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We developeda facile method to construct flexible, freestanding three dimensional hierarchical electrodes that consist of graphene encapsulated one-dimensional conducting polyaniline (PANi)@MnO2 coaxial nanowires grown on electrospun carbon nanofibers (denoted as G-PANi@MnO2/ECNFs). A combination of XRD, SEM, and TEM techniques were used to characterize the structures of G‑PANi@MnO2/ECNFs. Electrochemical measurements confirmed that such nanostructured composites possessed higher electrochemical capacitance than that of each individual component due to synergistic effects. The G-PANi@MnO2/ECNFs electrode exhibited extremely high specific capacitance (1364.3 F/g at 0.3 A/g) and superior cycling stability (89.2% retention rate after 2000 cycles) in a 1 M Na2SO4 aqueous solution. The excellent electrochemical performance of such nanoscale architectured electrodes provides a new route to develop flexible, freestanding, and high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

In this study, an electrospinning method was used to produce highly conductive freestanding carbon nanofibers (CNFs). The freestanding CNFs are compatible with hierarchical growth techniques, such as hydrothermal processes, for the nanostructure engineering of supercapacitor electrodes with enhanced electrochemically active sites. Therefore, the flower-like FeMoO 4 @CNF nanosheets were investigated to improve the electrochemical performance using aqueous and neutral electrolytes (Na 2 SO 4 and K 2 SO 4). The optimized FeMoO 4 @CNF electrode exhibits areal capacitances of 252 and 220 mF·cm−2 at a high current density of 2.5 mA·cm−2 with Na 2 SO 4 and K 2 SO 4 electrolytes, respectively. The wide potential window (1.6 V) of the symmetric supercapacitor delivered maximum energy densities of 22.4 and 19.6 μWh·cm−2 at a power density of 2 mW·cm−2 for Na 2 SO 4 and K 2 SO 4 electrolytes, respectively. [ABSTRACT FROM AUTHOR]

Exploring anode materials with an excellent electrochemical performance is of great significance for supercapacitor applications. In this work, a N-doped-carbon-nanofiber (NCNF)-supported Fe3C/Fe2O3 nanoparticle (NCFCO) composite was synthesized via the facile carbonizing and subsequent annealing of electrospinning nanofibers containing an Fe source. In the hybrid structure, the porous carbon nanofibers used as a substrate could provide fast electron and ion transport for the Faradic reactions of Fe3C/Fe2O3 during charge–discharge cycling. The as-obtained NCFCO yields a high specific capacitance of 590.1 F g−1 at 2 A g−1, superior to that of NCNF-supported Fe3C nanoparticles (NCFC, 261.7 F g−1), and NCNFs/Fe2O3 (NCFO, 398.3 F g−1). The asymmetric supercapacitor, which was assembled using the NCFCO anode and activated carbon cathode, delivered a large energy density of 14.2 Wh kg−1 at 800 W kg−1. Additionally, it demonstrated an impressive capacitance retention of 96.7%, even after 10,000 cycles. The superior electrochemical performance can be ascribed to the synergistic contributions of NCNF and Fe3C/Fe2O3. [ABSTRACT FROM AUTHOR]

Among various types of energy storage, the supercapacitor is regarded as the most promising device due to its long cycling life, good cycling stability, and high power density. A supercapacitor is generally composed of electrodes, electrolytes, and a separator. The separator is one of the most important components, serving to prevent internal short circuits between the anode and the cathode. Herein, a nanostructured-based separator in a PAN/PVDF nanofiber scheme is introduced for improving the electrochemical performance of the supercapacitor. Briefly, the membranes were produced via the electrospinning technique. All of the raw materials were blended in various compositions of PVDF for optimization purposes. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were carried out to identify the microstructure of the nanofibers. The electrochemical properties of the membrane were measured using galvanostatic charge-discharge (GCD). Based on GCD, it was shown that the PAN/PVDF 20 wt% membrane exhibited the optimum gravimetric capacitance at 54.104 Fg-1 as evidenced by a high porosity percentage. Thus, the PAN/PVDF nanofiber has good potential as a separator for application in supercapacitors. [ABSTRACT FROM AUTHOR]

A series of core-triple-shelled GCNF/PANI/NCO nanostructures have been fabricated via a facile strategy. Taking full advantage of the free-standing architecture of graphene-coated electrospun carbon nanofibers (GCNF), high conductivity and flexibility of the polyaniline (PANI) layers, and abundant active sites of nickel carbonate hydroxide (Ni 2 (CO 3)(OH) 2) nanosheets, the optimal electrode exhibits a high specific capacitance of 1565F g−1 at 1 A/g, which exceeds almost all of the reported nickel carbonate hydroxide-based electrodes in literatures. A hybrid supercapacitor delivers a high energy density of 35.4 Wh kg−1@750 W kg−1 and a long cycle lifespan. This strategy enables the controllable synthesis of core-triple-shelled hierarchical materials applicable to diverse electrochemical applications. [Display omitted] • We prepared the core-triple-shelled GCNF/PANI/NCO fiber-based films via a new route. • The optimal electrode exhibits high electrochemical properties via joint actions. • A hybrid supercapacitor displays large specific capacities and high energy density. • This strategy provides a new way to synthesize other core-triple-shelled materials. Designing novel efficient electrode materials with controlled hierarchical structure and composition for advanced supercapacitors remains a great challenge. Herein, a core-triple-shelled hierarchical GCNF/PANI/NCO nanostructure has been designed and fabricated by sequential growth of the conductive polyaniline (PANI) layers and nickel carbonate hydroxide (Ni 2 (CO 3)(OH) 2) nanosheets on the graphene-coated electrospun carbon nanofibers (GCNF) via a facile wet-chemical strategy. Taking full advantage of the free-standing architecture of graphene-coated electrospun carbon nanofibers, high conductivity and flexibility of the PANI layers, and abundant active sites of Ni 2 (CO 3)(OH) 2 nanosheets, the optimal GCNF/PANI/NCO (2 h) electrode exhibits a high specific capacitance of 1565F g−1 at 1 A/g and enhanced rate capability, which are higher than those of the GCNF, GCNF/PANI, and GCNF/NCO (2 h) electrodes at the same situation, and also exceeds most of the reported nickel carbonate hydroxide-based electrodes in literature. The superior performance should be mainly ascribed to the collaborative contribution of each component. Moreover, a self-assembled GCNF/PANI/NCO//AC hybrid supercapacitor delivers a high energy density of 35.4 Wh kg−1@750 W kg−1 and a long cycle lifespan. This strategy enables the controllable synthesis of core-triple-shelled hierarchical materials applicable to advanced electrochemical applications. [ABSTRACT FROM AUTHOR]

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 booming demand for energy storage has driven the rapid development of energy storage devices such as supercapacitors, and the research on high-performance electrode materials, a key component of supercapacitors, has gained tremendous attention. In this research, phenolic resin-based multi-porous carbon nanofibers have been prepared by electrospinning, curing, carbonization and activation and then employed as advanced electrode materials in supercapacitors. We demonstrate that the material is nano-scale continuous fiber, and its surface has pore distribution of different sizes. It delivers a high specific capacitance of 242 F g−1 at a current density of 0.2 A g−1 and maintains 148 F g−1 even at a high current density of 20 A g−1. Moreover, it shows almost no capacitance decay at a current density of 2 A g−1 over 1000 cycles, demonstrating its great potential as high-performance electrodes in supercapacitors. [ABSTRACT FROM AUTHOR]

