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Vanadium Nitride (VN) is attractive for energy storage due to its high conductivity (1.6 × 106 S/m) and specific capacitance (1350 F/g) but limited to alkaline electrolytes for redox. In contrast, V 2 O 3 is redox active but not very conductive. In these hybrids a mixture of VN and vanadium oxide (V 2 O 3) were encapsulated in electrospun carbon-nanofibers. A combination of VN and V 2 O 3 takes advantage of the high conductivity from VN and the redox activity from V 2 O 3. Additionally, having the vanadium encapsulated within the carbon can help with the stability as the electrolyte will not have direct interaction with the surface. These hybrids were made by in-situ nitridation of the encapsulated V 2 O 5 followed by ex-situ activation with carbon dioxide. The hybrids were characterized by XPS and Raman spectroscopy. Hybrids of VN/V 2 O 3 -CNF showed increased capacitance of 245 Fg−1 with energy and power densities of 70.2 Wh kg−1 and 1751 W kg−1 in ionic liquid electrolyte. The devices showed good cycle stability with ∼90 % retention after 10,000 cycles at a current density of 1 Ag−1. These findings highlight the potential of VN/V 2 O 3 -CNF hybrids as high-performance supercapacitor electrodes. The combination of high conductivity and redox activity, along with encapsulation within CNFs, opens promising avenues for advanced energy storage. [ABSTRACT FROM AUTHOR]

The synthesis of Laser-Induced Graphene (LIG) through the laser ablation process of carbon-containing materials is a rapid and scalable process which enables the production of graphene in a cost-effective manner. In recent years, metal oxide – graphene composite electrodes have gained a lot of importance due to their use in various Energy Storage Devices (ESDs). In our investigation, we manufacture composite electrodes of manganese dioxide (MnO 2) and LIG through a hydrothermal process and use it as electrodes in Flexible Supercapacitors. This method deviates from traditional procedures as it eliminates the requirement for binders in creating composite electrodes, given that MnO 2 can be directly deposited onto the LIG electrodes. The assembled all-Flexible Supercapacitor (FSC), featuring unique LIG-MnO 2 composite electrodes, showcased a remarkable areal capacitance of 66.5 mF cm−2 at 5 mV s−1 scan rate. The device also exhibited a very high areal energy density (2.3 mWh cm−2) and power density (19.7 mW cm−2) at 0.2 mA cm−2 current density. Also, 82 % capacitance retention was observed at the end of 2000 cycles and the device also exhibited a good flexibility during bending tests, as evidenced by an 80 % capacitance retention after 100 bending cycles. [ABSTRACT FROM AUTHOR]

• MnO 2 /CNF/Ag nanofabric electrodes are developed for flexible supercapacitors. • The brittle issue in the CNF electrode is greatly improved by an Ag incorporation. • The optimized MnO 2 /CNF/Ag electrode has a specific capacitance of 184 F/g at 1 A/g. • An energy density of 16.3 Wh/kg and a power density of 400 W/kg was achieved. • A capacitance retention rate of 87 % was demonstrated when subjected to bending. Flexible supercapacitors are gaining increasing popularity due to their potential in powering portable, wearable, and lightweight electronic devices. In this study, we have successfully developed a high-performance flexible electrode for quasi-solid-state supercapacitors by incorporating Ag into carbon nanofibers (CNF) through electrospinning, and growing MnO 2 as an active material on the electrode using an in-situ redox method. The Ag and MnO 2 co-decorated CNF electrode offers several advantages over conventional CNF electrodes, including an enlarged reaction area, higher charge storage capacity, and improved resistance to brittleness issues. Among all the quasi-solid-state supercapacitors tested, the MnO 2 -decorated electrode with an optimized Ag incorporation exhibited the highest specific capacitance of 184 F/g at a current density of 1 A/g, representing a remarkable 17-fold increase compared to the reference CNF electrode. Furthermore, the Ag and MnO 2 co-decorated electrode demonstrated an energy density of 16.3 Wh/kg and a power density of 400 W/kg at the same current density. Notably, the electrode exhibited excellent flexibility, with a capacitance retention rate of 87 % when subjected to bending with a curvature ranging from 5 to 1.25 cm. Our results suggest that the Ag and MnO 2 co-decorated CNF electrode holds great promise for flexible energy storage applications. [Display omitted] [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]

