linked electrospun carbon nanofibers are prepared. • Design eccentric core-shell nanofibers to facilitate the outflow of the melting core to form abundant crosslinking points. • The novel carbon nanofiber membranes render robust flexibility and high electrical conductivity. • The assembled flexible supercapacitor can supply power stably and continuously even under severe bending states. [ABSTRACT FROM AUTHOR]

The development of advanced coal-based functional nanomaterials is of great significance for clean and effective utilization of coal resources. Herein, we report novel coal-based ultra-fine carbon nanosheets (UCNSs) prepared by chemical oxidation of bituminous coal with a high yield of 40.0 wt%. UCNSs show a lamellar size of 10–20 nm, mainly composed of 63.5 at.% carbon, 5.1 at.% nitrogen, and 31.4 at.% oxygen. The structural merits of suitable size distribution, enriched functional groups, and highly conjugated core enable the UCNSs showing a tri-functional reinforcement for carbon nanofibers prepared by electrospinning and carbonization. Thanks to the strong cross-linking effect and formation of entire conductive networks, the UCNS-embedded carbon nanofiber fabrics show 32.6 and 1.5 times improved mechanical strength and electrical conductivity, respectively, than the one without UCNSs. What's more, the exposed edges of UCNSs act as active sites for ultrafast capacitive energy storage, leading to the free-standing fabric with significantly improved capacitance and rate performance (191.2 F g−1 at 1 A g−1, 113.5 F g−1 at 50 A g−1) for aqueous supercapacitors. This work may provide a new thought for high-efficient and high-value-added utilization of coal resources. Ultra-fine carbon nanosheets with a high yield of 40.0 wt% were prepared through liquid-phase oxidation of bituminous coal, showing tri-functional (mechanical/electrical/electrochemical) reinforcement for carbon nanofiber fabrics. [Display omitted] • Ultra-fine carbon nanosheets with a high yield of 40 wt% were prepared from coal. • The inlaid UCNSs show tri-functional reinforcement for carbon nanofiber fabrics. • Exposed edges enable an ultra-fast pseudocapacitive energy storage ability. [ABSTRACT FROM AUTHOR]

The logical design and engineering of bimetallic oxide nanomaterials with porous carbon materials have had a significant impact on the development of high-performance electrode materials for energy storage devices in recent years. The vertical and uniform building of porous multimetal nanomaterials on the surface of nanoscale carbon fibers is difficult but not impossible. We present a self-templated metal-organic framework (MOF)-based strategy for the synthesis and assembly of bimetallic oxides/nanoporous carbon nanostructures (Ni–Fe–O/NPC) on porous carbon nanofibers (PCNFs). The vertical alignment of Ni–Fe–O/NPC at PCNFs favors a fast redox reaction by shortening the ion/electrode diffusion path at the electrode-electrolyte interface and helps enhance the overall electrochemical performance. As a freestanding electrode for supercapacitors, it has a high specific capacitance of 1419 F g−1 at 1 A g−1 and good cycling life with capacitance retention of approximately 88.5% after 10,000 cycles. The Ni–Fe–O/NPC@PCNFs-400//Fe 2 O 3 /NPC@PCNFs asymmetric supercapacitor (ASC) achieves a high energy density of 41.3 Wh kg−1 at a power density of 892.2 W kg−1 with a long cycle of life (20,000 cycles) and a high rate capability (78.6%), indicating its potential applications. [Display omitted] • MOF-derived metallic oxides on PCNFs as free-standing electrode materials for ASC. • Tetragonal rodlike Ni–Fe–O/NPC@PCNFs is successfully grown using Ni–Fe-MOF@PCNFs. • Vertical alignment of Ni–Fe–O/NPC at PCNFs provides sufficient redox-active sites. • The assembly of Ni–Fe–O/NPC@PCNFs//Fe 2 O 3 /NPC@PCNFs as an ASC delivers high energy density. [ABSTRACT FROM AUTHOR]