Transition−metal−based materials show great promise for energy conversion and storage due to their excellent chemical properties, low cost, and excellent natural properties. In this paper, through simple strategies such as classical electrospinning, air calcination, and the one−step hydrothermal method, a large area of Ni(OH)2 nanosheets were grown on NiMoO4 nanofibers, forming NiMoO4@Ni(OH)2 nanofibers. The one−dimensional nanostructure was distributed with loose nanosheets, and this beneficial morphology made charge−transfer and diffusion more rapid, so the newly developed material showed good capacitance and conductivity. Under the most suitable experimental conditions, the optimal electrode exhibited the highest specific capacitance (1293 F/g at 1 A/g) and considerable rate capability (56.8% at 10 A/g) under typical test conditions. Most interestingly, the corresponding asymmetrical capacitors exhibited excellent electrochemical cycle stability, maintaining 77% of the original capacitance. NiMoO4@Ni(OH)2 nanofibers were verified to be simple to prepare and to have good performances as energy−storage devices within this experiment. [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]

Schematic illustration of the preparation of porous carbons. [Display omitted] • The porous carbons with controllable architecture were fabricated by a dual-role KCl-assisted activation method. • KCl not only serves as an auxiliary template but also contributes to an enhancement in the melting of K 2 CO 3. • The prepared porous carbons possess well-developed pore structure and excellent electrochemical performance. • This work paves a path to prepare porous carbons via an environment-friendly and cost-effective route for supercapacitors. Preparation of high-performance electrode materials in a low-cost and simple way is of great significance for the application and development of supercapacitors. Herein, a dual-role KCl-assisted KOH activation method with low KOH consumption was employed to fabricate porous carbons with controllable architecture, using the coal liquefaction residue (CLR) as the raw material. It is indicated that KCl not only serves as an auxiliary template for pore-forming but also contributes to an enhancement in the melting of K 2 CO 3 , an intermediate of KOH activation, resulting in an improvement in the efficiency of KOH activation. As a consequence, the prepared samples possess highly developed pore structure even at a low KOH consumption, which endow them with excellent capacitive performance. The as-fabricated optimal porous carbon (LR-KPC-4) displays a maximum specific capacitance of 375 F g−1 at 0.5 A/g and superior rate capacity, which are much better than those of the porous carbon prepared without KCl. The fabricated symmetric supercapacitor shows a high specific capacitance of 256 F g−1 at 0.5 A/g, energy density of 8.9 Wh kg−1 at 125 W kg−1 and great cycling stability. This work demonstrates a facile strategy to efficiently convert CLR into porous carbons for high-performance supercapacitors. Meanwhile, it paves a promising way for value-added utilization of CLR. [ABSTRACT FROM AUTHOR]

Using renewable biomass precursors to develop high-performance carbon electrodes is a promising approach for the advancement of supercapacitors. This work proposes a feasible strategy to prepare self-supporting flexible porous carbon nanofibers by electrospinning and carbonizing the mixture of cuttlefish ink, polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA). The impacts of cuttlefish ink precursor on the structure, elemental composition, and capacitance properties of carbon nanofibers have been studied. Herein, the unique structural advantage of cuttlefish ink can significantly optimize the porous structure of carbon nanofibers. Due to the hierarchical porous structure, large specific surface area, hollow channels and high nitrogen content, the carbon nanofibers offer a high specific capacitance of 364.8 F g−1 at 0.5 A g−1 current density, alongside desirable rate performance and cycle life. Furthermore, the carbon nanofiber electrode performs good mechanical flexibility. The flexible solid-state supercapacitor based on this electrode exhibits 14.1 Wh kg−1 energy density at 0.4 kW kg−1 power density, and 97.8% capacitance retention after 5000 cycles. The favorable capacitive properties make this carbon nanofiber material a potential candidate for supercapacitor electrodes. [Display omitted] • Electrospun porous carbon nanofibers (CPP–CNF) were prepared from cuttlefish ink. • CPP-CNF features hierarchical pores and hollow channels. • CPP-CNF is mechanically flexible with superior capacitive performance. • The flexible supercapacitor achieves high energy density and cycling stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Self-O-doped Alpinia galanga stem-based carbon nanofiber succesfully synthesis. • The hierarchical porous carbon exhibit high specific surface area of 1065.58 m2/g. • The porous carbon was performed in solid-free binder form. • In 2-electrode system, supercapacitor possessed specific capacitance of 226F g−1. In this study, activated carbon with hierarchical pores and a nanofiber structure doped with oxygen was prepared using a pure biomass-based sustainable strategy involving integrated chemical impregnation and pyrolysis. Alpinia galangal stem was chosen as it functions as fast conductive network with abundant electrochemical active sites for high-grade electrode materials. The optimal precursor exhibited self-doping of oxygen ranging from 6.15 to 15.69 % with 1065.58 m2/g, which contributed to the redox reaction of the electrode material. When tested in a 2-electrode system, the porous carbon nanofibers showed a high specific capacitance of 226F g−1 at 1 A g−1 in 1 M H 2 SO 4 electrolyte, producing an energy density of 9.3483 Wh kg−1 with a coulombic efficiency of 89.01 %. The results showed that oxygen-doped hierarchical porous carbon nanofibers produced from Alpinia galangal stem biomass and designed to be solid-free of binders are highly promising as high-quality electrode materials that can improve sustainable supercapacitor performance. [ABSTRACT FROM AUTHOR]

N/P dual-doped three-dimensional porous carbon was synthesized via nano-CaCO 3 template-assistant carbonization of intumescent flame retardants (IFRs) precursor. [Display omitted] Heteroatom-doped three-dimensional (3D) porous carbons possess great potential as promising electrodes for high-performance supercapacitors. Inspired by the inherent features of intumescent flame retardants (IFRs) with universal availability, rich heteroatoms and easy thermal-carbonization to form porous carbons, herein we proposed a self-assembling and template self-activation strategy to produce N/P dual-doped 3D porous carbons by nano-CaCO 3 template-assistant carbonization of IFRs. The IFRs-derived carbon exhibited large specific surface area, well-balanced hierarchical porosity, high N/P contents and interconnected 3D skeleton. Benefitting from these predominant characteristics on structure and composition, the assembled supercapacitive electrodes exhibited outstanding electrochemical performances. In three-electrode 6 M KOH system, it delivered high specific capacitances of 407 F g−1 at 0.5 A g−1, and good rate capability of 61.2% capacitance retention at 20 A g−1. In two-electrode organic EMIMBF 4 /PC system, its displayed high energy density of 62.8 Wh kg−1 at a power density of 748.4 W kg−1, meanwhile it had excellent cycling stability with 84.7% capacitance retention after 10,000 cycles. To our best knowledge, it is the first example to synthesize porous carbon from IFRs precursor. Thus, the current work paved a novel and low-cost way for the production of high-valued carbon material, and expanded its application for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Summary: The development of efficient methods to achieve a porous activated carbon nanostructures electrode for high‐performance electrochemical double‐layer capacitor (EDLC) is urgently needed at present. In this study, biomass‐based porous hollow carbon nanofiber/nanosheet with suitable micro/mesopores was successfully prepared using a low‐cost simple approach through chemical activation at direct pyrolysis. Biomass‐based porous carbon was performed in two different chemical activation of KOH and ZnCl2. The effects of the different KOH/ZnCl2 concentrations at high‐temperature pyrolysis on the morphological structure and porosity were investigated. The synthesized activated carbon possesses micro/mesopores hollow nanofiber/nanosheet, which enhanced specific surface area from 15.163 m2 g−1 to ultrahigh specific surface area of 1041.900 m2 g−1. These behaviors exhibit a high specific capacitance of 213 F g−1 in a two‐electrode system with excellent energy and power density of 29.6 Wh kg−1 and 106.6 W kg−1 at 1 M H2SO4 aqueous electrolyte. These results provided accurate information about a feasible approach to synthesize biomass‐based porous hollow carbon nanofiber/nanosheet to boost high‐performance energy storage devices. [ABSTRACT FROM AUTHOR]