With the rapid development of lightweight, portable, and even wearable electronics, there is an increasing demand for flexible supercapacitors with excellent electrochemical performance. Here, we present the design and preparation of a novel architecture with SnO 2 dots uniformly confined on the activated porous carbon nanofibers (CNFs) using copper and its oxides as the hard templates for generating holes. Not only does the single electrode itself with a certain loading mass of SnO 2 show larger specific capacitance, better rate capability, and higher conductivity than the bare CNFs and activated CNFs/SnO 2 electrodes, but the assembled quasi-solid-state symmetric supercapacitor also exhibits good flexibility as well as superior electrochemical property with satisfactory energy density and favorable cycling stability, which indicates the great potential for practical applications. This work may provide a versatile and low-cost strategy to construct carbon/metal oxide nanostructures with robust binding force at the interface for adhesive-free supercapacitors. A novel architecture with SnO 2 dots tightly and uniformly confined on the activated porous carbon nanofibers was prepared using copper and its oxides as the hard templates for generating holes, which can be directly applied as the binder-free electrode for high-performance supercapacitor with excellent flexibility. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Mesoporous ribbon-shaped graphitic carbon nanofibers (MRCNFs) have been prepared by combination of electrospinning technique, template method and catalytic graphitization of transition metal. Transition metal Co, originated from Co(NO 3) 2 ·6H 2 O doped in spinning solution, serves as both template of mesopores and catalyst for graphitic structure. The microstructure of MRCNFs has been optimized by adjusting doping amount of Co(NO 3) 2 ·6H 2 O. The resultant MRCNFs present a relatively centralized distribution of 2–10 nm mesopores, modest specific surface area of 463 m2 g−1 and pore volume of 0.575 cm3 g−1. In addition, considerable nitrogen- and oxygen-containing functionalities (2.88 at.% of N and 4.88 at.% of O) are detected on MRCNFs. In view of electrode materials for supercapacitors, as-obtained ribbon-shaped morphology, mesoporous structure, considerable surface heteroatom-containing functionalities and high graphitization degree synergistically enhance the electrolyte ion diffusion and electron conduction. In a three-electrode test system, the resultant MRCNFs electrodes exhibit high specific capacitance (228 F g−1 at 0.2 A g−1), rate capability (of 58% capacitance retention at 20A g−1) and excellent cycle stability(of 95% capacitance retention after 5000 cycles at 2 A g−1). Graphical abstract Image 1 Highlights • Mesoporous ribbon-shaped graphitic carbon nanofibers (MRCNFs) have been prepared. • Co particles serves as template of mesopores and catalyst for graphitic carbon. • With SSA of 463 m2 g−1, MRCNFs present a capacitance of 228 F g−1 at 0.2 A g−1. [ABSTRACT FROM AUTHOR]

ZnMn 2 O 4 is regarded as one of the potential anode materials for lithium-ion batteries (LIBs), due to its high theoretical specific capacity (784 mAh g −1 ). Unfortunately, the bulk ZnMn 2 O 4 presents an inferior electrochemical performance resulting from the large volume change during the charge-discharge process. In this paper, we report the synthesis and electrochemical properties of ZnMn 2 O 4 nanoparticles (NPs) that are homogeneously distributed in connective network porous carbon nanofibers wrapped by reduced graphene oxide sheets. The distinctive structure of this composite not only provides enough voids to storage Li-ions and buffer the volume expansion of the ZnMn 2 O 4 NPs, but also offers a continuous conducting network for Li-ion and electron transportation, resulting in significantly improved electrochemical performances. As binder-free electrodes for LIBs, an optimized ZnMn 2 O 4 @rGO-CNFs sample exhibits a reversible capacity of 1142 mAh g −1 at 100 mA g −1 over 100 cycles, and a stable capacity of 659 mAh g −1 after 1000 cycles at a large current density of 2000 mA g −1 , enabling ZnMn 2 O 4 a promising electrode candidate for LIBs. [ABSTRACT FROM AUTHOR]