Triple-layered boron-containing carbon nanofibers (CNFs) with hollow channels (PPMPB) are fabricated via step-by-step electrospinning for high-performance freestanding supercapacitors. Polyacrylonitrile (PAN)-based CNFs in the first layer are chosen as the support layer material because of their excellent chemical stability and electrospinnability. The well-developed hollow channels provided fast ion diffusion in the second layer of PAN/poly(methyl methacrylate) (PMMA)-based CNFs. The surface boron functional groups constituting the third layer contribute to the pseudo-capacitance. The symmetric supercapacitor of the PPMPB electrodes delivers a maximum specific capacitance of 180 Fg−1 at 1 mAcm−2, a high energy density of 22.38 Whkg−1 at a power density of 400 Wkg−1, and an excellent retention rate of 96% after 10,000 cycles in aqueous solution. The excellent electrochemical performance is attributed to the unique sandwich nanostructure with a three-layer structure, in which the factors representing the electrochemical properties of each layer do not interfere with each other. Therefore, a moderate amount of boron and the high surface area of the triple-layer structured PPMPB can be fully utilized as an excellent conductive network and electroactive sites, which is expected in a high-performance supercapacitor electrode. [Display omitted] • Triple-layered boron-containing CNFs were fabricated by step-by-step electrospinning. • The CNFs in the first layer provide active adsorption sites for EDLC. • Hollow core present in the interlayer serves as an excellent conductive network. • A moderate amount of boron in the third layer is utilized as the electroactive site. • Symmetric PPMPB(20) electrode showed good rate capability and long cycle life. [ABSTRACT FROM AUTHOR]

Designing SnO 2 /carbon composites is an effective strategy to improve the conductivity and buffer the volume expansion of SnO 2. However, it remains a challenge to combine SnO 2 and carbon materials tightly as a stable integration. Herein, a facile and versatile strategy of Sn/SnO 2 nanodots anchored tightly into carbon nanofibers (CNFs) with the decoration of graphene quantum dots (GQDs) for high performance supercapacitor is reported. Through a simple electrospinning and carbonization reduction process, a novel multidimensional carbon skeleton of GQD/CNF effectively improves the conductivity, and importantly, abundant Sn–O–C covalent bonds are constructed to anchor SnO 2 nanodots tightly into GQD/CNF, suppressing SnO 2 aggregation and facilitating electron/ion transfer kinetics. Consequently, as self-supporting and binder-free electrode material, Sn/SnO 2 /GQD/CNF displays high specific capacitance of 168.6 mA h g−1 (1349 F g−1) at 1 A g−1 with excellent rate capability (88.9% retention at 20 A g−1). Furthermore, a flexible solid-state asymmetric supercapacitor based on Sn/SnO 2 /GQD/CNF and GQD/CNF achieves a high energy density of 32.3 W h kg−1 at a power density of 800 W kg−1 with remarkable flexibility and cycling stability (86.1% retention after 5000 cycles). The excellent electrochemical performances demonstrate that this novel carbon skeleton anchored active materials shows great potential for electrochemical energy storage applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Developing high-performing and scalable electrode materials for supercapacitors and batteries has been of tremendous interest for the world's forthcoming clean and renewable energy transition. As a versatile material, Two-dimensional graphitic carbon nitride (g-CN) has been utilized in electrochemical energy storage (EES) applications due to its nitrogen-rich adsorption sites, cost-effective production, and tunable electronic structure. The electrochemical performance of pristine g-CN has been boosted by forming hybrid architectures with highly conductive carbon-based materials, such as graphene, reduced graphene oxide, carbon nanofibers, carbon nanotubes, and beyond (e.g., MXene). Using such heterogeneous compositions for EES applications has significantly increased in recent years. This study reviews the g-CN/carbon nanomaterial (CNM) hybrids, considering the dimensionality in nanomaterials, and underscores the influence of the material's dimensionality and the synthesis/fabrication routes. The effect of structural and physicochemical changes on the electrode's electrochemical performance after hybridization is presented comparatively. Besides, the comprehensive review outlines challenges and future improvements in g-CN/CNM hybrid materials for outstanding developments in energy storage systems. [Display omitted] • Graphitic carbon nitride (g-CN)/carbon nanomaterial (CNM) hybrids are reviewed for supercapacitor and battery applications. • The impact of the CNM-type on the hybrid electrode's performance is examined through a chemical and physical perspective. • An overview of how hybrid electrode synthesis affects ion/electron transport, surface area, and porosity is provided. • Design-oriented control of the physicochemical properties for enhanced electrochemical performance is exemplified. • g-CN/CNM nanoarchitectures are emphasized as electrode materials with the potential for easy scalability. [ABSTRACT FROM AUTHOR]