The hydroxyl-functionalized poly (amic acid) (PAA) is first synthesized from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and electrospun into nanofibers. Then, the PAA nanofibers are thermally imidized at 300 °C and rearranged at 450 °C, followed by an ultimate carbonization to obtain hydroxyl-functionalized polyimide (HPI) based carbon nanofibers (CNFs). When the PAA concentration and carbonization temperature are respectively optimized as 28 % and 800 °C, the obtained CNF specimen HPI(6FAP-6FDA)-28-800 exhibits a better electrochemical performance, with a specific capacitance of 226.3 F g−1 at 0.5 A g−1. Subsequently, the HPI(6FAP-6FDA)-28-800 is subjected to KOH activation treatment. When the CNF/KOH mass ratio is 1/3, the activated sample CNF(6FAP-6FDA)-1/3 displays a maximum specific capacitance of 354.0 F g−1, coupled with a high rate-performance of 75 % (10 A g−1). Furthermore, a button-type supercapacitor (SC) assembled by two pieces of self-supporting CNF(6FAP-6FDA)-1/3 membrane attains an energy density maximum of 11.39 W h kg−1 at a power density of 250 W kg−1. Under 10,000 cycles of charging-discharging, the SC demonstrates an outstanding working stability. In brief, this study reports a novel polymer precursor for the preparation of N, O co-doped active CNFs, and provides an insight into the relationship between the chemical structure, microstructure and electrochemical performance for self-supporting SC electrodes. • The N, O co-doped activated carbon nanofibers were prepared. • The o -hydroxyl polyimides containing rich –C(CF 3) 2 - structures were used as precursors. • The self-supporting electrodes exhibited superior capacitive performances. [ABSTRACT FROM AUTHOR]

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]

Developing a simple and effective method for optimizing lignin structure is a key challenge for the application of biomass-based carbon nanofibers in energy storage and moisture-enabled electricity generation fields. In this work, an effective strategy is designed to prepare novel biomass-based carbon nanofibers. Carbon quantum dots (CQDs) are introduced as functional components into biomass-based carbon nanofibers to optimize the inherent structural defects of lignin. The introduction of CQDs effectively reduces the interaction between lignin macromolecules, thereby increasing the flexibility of lignin macromolecule chain segments. The obtained biomass-based carbon nanofibers exhibit excellent microfiber morphologies and a high degree of graphitization. The specific capacitance and energy density for biomass-based carbon nanofibers as the energy storage device reach 294.4 F/g and 28.3 W h/kg, respectively. Furthermore, the biomass-based moist-electric generator shows high power generation efficiency, the output voltage and output current of a single device reach 0.75 V and 1.8 μA, respectively. Notably, as the number of biomass-based moist-electric generators in series or parallel increases, the overall output efficiency of the device system has a linear relationship, which means that a sufficient number of biomass-based moist-electric generator devices can meet the power supply requirements of larger power systems. This work puts forward a promising strategy to prepare low-consumption, high-performance, and environmentally friendly biomass-based carbon nanofibers for the supercapacitors and moist-electric generators. [Display omitted] • The introduction of CQDs optimize the inherent structural defects of lignin. • CQDs improve the fiber morphology and graphitization degree of carbon nanofibers. • Biomass-based carbon nanofibers exhibit excellent electrochemical performance. • Biomass-based carbon nanofibers can be used for a novel moist-electric generator. • The preparation of novel biomass-based carbon nanofibers was proposed. [ABSTRACT FROM AUTHOR]

Manifold graphene-based supercapacitor (GSC) electrodes have been extensively studied recently. Numerous studies have aimed to improve the performance of GSCs by amending the surface using various treatments or by incorporating diverse materials. However, few studies have been conducted on the treatments for the back electrodes which support the active material in the GSCs. Herein, the activation of carbon nanofibers (CNFs) back electrodes was achieved through simple thermal activation using potassium hydroxide (KOH) as an activating agent to enhance the electrochemical performance of GSC electrodes. The optimized sample exhibited a specific capacitance (C sp) of 210 F/g at 100 mV/s without adversely affecting the self-discharge behavior of the electrodes. Compared to the reference electrodes formed on the nonactivated CNFs, the C sp at high rate operations of the GSC electrodes was markedly increased by 1.6 times. Morphological, elemental, and electrochemical analyses were conducted to study the effects of KOH activation on the performance enhancement of GSC electrodes. Our results present a novel research approach for enhancing GSC performance. [Display omitted] • KOH thermal activation for carbon nanofiber back electrodes was conducted. • An optimum temperature for the activation was found to be 800 °C. • The activation increased the specific capacitance for graphene supercapacitors. • The self-discharging did not worsen, indicating the practicality of this discovery. [ABSTRACT FROM AUTHOR]

Nowadays, great effort has been devoted to designing biomass-derived nanoscale carbon fibers with controllable fibrous morphology, high conductivity, big specific surface area and multifunctional characteristics. Herein, a green and renewable strategy is performed to prepare the biomass-based nanoscale carbon fibers for fire warning sensor, supercapacitor and moist-electric generator. This preparation strategy thoroughly gets over the dependence of petroleum-based polymeride, and effectually improves the energy storage capacity, sensing sensitivity, humidity power generation efficiency of the obtaining biomass-based carbon nanofibers. Without the introduction of any active components or pseudocapacitive materials, the specific capacitance and energy density for biomass-based nanoscale carbon fibers achieve 143.58 F/g and 19.9 Wh/kg, severally. The biomass-based fire sensor displays excellent fire resistance, stability, and flame sensitivity with a response time of 2 s. Furthermore, the biomass-based moist-electric generator shows high power generation efficiency. The output voltage and current of five series connected and parallel-connected biomass-based moist-electric generators reaches 4.30 V and 43 μA, respectively. Notably, as the number of biomass-based moist-electric generators in series or parallel increases, the overall output voltage and current of the device system have a linear relationship. This work proposes a self-powered fire prediction system based on nanoscale carbon fibers that integrates sensing, power generation, and energy storage functions. [ABSTRACT FROM AUTHOR]

Hierarchical MnO 2 -based fiber-in-tube and particle-in-tube nanostructures with unique chemical compositions and gradient pores have been rationally designed and constructed using a simple self-template method for high-performance asymmetric supercapacitors, which deliver extraordinarily excellent energy density. • MnO 2 -based fiber-in-tube and particle-in-tube nanostructures are designed. • The hierarchical architectures are fabricated via a simple self-template approach. • The novel nanotubes yield superior specific capacity as supercapacitor electrodes. • The asymmetric supercapacitors deliver extraordinarily excellent energy density. Manganese dioxide (MnO 2) promises for high-performance asymmetric suprecapacitors, owing to its high theoretical capacity, abundant source, and low cost. However, insufficient practically-achievable capacity and relatively narrow voltage window in alkaline electrolyte are blocking high energy density of MnO 2 -based supercapacitors, where strategies for activating its capacitive performance and widening voltage window are the top priorities to solve the bottleneck problems. Herein, both the fiber-in-tube (NCCM-FiT) and particle-in-tube (NCCM-PiT) nanostructures coulping active NiCoO x nanoparticles and conductive carbon with MnO 2 tubes have been purposely fabricated, using the electrospun nickel cobalt oxides/carbon nanofibers (NCO/CNFs) as the self-template agents for enhanced energy density of MnO 2 -based supercapacitors. These hierarchical hollow nanotubes with gradient pores and unique compositions yield excellent capacitive properties, in terms of a competitive capacity (431.7 F g−1 or 431.7 C g−1, 0.5 A g−1), which is 2.7 times that of the MnO 2 nanotubes-based electrodes. A maximum energy density of 46.4 Wh kg−1 is obtained at the power density of 400 W kg−1 for the asymmetric device assembled with the NCCM-PiT-based positive electrode and the electrospun CNFs-based negative electrode. The remarkable energy density demonstrated by these hierarchical hollow nanotubes exemplifies a novel and effective design in electrode materials for the asymmetric supercapacitors (ASCs) with superior performance. [ABSTRACT FROM AUTHOR]