In most of the porous carbon based electrode materials reported to date, the pores were open and directly exposed to electrolyte, and the materials suffered from a huge stress during long-term cycle at a large current density. These would inevitably cause an irreversible damage to the material structure, resulting in a dramatic capacity fade. In this work, the metal oxides composite nanofibers are first fabricated using an electrospinning technique, and then an oxidative polymerization of dopamine and a subsequent calcination are conducted to form a protecting shell. The inner carbon nanofibers have been obtained after removing the metal oxides nanoparticles. Owing to the robust dense carbon shell and inner porous carbon framework as well as intrinsic nitrogen doping, the prepared nanofibers electrode delivers high capacitances of 328 F g −1 at 1 A g −1 and 160 F g −1 even at an extremely high current density of 100 A g −1 in a 6 M KOH aqueous solution. The electrode maintains 77% of the initial capacity after 5000 cycles at 5 A g −1 . The assembled symmetric supercapacitor exhibits a high capacitance of 97.9 F g −1 at 1 A g −1 and still maintains at 60 F g −1 even at a high current density of 50 A g −1 . 73% of the initial capacitance is remained after 5000 cycles at a current density of 10 A g −1 . The experimental results reveal that the inner porous carbon nanofibers may be a promising electrode material for high-rate supercapacitors. [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]

A non-woven network of porous nitrogen-doping carbon nanofibers (PNCNFs) is prepared by electrospinning of polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP), followed by stabilization and carbonization. The specific surface areas, porosity and nitrogen content of PNCNFs can be easily controlled by adjusting the content ratio of PVP to PAN. The non-woven PNCNFs based network provides abundant interface sites and hierarchical porosity for solvated ions. In a three-electrode configuration, PNCNFs-2-3 provides a high specific capacitance of 198 F g −1 at 1 A g −1 in 6 M KOH. A two-electrode configuration supercapacitor using PNCNFs-2-3 delivers 148 F g −1 capacitance at 1 A g −1 as well as excellent cycling stability. [ABSTRACT FROM AUTHOR]

Self-supported porous carbon nanofibers (CNFs) network has been prepared by electrospinning technology assisted with template method. The as-prepared material is rich in sub-nanoscale pores and nitrogen and oxygen functional groups, which can serve as a fast conductive network with abundant electrochemical active sites and greatly facilitates the transport of electrons and ions. When the porous CNFs network is used as an electrode for supercapacitor in a three electrode system, it displays a high capacitance of 233.1 F/g at 0.2 A/g, and a capacitance of 130.2 F/g even at 14 A/g. It maintains a capacitance of 154.0 F/g with 90.17% retention after 4000 cycles at 2 A/g. Moreover, the assembled symmetric supercapacitor not only exhibits excellent rate capability and cycle performance, but also delivers an energy density of 4.17 Wh/kg and a power density of 2500 W/kg. The experimental results demonstrate that the prepared N, O co-doped carbon nanofibers with rich sub-nanoscale pores are a promising electrode material for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

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

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]

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]

Nitrogen-doped carbon nanofiber (NDCN) was synthesized via carbonization of polypyrrole (PPy) coated bacterial cellulose (BC) composites, where BC serves as templates as well as precursor, and PPy serves as the nitrogen source. The synthesized NDCN was employed as electrode for both supercapacitors and Li-ion batteries. The large surface area exposed to electrolyte resulting from the 3D carbon networks leads to sufficient electrode/electrolyte interface and creates shorter transport paths of electrolyte ions and Li + ion. Besides, the three types of N dopants in NDCN improve the electronic conductivity, as well as superior electrochemical performance. [ABSTRACT FROM AUTHOR]

We reported the facile synthesis of hollow carbon nanofibers/MnO 2 (CNFs/MnO 2 ) composites for high performance supercapacitor electrodes. The nanocomposites were prepared via electrospinning of carbon nanofibers/MnOx and subsequent hydrothermal coating of MnO 2 nanosheets on the surface. The unique hollow structure and numerous MnO 2 nanosheets increased the contact area between the electrodes and electrolyte so that the CNFs/MnO 2 electrode exhibited higher electrochemical performance than the CNFs/MnOx composites. The CNFs/MnO 2 composites displayed a specific capacitance of 151.1 F/g at 1 A/g, and 90% of the initial specific capacitance was maintained after 8000 cycles. An asymmetric supercapacitor was assembled with the CNFs/MnO 2 composites and the active carbon. The asymmetric supercapacitor exhibited a high performance in 1 M Na 2 SO 4 aqueous solution with a working potential window ranging from 0 to 1.8 V. Furthermore, the asymmetric supercapacitor possessed a cycling stability with 93.5% capacitance retained after 1500 cycles at 1 A/g. [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]