Prussian blue analogs, as a pseudo-capacitor electrode materials hold great potential due to their unique framework structure, excellent electrochemical activity and high specific capacity. Herein, a versatile method for the growth of series of metal hexacyanoferrates (MHCF) on carbon nanofiber with high conductivity and flexibility was proposed. By controlling the releasing rate of metal ions through acid modulation of solution, the series of MHCF nanocubes were successfully embedded on the carbon nanofibers with super stability. Different MHCF presented various loading density. Among the MHCFs, nickel hexacyanoferrate (NiHCF) is the most easily formed with high density and uniform distribution. The obtained self-supporting NiHCF@CNF, as a representative electrode, exhibited high specific capacitance (507 F g−1, 1 A g−1) and remarkable rate performance (67% retention at 10 A g−1). Moreover, the NiHCF@CNF-based hybrid supercapacitor cell delivered a high energy density of 60 Wh kg−1 at the power density of 810 W kg−1. Meanwhile, the capacitor showed extremely high stability due to tight anchoring of NiHCF on CNFs. This work provides a simple and versatile method to produce self-supporting MHCF@CNF composites for constructing high performance supercapacitor. [Display omitted] • A versatile method to produce various MHCF@CNF is demonstrated. • The self-supporting MHCF@CNF are extremely stable with excellent flexibility. • The MHCFs particles with small size and uniform distribution promote the charge transfer. • A super high specific capacitance of 507 F g−1 (1 A g−1) is achieved on NiHCF@CNF. • NiHCF@CNF//PCNF delivers energy density of 60 Wh kg−1 at a power density of 810 W kg−1 [ABSTRACT FROM AUTHOR]

This work demonstrates hierarchical 3D nitrogen-doped carbon nanotube-carbon fibre (N-CNT@CF) networks obtained via a two-step synthetic technique: electrospinning and chemical vapour deposition (CVD) methods. Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM) reveal randomly entangled networks structure. Raman spectroscopy show structural defects, X-ray Diffraction spectroscopy (XRD) confirm the purity of the materials, while BET analysis show increase in surface area after nitrogen doping. Electrochemistry reveals that nitrogen-doping transforms surface-confined to diffusion-confined energy-storage mechanism (i.e., high power) even at low cycling rate, significantly increasing the specific capacitance of the symmetric device (155 F/g), specific energy (5.5 Whkg−1), specific power (254 W kg−1) and capacitance retention of 93% even after 10,000 cycles at 10 Ag−1. The N-CNT@CF-based symmetric cell exhibits higher f o value (ca. 82 Hz, response time, τ , of 12 ms) than the CNT@CF-based cell (ca. 25.1 Hz, 40 ms). The excellent performance of N-CNT@CF hybrid material is attributed to the Faradaic charge contribution arising from synergistic interaction between the nitrogen-doped carbon nanotubes and carbon nanofibers, high conductivity, high surface area coupled with enough accessible active sites for electrochemical reactions. This work underscores the importance of defect engineering and decoration of the vacant sites by nitrogen for enhanced supercapacitance. Image 1 [ABSTRACT FROM AUTHOR]