The development of multifunctional composites is a challenging but necessary path for the miniaturization and integration of electronic products. Herein, versatile bimetal hydroxide (NiCo 2 (OH) 6) nanowires coated on TiO 2 modified lignin based carbon nanofibers (CNFs/TiO 2 @NiCo 2 (OH) 6) have been prepared successfully by the method of electrospinning followed by hydrothermal treatment. The loading of NiCo 2 (OH) 6 , the doping of N, and the modification of TiO 2 endow the CNFs/TiO 2 @NiCo 2 (OH) 6 with multifunctional application in energy storage and microwave absorption (MA). The abundant pores and active sites result in an excellent electrochemical performance with a high specific capacitance of 752.47 F g−1 at 1 A g−1. More importantly, the assembled supercapacitor exhibits a maximum energy density of 60.64 Wh kg−1 and a superior stability of 90.2 % even after 4000 cycles at the current density of 10 A g−1. Moreover, considering the unique porous layered-structure as well as eminent electromagnetic matching properties, as-prepared composites display an excellent MA property, which possesses a minimum reflection loss (RL min) of −46.48 dB and a maximum effective absorption bandwidth (EAB, RL < 10 dB) of 2 GHz (covering 47.62 % of X-band frequency). This work simultaneously delivers the potential application in the field of energy storage and MA. [Display omitted] • Bimetal hydroxide nanowires are grown on TiO 2 modified lignin based CNFs. • TiO 2 doping can enhance the MA properties of composites by improving the permittivity. • The doped TiO 2 generates more micro-defects and oxygen vacancies in CNFs. • The proposed design endows the versatile composites with excellent performance. • Providing a promising approach for the high-value utilization of lignin [ABSTRACT FROM AUTHOR]

Nowadays, materials that possess high activity and natural oxygen vacancy have garnered significant attention as potential electrode materials for supercapacitors. In this study, we successfully prepared the Hf 6 Ta 2 O 17 (HTO) nanofibres (NFs) with an orthorhombic superlattice structure using the electrospinning technique and sintering process. The characterization results indicate that the HTO NFs synthesized at 750 °C show good micro nanostructures and outstanding electrochemical properties. To enhance its energy storage performance, additional oxygen vacancies (OVs) were introduced through a carbothermal treatment under an Ar atmosphere. Although longer reduction reaction times can produce more OVs, the integration of grain boundaries and the growth of grain size caused by large annealing times may limit its electrochemical performance. Therefore, the HTO NFs treated for 1 h (HTO/C-1) exhibited the maximum C s of 925 F·g−1 at 1 A·g−1 with a larger voltage window of 2.1 V. Furthermore, a symmetric supercapacitor fabricated by two reduced HTO NFs electrodes and 1 M Na 2 SO 4 solution, recorded as r-HTO NFs//r-HTO NFs. The device demonstrated excellent energy density of 73.3 Wh·kg−1 (at power density of 1050 W·kg−1) and a long cycling life (81.8% retained after 5000 cycles). These results suggest that the optimized reduction process can provide appropriate oxygen vacancies in HTO NFs, thereby effectively enhancing its performance. [Display omitted] • The Hf 6 Ta 2 O 17 (HTO) nanofibres (NFs) are synthesized by electrospinning method. • The micro nanostructures and electrochemical property of HTO NFs can be designed by controlling the synthesis temperature. • The carbothermal treatment carried under Ar atmosphere is used to improve the amount of oxygen vacancies of HTO NFs. • The HTO NFs treated of 1 h (HTO/C-1) presents excellent capacitance of 925 F·g−1 at 1 A·g−1. • The r-HTO NFs//r-HTO NFs device shows high energy density of 73.3 Wh·kg−1 at power density of 1050 W·kg−1. [ABSTRACT FROM AUTHOR]

The rapid development of consumer electronics, electric vehicles, and smart meters demands high-performance energy storage devices. By now, supercapacitors are expected to become one of the most promising energy devices for future energy technology. In this work, NiO nanoparticles supported on activated carbon nanofibers (NiO/ACNFs) have been synthesized by atomic layer deposition technique, which is directly used as self-supporting binder-free electrodes for supercapacitors. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman results show that NiO nanoparticles (3.1 nm) are uniformly coated on ACNFs. The NiO/ACNFs-600 electrodes demonstrate a specific capacitance of 870 F·g−1 (1 A·g−1) and good rate capability (remain 67% at 10 A·g−1). The asymmetric supercapacitor devices with NiO/ACNFs-600//ACNFs electrodes yield a fairly high energy density of 39.85 Wh·kg−1 at 2000 W·kg−1 and excellent capacitance retention of 87% after 10,000 cycles. The excellent electrochemical capacitance performance for NiO/ACNFs is attributed to the high conductivity and large specific surface area of ACNFs, high capacity, small size, and even dispersion of NiO as well as the synergistic effect between them. These results demonstrate that NiO/ACNFs can serve as excellent electrode materials for high-performance asymmetric supercapacitors. [Display omitted] • NiO is dispersed evenly on lignin-derived ACNFs by ALD for the first time. • The oxygen-containing functional groups of ACNFs provide the active site for the anchoring of NiO. • Combined advantages of porous ACNFs and highly dispersed NiO nanoparticles. • NiO/ACNFs-600 electrode exhibits excellent specific capacitance of 870 F·g−1 (1 A·g−1). • NiO/ACNFs-600//ACNFs device yields outstanding energy density of 39.85 Wh·kg−1 at 2000 W·kg−1. [ABSTRACT FROM AUTHOR]

ZIF derived selenides have become a promising battery-type electrode material, but pure ZIF derived materials tend to agglomerate, averting active sites from full exposure. Herein, a hierarchical Co doped Ni 3 Se 4 on carbon nanofibers modified by ZIF-67 was fabricated by co-electrospinning, calcination and solvothermal synthesis, whose mass ratio of ZIF-67 to PAN and the type of chalcogenides were regulated. Among them, CNF-Co(1:1)@NiSe, with the feature of battery-type materials, displayed the large specific capacitance of 749.27 F g−1 at 0.5 A g−1 and superb rate performance when the current density increased from 0.5 to 10 A g−1, owing to its unique hierarchical structure along with synergistic effect of Co-doped Ni 3 Se 4 , Co-N-C, and CNF. Notably, a solid-state hybrid supercapacitor (CNF-Co(1:1)@NiSe//active carbon) was build, and delivered the maximum energy density of 32.36 Wh kg−1 at 1 A g−1 along with the maximum power density of 7999.99 W kg−1 at 10 A g−1. In addition, the supercapacitor exhibited excellent cycle stability during 5000 cycles and was successfully used for the luminescence of LED, revealing a good application prospect for CNF-Co(1:1)@NiSe. [ABSTRACT FROM AUTHOR]