• Hierarchical porous carbon (HPC) is obtained with three-dimensional (3D) structure. • The HPC with highly fluffy 3D continuous network is found as an ideal support. • HPC-supported MnO 2 nanofibers composite is achieved as a supercapacitor material. • The as-prepared MnO 2 @HPC composite has 3D interpenetrating network structure. • The MnO 2 @HPC composite presents excellent electrochemical performance. For improving the conductivity of porous carbon and the utilizations of its pore structures, a hierarchical porous carbon (HPC) had been developed with highly fluffy three-dimensional (3D) continuous network structure. Using the HPC as a support, a novel MnO 2 @HPC composite with 3D interpenetrating network structure was prepared as electrode material of supercapacitor via simple hydrothermal method. When the hydrothermal reaction temperature was 100°C, the MnO 2 nanofibers (∼5 nm) were uniformly grown on and within the fluffy 3D porous network of the HPC, forming a composite with interpenetrating network structure. The as-prepared composite (MnO 2 @HPC-100) exhibited the characteristics of both electric double-layer capacitance and pseudo-capacitance, which had a high specific capacity of 368 F g−1 at a current density of 0.5 A g−1 and 186 F g−1 at 10 A g−1 (50.5% retention). In addition, the asymmetric supercapacitor device was assembled with a relatively high energy density of 88.2 Wh Kg−1 at a power density of 162 W Kg−1. The device had a high capacity retention rate of 95% after 10000 cycles, and the coulomb efficiency was stable at 99.7%, showing the excellent stability of the composite. Therefore, the MnO 2 @HPC-100 composite has great application prospects in energy storage. [Display omitted] [ABSTRACT FROM AUTHOR]

Plasma-treatment carbon nanotubes (CNTs) grafted with maleic anhydride (MA) were embedded in polyacryonitrile nanofibers via electrospinning and subsequently carbonizated at 800 °C to fabricate carbon nanofibers (CNFs). The grafted degree of MA on CNTs (CNTs-MA) was determined via Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The morphology, surface composition and conductivity of the CNTs-MA/CNF were characterized using electron microscopy, X-ray photoelectron and electrochemical impedance spectroscopy, respectively. CNTs-MA not only affected the conductivity of the CNFs but also the types of the nitrogen functional groups that could be represented as active sites on the CNFs to enhance the performance of the supercapacitors. When 2.5 wt.% CNTs-MA was embedded in the CNFs, the highest conductivity was obtained at 5.2 s/cm, and the amount of pyridinic and pyrrolic species increased to 70.3%. However, the highest capacitance was not obtained with 2.5 wt.% CNTs-MA added because of current leakage present in the system. The highest capacitance was 382 F/g with 1.0 wt.% CNTs-MA embedded in CNF with proper conductivity of 2.2 s/cm. Furthermore, galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy measurements also demonstrated that 1.0 wt.% CNTs-MA embedded in CNF resulted in better electrochemical reversibility and impendence properties. [ABSTRACT FROM AUTHOR]

RuO 2 /activated carbon nanofiber (ACNF) composites containing graphene are prepared by a simple electrospinning method, followed by physical activated carbonation. We investigate the electrochemical properties as supercapacitor electrodes and the structural properties of these RuO 2 /ACNF materials as a function of the graphene concentration. The porous RuO 2 /ACNF composites exhibit an improved microstructure in terms of increased surface area, large mesopore volume fraction, and increased electrical conductivity with increasing graphene content. The RuO 2 /ACNFs with 3 wt% graphene are characterized as having a large specific surface area of up to 1552.2 m 2 g −1 , mesopore volume fraction up to 53%, high electrical conductivity of over 0.59 Scm −1 , gravimetric capacitance of 180.2 Fg −1 and energy density of 20.4–15.3 Whkg −1 over a power density range of 400–10,000 Wkg −1 in 6.0 M KOH electrolyte. These results suggest that RuO 2 /ACNF with graphene offers the benefits of low resistance for charge diffusion and a short pathway for ion transportation. Therefore, RuO 2 /ACNF with graphene shows good capacitive behavior when applied as an electrode material for supercapacitors in terms of high rate capability, large capacitance, and more efficient energy density. [ABSTRACT FROM AUTHOR]