The aim of this study is to develop the templateless fabrication of hierarchical porous carbon nanofiber (CNF)/MnO 2 composites (PMnCD) derived from polyacrylonitrile (PAN)/cyclodextrin (CD) and investigate their morphological and electrochemical properties to determine the different capabilities of inclusion complexes (ICs) formed by α-CD, β-CD and γ-CD. Among the three CD phases, the PMnCD(β) composite using β-CD exhibits a hierarchical porous structure with large specific surface area of 499 m2g-1, and total pore volume of 0.32 cm3g-1, which helps with adsorption efficiency and accumulation of hydrated molecules for double-layer formation. In addition, the numerous mesopores and nitrogen functionalities of the PMnCD(β) composite provide fast diffusion channels for electrolyte ions and higher attractive interactions with electrolyte ions through the pseudocapacitive character. As a result, the PMnCD(β) electrode has a high specific capacitance of 228 Fg-1 at 1 mAcm−2, maximum energy density of 25.3–16.0 Whkg−1 in the power density range of 400-10,000 Wkg-1, and excellent cycling stability of more than 94% after 10000 cycles in aqueous solution, thereby offering potential applications for supercapacitors. Image 1 • Hierarchical porous PMnCD is fabricated by electrospinning without a template. • β-CD stabilizes and encapsulates MnCl 2 through the good size match of β-CD and MnCl 2. • PMnCD(β) shows a large specific surface area for accumulation of ions. • Many mesopores and nitrogen groups of PMnCD(β) provide fast ion diffusion. • Hierarchical porous PMnCD(β) is applied to high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

The preparation of electrode materials with superior electrochemical performance and excellent mechanical properties are essential for the fabrication of flexible supercapacitors. However, the compatibility of the porosity and flexibility for the electrode materials remains challenging. Herein, free-standing porous coaxial carbon nanofiber (PCCNF) membranes with large specific surface area (648 m2 g−1) and suitable pore size distribution were fabricated by a facile coaxial electrospinning technique and template method. PCCNF possesses superb capacitance of 261 and 48 F g−1 (1 A g−1) in three-electrode and two-electrode system, respectively, result in remarkable energy density (48.6 ± 3 Wh kg−1) and power density (67.5 ± 1 Wh kg−1). Moreover, supercapacitor devices based on PCCNF show superb flexibility as well as excellent electrochemical and mechanical stability. PCCNF-based high performance supercapacitors may be suitable for flexible electronic energy storage devices. Porous coaxial carbon nanofibers (PCCNF) with large specific surface area, well-balanced pore size distribution, and remarkable flexibility are fabricated by a facile coaxial electrospinning technique and template method. Flexible supercapacitors fabricated with the as-prepared PCCNF display superb electrochemical and mechanical stability. This work provides exciting opportunities for the preparation and application of flexible energy storage devices. Image 1 [ABSTRACT FROM AUTHOR]

Flexible supercapacitors have drawn tremendous attention resulting from the rapid development of wearable electronic devices. Herein, we develop an effective and facile two-step approach to prepare high content nitrogen, sulfur co-doped porous carbon nanofibers film as electrodes of flexible supercapacitors. Benefiting from the high specific surface area and rich nitrogen/sulfur content, nitrogen and sulfur co-doped porous carbon fibers film (N, S co-doped PCFF) electrodes exhibit a high mass specific capacitance of 307.8 F g−1, and the capacitance retains 98% of initial capacitance after 5000 cycles in a three-electrode system. The as-assembled flexible supercapacitor devices with polyvinyl alcohol/KOH gel electrolyte demonstrate a highest mass specific capacitance of single electrode of 183.9 F g-1 at the scan rate of 2 mV s-1, which is better than that of other heteroatom doping carbon materials. In addition, the energy density reaches as high as 16.35 Wh kg−1 with the power density of 147 W kg−1 and retains as 5.34 Wh kg−1 with higher power density of 2402 W kg−1. Furthermore, the flexible devices show good cycling stability, superior flexibility and stable electrochemical performance. Schematic demonstration of Nitrogen, Sulfur co-doped PCFF electrodes, and schematic structure of flexible all-solid-state supercapacitor. Image 1 [ABSTRACT FROM AUTHOR]