A facile esterification and electrospinning method is utilized to convert the waste lignin into nitrogen-oxygen co-doped esterified lignin/polyacrylonitrile based carbon nanofibers (E-CNFs). The analysis of FTIR and H1-NMR shows that the esterification reaction occurs between the hydroxyl group and the anhydride group and the ester bond is established in precursor. The lignin after esterification has lower glass transition temperature (Tg), and hence the obtained E-CNFs exhibit inter-fiber bonding structure, higher heteroatom content, and better wettability, rendering an efficient electron transport network and contributing pseudo capacitance. Such unique structure and morphology endow E-CNFs electrode with ultra-high specific capacitance of 320 F g−1 at 1 A g−1 and 200.4 F g−1 at 20 A g−1 with 6 M KOH aqueous as electrolyte, revealing outstanding rate capability. Moreover, the assembled E-CNFs//E-CNFs symmetric supercapacitors using 1 M Na 2 SO 4 aqueous as electrolyte deliver a high coulombic efficiency of 112.5% at the current density 1 A g−1, a remarkable energy density of 17.92 Wh kg−1 at the power density of 800 W kg−1, and excellent cycling stability (∼5.5% loss after 5000 cycles). This inter-fiber bonding structure control strategy provides a perspective and avenue for the further development of high-performance electrode material for supercapacitors applications. High performance supercapacitors are fabricated by carbon nanofibers with inter-fiber bonding structure as electrode materials using a facile esterification and electrospinning method. Image 1 • By change the molecular microstructure to control macroscopic properties. • Building inter-fiber bonding structure to reduce resistance of electrode materials. • Elucidated the mechanism between micromorphology and electrochemical properties. [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]

This work constructs a 1D hollow particle-based carbon nanofibers (HCNFs) derived from Zn-based metal-organic-frameworks (MOFs) particles embedded in biomass-based electrospinning nanofibers as high-performance supercapacitor (SC) electrodes. Abundant mesopores are introduced by the pyrolysis of MOFs, which generates uniformly distributed electrolyte storage pools for a fast electrolyte ions channel. Owing to its uniquely hierarchical pore structure, the derived HCNFs exhibit much enhanced supercapacitive performance. The prepared HCNF-1000 electrode has not only a high specific capacitance (229.6 F g−1 at a current density of 2 A g−1) but also good rate performance (176.8 F g−1 at 10 A g−1, 99.1 F g−1 at 30 A g−1). The two-electrode symmetrical system HCNF-SC has an energy density of 5.1 Wh kg−1 when the power density is 0.5 kW kg−1. HCNF-1000-based solid-state supercapacitor HCNF-FSC shows good electrochemical performance even in different folded states, displaying the potential application value for the development of portable wearable devices. [Display omitted] • The hollow lignin-derived carbon fibers (HCNFs) enhance electrolyte ion transfer. • The rate capability is improved by the abundantly hierarchical pores of HCNFs. • The flexible HCNF-FSC shows promising potential in powering wearable electronics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel nanohaired 3D cobalt hydroxide wheels have been uniformly inserted in CNFs. • Growth process of 3D cobalt hydroxide wheels in CNFs has been proposed. • 3D Co(OH) 2 /CNFs//NGH ASC exhibits high energy density with remarkable cycle life. Abstract Engineering nanostructures in the desired design and suitable size is one of the key issues for persuading high-performance supercapacitors (SCs). In this work, we report a successful synthesis of a new type of nanohaired three-dimensional cobalt hydroxide wheels/carbon nanofibers (3D Co(OH) 2 /CNFs) composite by a cost-effective electrospinning cum hydrothermal method. The 3D Co(OH) 2 wheels are composed of many partially-fused, nanohaired and serrated sheet-like nanoleaflets furnishing abundant active sites. This novel architecture is quite significant for the stability of the composite since the wheels encircle one or more conductive CNFs firmly rather than the simple attachment on the surface of substrate. The growth process of 3D Co(OH) 2 wheels on CNFs has been studied by synthesizing other two novel Co(OH) 2 /CNFs composites. The as-prepared material exhibits a specific capacitance of 1186 F g−1 at a current density of 1 A g−1 with excellent cyclic stability which is the highest reported value for Co(OH) 2 /CNFs composites. The asymmetric supercapacitor (ASC) device assembled using 3D Co(OH) 2 /CNFs as a positive electrode and nitrogen doped graphene hydrogel (NGH) as a negative electrode exhibits a high energy density of 60.31 W h kg−1 at power density of 740.8 W kg−1 which still remains 37 W h kg−1 even at a higher power density of 7500 W kg−1 with remarkable cycle life. Therefore, the composite stands as a promising candidate for SCs electrode material. This unique nanoengineering gives an insight into the synthesis of other stable nanocomposites for diverse applications like sensors, catalysis, etc. [ABSTRACT FROM AUTHOR]

Highly flexible freestanding carbon nanofibers were electroplated with silver for use in supercapacitor applications. The brittle carbon nanofibers were encased within bendable silver shells to provide superior flexibility and resilience of the supercapacitors. The enhanced electrical conductivity derived from the silver shell structure dramatically increased the capacitance of the supercapacitor. The silver shell also conferred structural stability to the carbon core, thus furnishing stable, long-term electrode performance. Nearly 100% of the specific capacitance was retained after N  = 10,000 galvanostatic charge-discharge cycles. The mechanical endurance or stability of the fabricated electrode was evaluated using 1,000 bending cycles, demonstrating that the electrode performance remained unchanged. Cyclic voltammetry and galvanostatic discharge curves were measured at various scan rates and current densities. The fabricated electrodes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, which clearly illustrated the carbon-core and silver-shell structure. [ABSTRACT FROM AUTHOR]

Abstract This paper starts with a review on challenges and need of improved supercapacitor application, which is then followed by advantages of biomass compared with other materials for use in supercapacitor application. The conversion of biomass into carbon nanofiber using different techniques was extensively reviewed for its advantages and limitations. It was revealed that the materials currently used are yet to be fully sustainable or feasible for energy storage application. In contrast, biomass represents a widely available and sustainable material to be converted into carbon nanofiber for energy storage application. Different techniques were employed for carbon nanofiber production to achieve different objectives, comprising high product yield, feasible diameter adjustment, low electric consumption, and shorter production time. Nevertheless, it was revealed that many key properties of the biomass-derived carbon nanofiber have yet to be fully investigated, as there are still knowledge gaps to be filled for each technique. Thus, more studies are needed to broaden the existing understanding in the key parameters of different techniques in order to develop a highly desirable carbon nanofiber from biomass for sustainable energy storage application. Graphical abstract Image 1 Highlights • Challenges and use of biomass in supercapacitor application are reviewed. • Techniques to convert biomass into carbon nanofiber are reviewed. • Biomass is a promising carbon nanofiber material for energy storage application. • Different techniques are used for high product yield and low production cost. • Limited study on many key properties of biomass-derived carbon nanofiber. [ABSTRACT FROM AUTHOR]

With increasing demand for sustainable energy, it is essential to develop low cost, high performance, and environment-friendly materials for energy storage application. Metal oxides and sulfides are mostly being used as electrode materials for energy storage devices. However, their wide applications are precluded due to their higher cost, low stability, and adverse effect on the environment. Therefore, development of environment-friendly supercapacitors with low cost, high performance, and stable performance is a big challenge. Here, we report surface engineered carbon nanofibers for durable and high-performance supercapacitor. Surface engineered carbon nanofibers showed the highest specific capacitance of 277 F/g (at 1 mV/s), along with superior flexibility and cyclic stability. Moreover, they showed high energy and power density of 30.5 Wh/kg and 8.3 kW/kg, respectively. The cyclic stability showed almost 100% retention in charge storage capacity up to 5000 cycles. Electrochemical properties of a fabricated symmetrical supercapacitor device using these carbon nanofibers showed improved charge storage capacity at elevated temperatures. The charge storage capacity improved by over 150% by increasing temperature from 10 to 60 °C. Our results suggest that surface engineered carbon nanofibers could be a potential candidate for higher performance and durable supercapacitors. [ABSTRACT FROM AUTHOR]