Nanostructural carbon nanofibers are prepared through electrospinning in a precursor solution composed of polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and N,N-dimethylformamide. We investigate the effect of PMMA molecular weight on the morphology and electrochemical performance of the nanofibers. During pyrolysis, PMMA decomposition causes the nanofibers to develop from a porous structure into a hollow structure with increased PMMA molecular weight. The removal of PMMA also substantially increases the specific surface area and the pore volume of the carbon nanofibers. Electrochemical measurements reveal that the specific capacitance of the PAN/PMMA-derived carbon nanofibers with a low-molecular-weight PMMA exhibits a specific capacitance of 210 F/g, which is approximately 38% higher than that of the neat PAN-derived carbon nanofibers. Additionally, the fibers exhibit favorable cycling stability with a retention ratio of almost 100% after 2000 cycles. [ABSTRACT FROM AUTHOR]

Binder-free Ni(OH) 2 /carbon nanofiber composites used as supercapacitor electrodes were fabricated through the chemical precipitation of Ni(OH) 2 on electrospun carbon nanofibers. These composites exhibited a hierarchical structure in which Ni(OH) 2 nanoflakes connected with the carbon fiber network. We varied the annealing temperature to investigate the morphological progress and the subsequent electrochemical performance of the composite fibers. The hierarchical structure remained unchanged when the annealing temperature was lower than 300 °C. At 350 °C, most Ni(OH) 2 was converted to NiO, and NiO peeled off from the fiber surface, forming NiO microparticles. Electrochemical measurements revealed that the specific capacity of the Ni(OH) 2 /carbon nanofiber composites increased with an increase in the annealing temperature and reached a maximum of 455 C/g at 300 °C. In addition, the Ni(OH) 2 /carbon nanofiber composites exhibited a favorable cycling stability after 2000 cycles without fading. The electrochemical performance of the composites was satisfactory because of the synergetic effect of the faradaic behavior of Ni(OH) 2 and easily accessible electron transport in the carbon nanofiber network. At 350 °C, the peeling off and aggregation of NiO microparticles caused a reduction in the specific capacity of the Ni(OH) 2 /carbon nanofiber composites. [ABSTRACT FROM AUTHOR]

Hybrid nanomaterials with hierarchical structures have been considered as one kind of the most promising electrode materials for high-performance supercapacitors with high capacity and long cycle lifetime. In this work, multi-dimensional hybrid materials of nickel-cobalt layered double hydroxide (Ni-Co LDH) nanorods/nanosheets on carbon nanofibers (CNFs) were prepared by electrospinning technique combined with one-step solution co-deposition method. Carbon nanofiber membranes were obtained by electrospinning of polyacrylonitrile (PAN) followed by pre-oxidation and carbonization. The successful growth of Ni-Co LDH with different morphologies on CNF membrane by using two kinds of auxiliary agents reveals the simplicity and universality of this method. The uniform and immense growth of Ni-Co LDH on CNFs significantly improves its dispersion and distribution. Meanwhile the hierarchical structure of carbon nanofiber@nickel-cobalt layered double hydroxide nanorods/nanosheets (CNF@Ni-Co LDH NR/NS) hybrid membranes provide not only more active sites for electrochemical reaction but also more efficient pathways for electron transport. Galvanostatic charge-discharge measurements reveal high specific capacitances of 1378.2 F g −1 and 1195.4 F g −1 (based on Ni-Co LDH mass) at 1 A g −1 for CNF@Ni-Co LDH NR and CNF@Ni-Co LDH NS hybrid membranes, respectively. Moreover, cycling stabilities for both hybrid membranes are significantly enhanced compared with those of Ni-Co LDH NR and NS powders. This facile method provides a new strategy for designs and applications of binary transition metal oxides/hydroxides deposited on various substrates for next-generation energy storage devices. [ABSTRACT FROM AUTHOR]

We present a novel approach to fabricate nitrogen-enriched porous carbon nanofiber networks based on electrospinning from a poly(acrylonitrile) (PAN) solution containing allyl polyethylene glycol (APEG), followed by a thermal treatment. During the pre-oxidation process, the APEG can react with the diene systems formed by the PAN elimination reaction via a Diels-Alder addition. The grafted APEG acts as a porogen, increasing the number and enlarging the size of the micropores, and also increases the nitrogen-doping level in the carbon nanofibers. When used as a binder-free electrode for supercapacitors, the nitrogen-enriched porous carbon nanofiber films can exhibit a specific capacitance of up to 302 F g −1 at 0.2 A g −1 , retaining 94.6% of their capacitance after 2000 cycles. A power density of 10 kW kg −1 with an energy density of 5.2 Wh kg −1 can be achieved in an aqueous solution. The excellent electrochemical performance of the nanofiber films is attributed to their high specific surface area (753 m 2 g −1 ) and high nitrogen content (5.44%). [ABSTRACT FROM AUTHOR]

