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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]

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]

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]

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]

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]

One-dimensional hierarchical porous carbon nanofibers (CNFs) embedded with Co 3 O 4 nanoparticles in a hollow channel (PPMCo) are fabricated by coaxial electrospinning followed by thermal treatment. The degree to which the CNF surface is exposed to Co 3 O 4 nanoparticles was controlled by the cobalt(II) acetate concentration. The well-controlled structure of PPMCo with porous structure, heteroatoms, and amorphous Co 3 O 4 nanoparticles provided fast ion transport and large reaction surface area, resulting in effective ion migration to the active site and a high rate capacity of the electrode. Benefitting from the unique structure, the PPMCo supercapacitor electrodes displays a high specific capacitance of 188 Fg−1 at 1 mAcm−2, rate capability of 82% when the current density is increased from 1 to 20 mAcm−2, and cycling stability of 93% for 10,000 cycles. The good capacitive performance of the PPMCo electrode is attributed to the synergistic effect of the hierarchical porosity, electroactive material of Co 3 O 4 , high effective surface area, and polar effects by heteroatoms. [Display omitted] • Hierarchical porous CNF embedded with Co3O4 was prepared by coaxial electrospinning. • The degree of CNF exposed to Co3O4 was controlled by the Co(OAc)2 concentration. • The hollow core of the core part provides a fast electron transport channel. • Amorphous Co3O4 helps transport ions by reducing the charge transfer resistance. • The heteroatom functional groups on the carbon surface enhance the pseudocapacitance. [ABSTRACT FROM AUTHOR]

Achieving high specific surface area and ion accessibility in graphene-based electrodes with a high mass loading for supercapacitors poses a significant challenge because strong π-π stacking of graphene sheets often blocks the access of electrolyte ions to active sites. Herein, we report a novel protocol to prepare free-standing laminated graphene/carbon nanofiber films as high areal mass-loading electrodes through a layer-by-layer electrospinning technique. The unique laminated structure of graphene/carbon nanofiber thin films can enhance electrolyte penetration and increase transportations of ions/electrons. The symmetric supercapacitors (SCs) using the as-obtained graphene/carbon nanofiber films as electrodes reach areal specific capacitance of 1536 mF cm−2 at a current density of 1 mA cm−2. Most importantly, the areal energy density of the SCs can reach 0.22 mWh cm−2 at a power density of 1 mW cm−2 with a high areal mass loading of 24 mg cm−2. The exceptional electrochemical properties of the laminated graphene/carbon nanofiber films render them promising materials for electrodes in SCs. [Display omitted] • Laminated graphene/CNFs were prepared via layer-by-layer electrospinning. • The unique laminated structure enhances ions accessibility at high mass loading. • The assembled symmetric supercapacitor exhibits high areal specific capacitance. [ABSTRACT FROM AUTHOR]