Flexible electrode materials play an important role in flexible portable energy storage devices. Carbon-based nanofiber has attracted numerous attentions due to its advantages on flexibility, safety, and reliability. Herein, we reported a novel and simple method to fabricate nitrogen-boron co-doped hollow porous carbon nanofiber (HPCNF) membranes as flexible supercapacitor electrodes. The higher specific surface area (413.98 m2/g) of HPCNF and the co-doping of N and B resulted in a high specific capacitance of 200.2 F/g (0.1 A/g). After 3000 cycles, NB-HPCNF still maintained high capacitance retention (104.81%). This study provides a new idea for electrochemical energy storage, which is beneficial to the deeper development of portable flexible devices. [Display omitted] • A novel and simple method was used to fabricate nitrogen-boron co-doped hollow porous carbon nanofiber membranes. • The well-developed hollow channels facilitated fast and efficient charge transport in carbon nanofibers. • A solid-state symmetric supercapacitor has good electrochemical properties and good mechanical stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Direct laser writing carbonization and heating treatment are used to manufacture carbon fibers. • Heat treatment can increase the specific surface area of carbonized lignin fiber. • A flexible supercapacitor constructed of carbon fibers has the qualities of being light, thin, and breathable. Electrode materials significantly impact supercapacitor performance and developing high-performance electrode materials is crucial in energy storage. Commonly used laser-induced electrode materials are currently limited by severe contamination and hard-to-change intrinsic properties. This paper proposes a method for fabricating high-performance supercapacitors by laser carbonizing the lignin composite fiber membranes with heating treatment. Lignin fiber can achieve superior tensile strength, stiffness, and carbonization degree under suitable heat treatment temperatures. Heat treatment at 450 °C has been proven to be the ideal temperature for supercapacitor performance. At a current density of 1 A/g, the supercapacitor can reach the highest specific capacitance of ∼391.2F/g. In addition, doping MoS 2 boosted the device's performance to a specific capacitance of ∼527.8F/g, a power density of ∼500 W/kg, and an energy density of ∼73 Wh/kg at the same current density. In addition, lignin fibers are ideal materials in electronic textiles due to their soft, thin, and breathable properties. This study provides supportive evidence and technical guidance for improving the performance of flexible wearable supercapacitors. [ABSTRACT FROM AUTHOR]

The composites of transition metal oxide and carbon nanofibers (CNF) are promising electrode materials for supercapacitors in alkali solutions. However, the weak binding and unsatisfactory rate performance limit their application. To improve the weak binding, this study prepared the SiO 2 -modified carbon nanofibers (Si 1 -C) via electrospinning. Then the fully encapsulated CoO-NiO (NiCo@Si 1 -C) was fabricated on Si 1 -C by solvent-thermal and calcination. As is revealed, CNF containing SiO 2 is conducive to forming a full coverage of CoO-NiO coating with a stacked petal structure. More importantly, nano-SiO 2 plays the anchoring role of NiO-CoO and CNF, making the combination more firmly. The NiCo@Si 1 -C delivers a specific capacitance of 518.1 F g−1 at 0.5 A g−1, almost 2.25 times that of NiCo@Si 0 -C (229.9 F g−1 at 0.5 A g−1). When the current density increases to 50 A g−1, it is only 3.9 % lower than the capacitance (497.9 F g−1), which means a high rate performance. Moreover, asymmetric supercapacitor devices are assembled with activated carbon (NiCo@Si 1 -C//AC) with an energy density of 11.7 Wh kg−1, even at a high power density of 14,000.7 W kg−1. [Display omitted] • Nano-SiO 2 plays the anchoring role of NiO-CoO and CNF, making the combination more firmly. • The NiCo@Si 1 -C has a unique all-encapsulated CoO-NiO with a stacked petals structure. • The NiCo@Si 1 -C has ultra-high rate performance. [ABSTRACT FROM AUTHOR]

Waste crab shell (CS) is implemented to prepare highly N‐doped and CS‐derived hierarchical porous carbon nanofibers (CSCNs) capable of high‐performance supercapacitors combining with Co3O4 nanocrystals. The fiber nature of the exoskeleton of CSs is transformed to N‐containing organic nanofibers, which are carbonized and subsequently activated by hot CO2 treatment to control the specific surface area (SSA) and pore size distribution (PSD). The interwoven bundles of CSCNs present intrinsic macroporosity whereas mesopores (<10 nm) are generated at the interspace between CSCNs. The CO2‐activated CSCNs show an ultra‐high SSA of 2430 m2/g, combining with N‐doping levels of 2.1 wt %. In addition, highly N‐doped hierarchical CSCNs are utilized as supercapacitors hybridized with Co3O4 nanocrystals (Co3O4@CSCN). The Co3O4@CSCN exhibits superior capacitances of 508 F/g at 1 A/g, outstand rate capacitances and 374 F/g (74%) even at 50 A/g, and excellent long‐term cycling stability of 470 F/g (95%) at 2 A/g over 10 000 cycles. Such excellent electrochemical performance is attributed to the synergic effect of redox sites and electric double layer capacitance of highly porous CSCNs, augmented electric conductivity and wettability due to N‐doping, enhanced charge transfer caused by small crystal sizes and large interfaces of CSCNs, and easy electrolyte diffusion due to the genuine hierarchy of CSCN. [ABSTRACT FROM AUTHOR]

A freestanding, binder-free carbon nanofibers@polypyrrole@reduced graphene oxide (CNFs@PPy@rGO) core-double-shell supercapacitor electrode is prepared by carbonization of electrospun PAN nanofibers network follow by the electrochemical deposition of PPy and then reduced graphene oxide layer coating. The flexible all-solid-state supercapacitor based on the CNFs@PPy@rGO core-double-shell electrode with PVA/H 3 PO 4 gel electrolyte demonstrates a highest specific capacitance of 188 F/g at the scan rate of 2 mV/s and good cycling stability. Due to the synergistic effect of three materials, the newly designed composite electrode shows the highest specific capacitance of 336.2 F/g at the scan rate of 2 mV/s, which increases by 10% than that of CNFs@PPy electrode (302.7 F/g) at the same scan rate in a three-electrode system. Furthermore, it shows excellent cycling stability performance with 98% capacitance retention after 2500 cycles, which is better than that of CNFs@PPy electrode (90%). [ABSTRACT FROM AUTHOR]

Iron sulfide, commonly known as fool's gold, is rapidly emerging as an attractive material for both energy conversion (in photovoltaics) and energy storage, especially as an electrode in lithium-ion batteries. In this manuscript, we report on a simple one-pot two-step technique for synthesis of carbon nanofiber (CNF) cross-linked FeS 2 networks, by microwave pyrolysis of ferrocene to iron decorated CNF and its subsequent sulfidation by a sustainable source, namely, l -cysteine. When used as the negative electrode in lithium-ion batteries, our 3D mesoporous FeS 2 –CNF hybrids exhibit high capacity of 994 mAhg −1 even after 300 cycles, which exceeds the theoretical capacity of FeS 2 (894 mAhg −1 ). Additionally, when applied as super-capacitor electrodes, our microwave-synthesized FeS 2 –CNF electrodes exhibit high capacitance of 612 and 342 Fg -1 at 5 and 100 mVs −1 , respectively, and long-term cyclability, with 97% capacitance retention after 2000 cycles. [ABSTRACT FROM AUTHOR]