The demand for high-performance energy storage devices such as supercapacitors and lithium-ion batteries has been increasing to meet the application requirements of renewable energy systems. Here, high energy density aqueous asymmetric supercapacitor (ASC) is assembled based on carbon nanofibers (CNF) network positive electrode and tungsten trioxide (WO 3 ) nanorod bundles negative electrode. Polyaniline-based CNF are prepared by direct carbonization of polyaniline nanofibers. WO 3 nanorod bundles are synthesized via a simple sodium chloride assisted hydrothermal process. The CNF//WO 3 ASC device operates with a voltage of 1.6 V and achieved a high energy density of 35.3 Wh kg −1 at a power density of 314 W kg −1 . Furthermore, the device shows an excellent cycling performance with capacitance retention of 88% after 1000 cycles. [ABSTRACT FROM AUTHOR]

• Sandwich-structured C/Mn/C with a triple layer were fabricated by electrospinning. • Well-preserved MnO 2 NPs in the interlayer are utilized as electroactive sites. • Hollow core present in the interlayer serves as an excellent conductive network. • Symmetric C/Mn(10)/C electrode showed high specific capacitance and long cycle life. • Asymmetric C/Mn(10)/C offers high energy density in a high potential window. Sandwich-structured carbon nanofiber/MnO 2 /carbon nanofiber composites with a triple layer are fabricated by electrospinning. The optimized sandwich-structured composite electrodes exhibit the maximum specific capacitance of 220 F/g at 1 mA/cm2, a high energy density of 24.63 Wh/kg at a power density of 400 W/kg, and an excellent retention rate of 94% after 10,000 cycles. The stable spatial distribution of MnO 2 nanoparticles between the upper and lower carbon nanofiber webs allowed full use of the well-preserved MnO 2 nanoparticles in the interlayer as electroactive sites, providing better electrochemical performance. Furthermore, the hollow core present in the interlayer serves as an excellent conducting network, providing a short ion diffusion path for both ions and electrons. In addition, the asymmetric supercapacitor shows excellent cycling behavior between 0 and 1.4 V and a large energy density of 44.3 Wh/kg at a power density of 400 W/kg, showing great potential in the development of energy storage devices with high energy density for practical applications. [ABSTRACT FROM AUTHOR]

Fifteen microporous carbons with variable nanotextural characteristics were prepared by KOH activation through tuning the KOH/carbon ratio and activation temperature. The prepared porous carbons have a high ratio of micropores and specific surface area up to 95% and 1410 m2 g−1, respectively. Combining the pore-structure analyzes and electrochemical measurements in aqueous KOH and H 2 SO 4 electrolytes, it is shown that the complexity of the pore structure has a significant effect on the electrochemical performance. The solvated/naked K + can penetrate across the narrow pore entrance of the microporous carbons with an average pore size smaller than 0.6 nm and form electric double-layer (EDL) capacitance, while solvated/naked SO 4 2− cannot due to its larger ionic size. However, the penetration of SO 4 2− followed by hydrated H + become available when the average pore size is larger than 0.6 nm. With the combination of pseudocapacitance and EDL capacitance, microporous carbon shows a much higher supercapacitive performance in H 2 SO 4 than that in KOH electrolyte. This work on pore-structure dependence of supercapacitive performance paves a guide for tailoring pore-structure suitable for aqueous KOH and H 2 SO 4 electrolytes. [ABSTRACT FROM AUTHOR]

Highlights: [•] The interconnected carbon nanofibers were prepared by an electrospinning technique. [•] The interconnected fibers developed conductive pathways. [•] The interconnected fibers showed 24% enhancement on the specific capacitance. [•] The interconnected fibers are promising to be used as electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]