Translating the advantages of carbon nanomaterials into macroscopic energy storage devices is challenging because the desirable nanoscale properties often disappear during assembly processes. Here we describe a new nonequilibrium subcritical hydrothermal method capable of independently manipulating the temperature and pressure to create unique assembly conditions crossing the commonly used liquid-vapor boundary. Highly conductive and dense-packed yet ion-accessible nanocarbon microfibers can be obtained from graphene oxide sheets, single-walled carbon nanotubes, and a nitrogen-doping crosslinker under 20 min of hydrothermal assembly, 80% energy saving compared to standard hydrothermal methods, and one of the shortest time in the field of hydrothermal processing of carbon nanomaterials. Using those microfibers, we built microsupercapacitors that reach a high volumetric capacitance of 52 F cm −3 , energy density of 7.1 mWh cm −3 , and power density of 1645.7 mW cm −3 , respectively. We further demonstrate the 3D integration of multiple fiber microsupercapacitors that reduces the device footprint by 75% while expanding the operational voltage and current window. This strategy is a promising tool for harmoniously assembling carbon nanostructures as energy storage components for various energy applications. [ABSTRACT FROM AUTHOR]

Vanadium pentoxide (V 2 O 5 ) has attracted much attention for the promising electrode material of supercapacitor because of its high Faradaic activity and stable crystal structure but suffer from the low electronic conductivity and poor ionic diffusivity. Previous methods improve performance via attachment of nanoscale V 2 O 5 onto the carbon host with oxygen-containing functional group, which may decrease the intrinsic electrical conductivity of carbon and lead to poor behavior of electronic transport process. Herein we report a new strategy for the preparation of 3D monolithic porous aerogels consisting of uniform carbon nanofibers (CNFs)/V 2 O 5 core/shell nanostructures by introduction of nitrogen atoms into CNFs lattice structure. As a proof-of-concept we have combined simulations and experiments analysis to demonstrate the effect of N doping treatment on the formation of CNFs/V 2 O 5 core/shell nanostructures. Benefiting from the stable and homogeneous core/shell morphology, the improved charge-transfer effect of CNFs, 3D N-doped CNFs (N-CNFs)/V 2 O 5 composite aerogel exhibits high specific capacitance (595.1 F g −1 ), excellent energy density (82.65 W h Kg −1 ), and extremely outstanding cycling behavior (>12000). The approach of introducing N atoms into carbon lattice may be leveraged to a wide range of carbon materials for fabricating metal oxide/carbon composite nanomaterial, leading to opening up new opportunities for these electrode materials in high-energy-density storage systems. [ABSTRACT FROM AUTHOR]

Porous and interconnected electrodes based on carbon nanoarchitectures offer comprehensive advantages of large specific surface area and high porosity consequently increasing the specific capacitance of ultracapacitor energy storage systems. Emulsion-templated polymers, PolyHIPEs (Polymerized High Internal Phase Emulsions) are highly porous polymers with a structure of cages interconnected by windows thus provide suitable framework to create such porous carbon nanostructures. Herein, nitrogen enriched porous carbon nanosheets are synthesized by pyrolysis of polymer-silica hybrid PolyHIPE and subsequent silica removal. This nitrogen enriched porous carbon nanosheets when tested as an electrode for ultracapacitor, showed specific capacitance as high as 209 F/g at a current density of 1 A/g in 1 M H 2 SO 4 with excellent capacity retention over long cycling. [ABSTRACT FROM AUTHOR]