Flexible supercapacitors with both high energy and high power densities are critical for flexible electronics. In this paper, hybrid flexible carbon nanofibers decorated with NiCo 2 S 4 nanoparticles are successfully prepared by combination of electrospinning, carbonization and hydrothermal treatments. The obtained hybrid carbon nanofibers display remarkable specific capacitance (527.8 F g −1 at the current density of 0.2 A g −1 and 622.5 F g −1 at 2 mV s −1 ), good rate capability (310.5 F g −1 at 4.0 A g −1 ) and excellent cycle stability (retaining 90.0% after 3000 cycles). The flexible asymmetric supercapacitors based on carbon nanofibers decorated with NiCo 2 S 4 and porous carbon nanofibers coated with activated charcoal are fabricated. The combined unique properties of each of these components enable highly flexible and mechanically strong films that can serve as electrodes directly without using any current collectors or binders. The fabricated device shows an energy density of 32.1 Wh kg −1 at power density of 67.6 W kg −1 and cycle stability retaining 88.5% after 1500 cycles at 1.0 A g −1 . Therefore, the novel flexible asymmetric device with perfect flexibility and stability can be applied as one of the most promising power supplies. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of core-shell SnO x /carbon nanofiber (CNF) composite mats via single-nozzle one-step electrospinning for use as flexible freestanding electrodes in supercapacitors. The freestanding and flexible nature of the composites is essential for their use in lightweight, portable, and foldable electronic devices and eliminates the need for a separate current collector. We fully characterized the structural and morphological properties of the SnO x /CNF mats and optimized the SnO x to CNF precursor ratio. The optimized SnO x /CNF-based symmetric supercapacitor exhibited a capacitance of 289 F·g −1 at a scan rate of 10 mV·s −1 . Moreover, it retained more than 88% of its initial capacitance after 5000 cycles, highlighting the long-term stability of supercapacitors based on these SnO x /CNF mats. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of a MnO x /carbamide carbon nanofiber (CCNF) composite consisting of MnO particles embedded in CCNFs as a highly flexible and freestanding electrode material for supercapacitors. A sacrificial polymer component, polymethylmethacrylate, included in the precursor solution, pyrolyzes during heating, resulting in pores in the fibers, some of which are filled by the MnO nanocrystals. Carbamide is added to control the size of the MnO x particles as well as to increase the carbon content of the composite and hence its conductivity. The X-ray diffraction and Raman spectra of the composite show that the MnO particles formed have low crystallinity. Transmission electron microscopy confirms that the MnO particles are distributed very uniformly over the CCNFs. Symmetric supercapacitors constructed using electrodes of this composite exhibit specific capacitances of 498 F∙g −1 at a scan rate of 10 mV∙s −1 and 271 F∙g −1 at a current density of 1 A∙g −1 . They also exhibit excellent long-term cycling performance, retaining 93% of their initial capacity after 5000 cycles of galvanostatic charging/discharging. [ABSTRACT FROM AUTHOR]

Electrospun carbon nanofibers (CNFs) present an attractive application for energy storage devices. However, current CNFs suffer from poor graphitic structure. In this work, the graphitic structure was improved by adding a small amount of graphene oxide (GO) into water-soluble phenolic resin to prepare flexible carbon nanofibers prior to processing. The obtained CNFs exhibit improved electrochemical performance compared with pristine carbon nanofibers. The flexible hybrid membranes with NiMoO 4 uniformly anchored give rise to a high specific capacitance (593 F g −1 at 1 A g −1 based on the mass of hybrid membranes), good rate performance (465 F g −1 at 10 A g −1 ) and intriguing cycling stability (95.4% after 2000 cycles), simultaneously. The symmetric solid-state supercapacitor fabricated by using the as-prepared hybrid membrane had a maximum energy density of 9.3 Wh kg −1 and a power density of 3430.6 W kg −1 . It also possessed high rate capability of 92.4% with the current density ranging from 0.2 to 10 A g −1 , as well as excellent cyclic lifetime over which 80.8% of the capacitance were maintained after 5000 cycles at 5 A g −1 . [ABSTRACT FROM AUTHOR]

• HC is used to prepare porous carbon for SCs for the first time. • A SSA of 3272 m2/g with a capacitance of 227 F/g is maximumly achieved. • HC/KOH treatment doubles the performance of SCs compared with sole KOH activation. • HC is a potential preparation method of porous carbon with high efficiency. Hydrodynamic cavitation (HC), which can effectively induce sonochemical effects, is widely considered a promising process intensification technology. In the present study, HC was successfully utilized to intensify the alkali activation of GPs for SCs, for the first time. Five BDCMs were synthesized following the method reported in the literature. For comparison, four more BDCMs with HC-treated, among which a sample was further doped with nitrogen during the HC treatment, were prepared. Then all the samples were compared from microscopical characteristics to electrochemical performance as SCs materials. The morphology study demonstrated that the HC treatment had created many defects and amorphous carbon structures on the GP-based BDCMs, with the highest SSA reaching 3272 m2/g (1:6-HCGP), which 32 folded that of the Raw carbon sample's. The HC treatment also intensified the N-doping process. XRD and XPS results manifested that the N content had been increased and consequently changed the electronic structure of the carbon atoms, leading to the increase of specific capacitance (1:6-HCGP+N-based SC, 227 F/g at 10 A/g). The cycle performance proved that the GP-based BDCMs have long-term stability, indicating that the HC-treated BDCMs were good choices for energy storage technologies. Compared with the ultrasound-assisted method, which may have a high energy density, the HC-assisted method enables high production and energy efficiency. This work is a first time attempt towards the industrial application of HC method in energy-related materials synthesis and encourages more in-depth studies in the future. [ABSTRACT FROM AUTHOR]

Porous carbon nanofibers (PCNFs) have been the hotpot material for supercapacitor due to their porous structure, outstanding conductivity, excellent electrochemical properties, and high specific surface area. The template method is a facile approach to prepare PCNFs through blending a thermally decomposable substance, subsequently heating treatment. High amylose starch (HAS) is a natural carbohydrate including carbon, hydrogen and oxygen elements. Herein, a simple template method utilizing HAS as the sacrificial polymer to prepare porous carbon nanofibers with high specific surface areas has been reported. The resulted carbon nanofibers have a hierarchical micro/meso porous structure with high level of microporous pores, more importantly, their specific surface area can reach 1204 m2 g−1. The electrochemical performances of PCNFs electrodes are studied using a three-electrode system and button-type devices. The specific capacitance of carbon nanofiber electrode is 344 F g−1 at 1.0 A g−1 when 20 wt% HAS is added. The cycling durability of corresponding device is 99.9% capacitance retention after 10000 cycles. And the maximum energy density of 12 Wh kg−1 is obtained at a lower power density of 125 W kg−1. As a green natural material, HAS may provide a low-cost solution to prepare high-performance carbon nanofibers for energy storage applications. [Display omitted] • An in-situ activation method is used to prepare hierarchical micro/meso porous carbon nanofibers. • High amylose starch can be as a sacrificial polymer to prepare carbon nanofiber with a high specific surface area. • Supercapacitor electrodes prepared from the carbon nanofibers show large specific capacitance and excellent durability. [ABSTRACT FROM AUTHOR]