Abstract: Organic-inorganic hybrid composite carbon nanofibers (CCNFs) are prepared by one-step electrospinning and subsequent thermal treatment using polyphenylsilane (PPS) as an inorganic precursor. We investigate the structural properties and electrochemical behavior of these CCNF materials when applied as supercapacitor electrodes as a function of the carbonization temperature ranging from 800 to 1000°C. The introduction of PPS induces thermal stability for the organic-inorganic hybrid CCNFs via the incorporation of a porous structure with stabilized functional structures such as silicon oxynitride (SiOxNy) and silicon oxycarbide (SiOxCy). This phenomenon is attributed to the synergistic effect of both the double-layer capacitance and the pseudo-capacitive effect induced by the porous carbon layer and the some surface functionalities), thereby providing high charge capacity, power and energy density. [Copyright &y& Elsevier]

Abstract: Vine-like polyaniline (PANI) nanostructures were prepared using electrochemical polymerization on activated carbon nanofibers (ACNF) in order to use as a supercapacitor. Electrospun polyacrylonitrile (PAN)-based nanofibers were firstly carbonized and physically activated to increase the specific surface area. The PANI formed a vine-like shape and well-contacted with the surface of ACNF. The remarkably improved electrochemical performances of PANI-deposited ACNF electrode were investigated using cyclic voltammetry (CV) and galvanostatic charge/discharge test, and electrochemical impedance analysis. The current area of the PANI-ACNF electrode is higher than that of ACNF electrode in CV curves and the specific capacitance of the PANI-ACNF was 832Fg−1 which is much higher than 353Fg−1 of ACNF at a current density of 1Ag−1 in galvanostatic charge/discharge analysis. During galvanostatic charge/discharge test of 1000 cycles at 1Ag−1, the PANI-ACNF sample keeps its specific capacitance up to the value of 765Fg−1 (92% retention). Also, the PANI nanostructure on the ACNF substrate achieved a rapid doping/dedoping process between the surface of electrode and electrolyte ions in comparison with ACNF electrode. [Copyright &y& Elsevier]

Abstract: The vanadium pentoxide (V2O5)/carbon nanofiber composites (CNFCs) were prepared from polyacrylonitrile/V2O5 in N,N-dimethylformamide by a simple electrospinning method, and their electrochemical properties as supercapacitor electrodes were investigated. Different loadings of V2O5, the microstructures of the CNFCs (e.g., nanometer-size diameters, high specific surface areas, narrow pore size distributions, and tunable porosities) were changed, and the textural parameters significantly affected the electrochemical properties of the composites. The CNFC capacitors delivered the high specific capacitances of 150.0Fg−1 for the CNFCs in an aqueous, with promising energy densities of 18.8Whkg−1, over a power density range of 400–20,000Wkg−1. The CNFCs simultaneously exhibited excellent capacity retention. [Copyright &y& Elsevier]

Abstract: MnO2/carbon nanotubes (CNTs)–embedded carbon nanofibers (CNFs) nanocomposites (MnO2/CNTs–CNFs) have been prepared using electrospinning and in situ redox deposition technique. The as-prepared nanocomposites were directly employed as freestanding electrodes to evaluate the electrochemical properties. Results showed that the nanoscopic MnO2 deposits were incorporated uniformly into the CNTs–embedded CNFs network structure, which hold a great promise for high-performance supercapacitor applications. Compared to the pure CNFs substrate, the improved electric conductivity of CNTs–embedded CNFs substrate enabled a better utilization of MnO2 coating, thus resulting in higher specific capacitance (374F/g) and better rate capability (53.4%). Excellent capacitance retention of 94% of the initial capacitance after 1000cycles was achieved on the freestanding MnO2/CNTs–CNFs nanocomposites electrode. The specific capacitance was found to increase significantly with the increase in the electrolyte temperature, which offered an insight into the practical supercapacitor applications. [Copyright &y& Elsevier]