It is demonstrated that the performances of supercapacitors are often affected by the electrochemical interface in their electrodes. In this work, the electrochemical interface in carbon nanofiber (CNF)/carbon nanotube (CNT) hierarchical composites was well optimized by tuning the diameters of electrospun CNF skeletons and the densities/lengths of CNT hierarchies. The optimized CNF/CNT composites decorated with MnO 2 exhibited high specific capacitance (∼631.0 F g −1 at current density of 0.9 A g −1 ) and excellent cycling stability (over 95% after 1500 cycles). Moreover, the assembled symmetric supercapacitors show a high flexibility and an excellent dynamic cycling stability, outputting the maximum energy density of 19.11 W h kg −1 and the maximum power density reaching 25,000 W kg −1 . This research confirmed that the performances of the electrodes based on CNF/CNT hierarchical composites and their counterpart devices can be well tuned by tailoring their three-dimensional electrochemical interface. [ABSTRACT FROM AUTHOR]

The mesoporous carbon nanofibers (MCFs) with large cage-like pores have been fabricated by thermally treating electrospun fibers of polyvinyl alcohol containing tin compound. During the process, tin oxide is reduced to melting tin and the carbon is activated to form the porous carbon. The results of X-ray diffraction and transmission electron microscopy at different temperatures show that particles of SnO2 (∼1.9nm) exist in the fibers at 300°C while mixtures of Sn and SnO with rod-like shapes appear in the matrix when the fibers are heated at 400°C, and that Sn migrates to the surface of fibers and pores are formed in the fibers at higher temperature. Specific surface area of MCFs can reach 800m2 g−1 and the average diameter of interior pores is about 10.3nm while the entrance pores are small. The specific capacitance of MCFs is 105Fg−1 and the fabricated symmetrical capacitors exhibit high-rate capacitive properties and excellent stability, Pt nanoparticles which can be densely loaded on MCFs exhibit relatively high activity and stability toward electro-oxidation of methanol, which indicate that MCFs may be used as electrodes for high-rate energy storage and support for catalyst. This approach may be extended to prepare other porous carbon materials. [ABSTRACT FROM AUTHOR]

Abstract: An asymmetric supercapacitor with high energy and power densities has been fabricated using MnO2/carbon nanofiber composites as positive electrode and activated carbon nanofibers as negative electrode in Na2SO4 aqueous electrolyte. Both electrode materials are freestanding in nature without any conductive additives or binders and exhibit outstanding electrochemical performances. The as-assembled asymmetric supercapacitor with optimal mass ratio can be operated reversibly over a wide voltage range of 0–2.0V, and presents a maximum energy density of 30.6Whkg−1, which is much higher than those of symmetric supercapacitors. Moreover, the supercapacitor exhibits excellent rate capability (high power density of 20.8kWkg−1 at 8.7Whkg−1) and long-term cycling stability with only 6% loss of its initial capacitance after 5000 cycles. These attractive results make these freestanding materials promising for applications in aqueous electrolyte-based asymmetric supercapacitors with high energy and power densities delivery. [Copyright &y& Elsevier]

Abstract: Microporous carbon nanofibers were prepared by electrospinning from resole-type phenolic resin, followed by one-step activation. KOH was utilized to tune the fiber diameter and improve porous texture. By adjusting KOH content in the spinning solution, the fiber diameter could be controlled in the range of 252–666nm and the microporous volume and specific surface area could be greatly improved. The electrochemical measurements in 6M KOH aqueous solution showed that the microporous carbon nanofibers possessed high specific capacitance, considerable rate performance, and superior specific surface capacitance to conventional microporous carbons. The maximal specific capacitance of 256Fg−1 and high specific surface capacitance of 0.51Fm−2 were achieved at 0.2Ag−1. Furthermore, the specific capacitance could still remain 170Fg−1 at 20Ag−1 with the retention of 67%. Analysis showed that the high specific surface capacitance of the resultant carbons was mainly attributed to optimized pore size (0.7–1.2nm) and the excellent rate performance should be principally due to the reduced ion transportation distance derived from the nanometer-scaled fibers. [Copyright &y& Elsevier]