A multilayered carbon nanosphere (CNS)/manganese oxide (MnO 2 ) nanofilm is fabricated by a newly developed layer-by-layer (LBL)–post-infiltration approach. The multilayered architecture effectively shortens the length over which ions diffuse, and the nanoscaled carbon/MnO 2 interface provides an interconnected pathway for electron conduction. MnO 2 acts not only as the redox center for charge storage, but also as the spacer between the LBL-assembled multilayers for more rapid electrolyte transport. A specific capacitance (based on MnO 2 ) of 1134.0 F g −1 is achieved at a loading of 5.22 μg cm −2 in a neutral electrolyte. This strategy provides a promising approach for fabricating high-power and high-energy electrochemical capacitors with precise control of electrode thickness on geometric device surfaces. [ABSTRACT FROM AUTHOR]

We have reported a fast and eco-friend method to synthesize the MnO 2 on catalytically grown carbon nanofiber (CGCNF). The CGCNF was functionalized by acid treatment under various H 2 SO 4 /HNO 3 ratios. A microwave-assisted hydrothermal method was then used to synthesize MnO 2 /CGCNF composites at a very short time of 5 min. We demonstrated that the surface modification has significant effect on the MnO 2 deposition and the electrochemical performance of the resulting MnO 2 /CGCNF composites. Electrical impedance spectroscopy analysis and cyclic voltammetry showed that O-functional group controls the electrical conductivity and the electrochemical performance of both CGCNF and CGCNF/MnO 2 composites, respectively. It was found that C O bond assists the MnO 2 deposition. CGCNF/MnO 2 composite showing specific capacitance (Csp) of 257 F/g at a scan rate of 5 mV/s and electrical resistance of 19 Ω was demonstrated. [ABSTRACT FROM AUTHOR]

Cross-linked carbon nanofiber (CLCNF) was successfully prepared by directly carbonizing electrospun polyacrylonitrile (PAN) nanofiber. Comparing to non-cross-linked carbon nanofiber (NCLCNF) obtained via carbonizing of pre-oxidation PAN nanofiber, CLCNF shows better conductivity owing to its cross-linked structure. Then CLCNF was used as scaffold to support polyaniline (PANi) nanorods for supercapacitor electrode material. The hierarchical CLCNF/PANi composite displays a capacity of 206C g −1 at 0.5 A g −1 with excellent rate capability (remains 49% even at 800 A g −1 ), which is much higher than that of NCLCNF/PANi composite (17%). More interestingly, supercapacitor device based on CLCNF/PANi composite achieves 75.3% capacity retention after 10000 charge-discharge cycles at 10 A g −1 , suggesting excellent cycle stability. All these experimental results indicate that this method for fabricating CLCNF is a substantial advancement towards the practical applications of carbon nanofiber in energy conversion and storage field. [ABSTRACT FROM AUTHOR]

A hybrid of silica decorated on porous activated carbon nanofibers (ACNFs) is fabricated in the form of a web via electrospinning and an activation process as an electrode material for electrochemical capacitors in an organic electrolyte. The introduction of PhSiH 3 (PS) into the polyacrylonitrile (PAN) solution induces a porous ACNF structure containing silica nanoparticles (NPs) via the spontaneous sol-gel process of PS by steam in the subsequent physical activation process. These inorganic-organic hybrid composites of porous ACNF containing silica NPs show superior specific capacitance and energy density in electrochemical tests, along with good rate capability and excellent cycle life in an organic electrolyte, which is attributed to the combination of ACNF's high surface area and silica's hydrophilicity. The electrochemical performance decreases with increasing PS concentration, and this trend is consistent with the specific surface area results, which reveal the rapid formation of a double layer. [ABSTRACT FROM AUTHOR]

Polyaniline is grafted onto the surface of high conductivity carbon nanotube-embedded carbon nanofibers (PANi-P-1.0) via plasma modification to fabricate an electrode for a high performance supercapacitor. The structure and morphology of polyaniline graft onto the carbon nanofiber (CNF) are confirmed by Raman, X-ray photoelectron spectroscopy, electron microscopy and transmission electron microscopy. The emeraldine base form of nanorod-polyaniline is well-distributed on the surface of the CNF. The PANi-P-1.0 has a high specific capacitance of 606 Fg −1 . From the result of the electrochemical properties, the high capacitance is contributed by the electric double layer capacitance of the high conductivity CNF and the pseudocapacitance of the grafting polyaniline. In addition, compared to polyaniline coated on the surface of the CNF, the electrochemical properties of the PANi-P-1.0 are improved by reducing the charge transfer resistance (Rct) from 13.54 to 3.87 Ω, the Warburg coefficient from 101.39 to 47.96 Ωs −1/2 and the relaxation time constant from 0.794 to 0.194 s due to the covalent bond between the polyaniline and CNF. The PANi-P-1.0 also show excellent cycling stability after 1,000 cycles of galvanostatic charge and discharge because the free space around the grafting polyaniline allows volumetric change. [ABSTRACT FROM AUTHOR]

The main objective of this work is to prepare a flexible supercapacitor using electrochemically synthesized pyrrole formyl pyrrole copolymer P(Py-co-FPy) coated on the carbon microfibers. Due to difficulties of working with carbon microfibers, glassy carbon was used to find out optimized conditions by varying mole ratio of pyrrole and formyl pyrrole monomers on the capacitance value. The prepared electrodes were characterized using Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FESEM), Brunauer–Emmett–Teller (BET) analysis, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Then the X-ray photoelectron spectroscopy (XPS) was used to characterize the optimized electrode. The specific capacitance is calculated using cyclic voltammetry, charge/discharge method, and impedance spectroscopy. The charge/discharge study reveals that the best specific capacitance is estimated to be 220.3 mF cm −2 for equal mole fraction of pyrrole and formyl pyrrole Py (0.1)-FP (0.1) at discharge current of 3 × 10 −4 A. This optimized electrode keeps about 92% of its capacitance value in high current of discharging. The specific capacitances calculated by all the mentioned methods are in agreement with each other. Finally, the found optimized conditions were successfully applied to produce a flexible supercapacitor on the surface of carbon microfibers. [ABSTRACT FROM AUTHOR]

In this work, a free-standing, flexible and highly conductive vanadium-carbon nanofiber composite has been fabricated as electrode for Supercapacitors. Vanadium monoxide (VO) coupled with amorphous vanadium covalent bonds (VO x ) are successfully incorporated into carbon nanofibers (VO/VO x /CNF) by electrospinning and heat treatment. A theoretical explanation is proposed for the formation of VO/VO x in CNF composites. The VO and VO x are respectively reduced and formed from vanadium precursors of vanadium dioxide (VO 2 ) and vanadyl (IV) acetylacetonate (VOA) by means of self-reduction method, in which carbon precursors (polyacrylonitrile and polyvinylpyrrolidone), small evolved gas molecules (CO, H 2 , HCN) and graphitized carbon act as self-reductants. No additional reductants is needed before or after heat treatment, avoiding the secondary contamination. The VO/VO x /CNF electrode has a specific capacitance of 325.7 F g −1 at a current density of 1 A g −1 and is capable of reserving 92% of its initial capacitance after 5000 cycles operating at a current density of 4 A g −1 in a symmetric two-electrode capacitor using 6 M KOH as an electrolyte. The superior electrochemical performance of VO/VO x /CNF may be attributed to two advantages. The first is the enhanced conductivity brought upon the incorporation of quasi-metallic VO (∼ 10 2 Ω −1 cm −1 ) and the network of nanowire, and the second is the rapid ion transfer rate caused by the rich vanadium redox couples VO/VO x and the well-developed pore structure. Notably, this work has also provided a facile method to obtain varaible low valence states from vanadium oxides through self-reduction, which may also be applied to synthesize other metal oxides-carbon nanofiber composites. [ABSTRACT FROM AUTHOR]