• High-efficiency preparation of layered SnO X nanostructure composite carbon hybrid nanofiber mats by blow-spinning. • A dual network conductive structure consisting of an upper SnOx nanostructure and underlying hybrid carbon nanofiber. • The SnO 2 nanoparticles are transformed into nanowires through autocatalysis and self-assembly without using metal catalysts or reductive atmosphere. • The SnO 2 nanowire carbon hybrid nanofibers mat electrode materials show excellent specific capacitance (~420.1 F g −1) and cycling stability (92.5% retention after 3000 cycles). Tin oxide (SnO X) nanomaterials have received attention as electrode materials due to their large theoretical capacitance, but their use remains limited due to cumbersome processing and limited electrical conductivity. In this work, SnO X nanoparticles, nanowires and nanorods embedded in a layered composite carbon hybrid nanofiber mat are prepared via blow-spinning followed by pre-oxidation and a high-temperature calcination self-assembly process in argon using stannous chloride and polyacrylonitrile as raw materials. As a result, a dual network conductive structure consisting of an upper SnOx nanostructure and underlying hybrid carbon nanofibers is created. The nanostructure morphology is controlled by reaction time through a transformation from nanoparticle to nanowire and lastly to nanorod and the potential formation and growth mechanism is discussed in detail. It is found that pre-oxidation introduces oxygen in the polyacrylonitrile that upon calcination into carbon nanofibers is released as oxygen containing gaseous substances that fuel transformation and oxidation of stannous chlorides and oxides into the self-assembled stannic oxide nanostructures in an approach applicable to other metal oxide structures. The SnO 2 nanowire carbon hybrid nanofibers mat (SnO 2 NW@CNFMs) exhibits the highest specific capacitance of 420.1 F g −1 at a scan rate of 5 mV s −1 and good cyclic stability of 92.5% capacitance retention after 3000 cycles at 1 A g −1 which exceeds the performance in earlier reported studies of tin oxide nanomaterials. The high electrochemical properties combined with the novel preparation procedure presented in this study promote SnO 2 NW@CNFMs as a good choice for electrodes in electronic appliances and electric vehicles. [Display omitted] [ABSTRACT FROM AUTHOR]

The lignin-based multi-channels carbon nanofibers (MCNFs) @ SnO 2 nanocomposites with various microstructures are synthesized via co-electrospinning by regarding Poly (vinyl pyrrolidone) (PVP)–SnCl 2 ·2H 2 O as shell materials and lignin-Poly (methyl methacrylate) (PMMA) at different mass ratios as core materials, followed by heat treatment and acid treatment. The experimental results show that when the mass ration of lignin to PMMA in the core region is 5:5, the obtained nanocomposites possess hierarchical internal channels, porous surface, and high specific surface area. This optimized nanocomposite as supercapacitor electrode shows high specific capacitance of 406 F g−1 at current density of 0.5 A g−1. In addition, the electrode exhibits unexceptionable cycling stability with only 5% capacitance decay over 10 000 cycles at 10 A g−1. Furthermore, the symmetric supercapacitor using the optimized nanocomposites as electrodes possesses remarkable power and energy densities. The superior electrochemical performance of nanocomposites is benefited from the hierarchical structures of MCNFs, faradaic pseudocapacitance of SnO 2 , and pore-forming effect of SnCl 2 ·2H 2 O. The unique hierarchical nanocomposites show great potential in future development of lignin-based low-cost, non-toxic and eco-friendly carbon materials for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

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

It is very challenging for carbon materials to gain high volumetric capacitance (C v) without sacrificing gravimetric capacitance (C g) as well as high rate and cycling performances to meet requirements for supercapacitors with limited space. Here, B/P/N/O co-doped hierarchical porous carbon nanofiber self-standing film was fabricated by a facile electrospinning and one-step carbonization/activation method using polyacrylonitrile solution containing boric acid and phosphoric acid. The optimized BPNOCNF-45 has high content (24.65 at.%) of heteroatoms, especially the highest content (12.93 at.%) of active heteroatom species (N-5, N-6, B–C, O–I, P2 and P3), high bulk density (1.19 g cm−3), high meso-/macropore ratio (70%), low charge transfer and ion diffusion resistance. These contribute to its prominent C v (395 F cm−3 at 1 A g−1) while maintaining high C g (332 F g−1) and excellent rate performance in KOH electrolyte. By comparison, the assembled symmetric supercapacitor in Na 2 SO 4 electrolyte delivers remarkably higher volumetric/gravimetric energy densities (21.1 Wh L−1 at 523.5 W L−1, 17.7 Wh kg−1 at 439.9 W kg−1) and capacitance retention of 90% after 10000 cycles. Furthermore, the assembled flexible supercapacitor also shows excellent capacitance performances. Such a densely co-doped porous carbon nanofiber film has great potential for applications in compact and miniaturized supercapacitors. Image 1 • Functional molecules were used to prepare B/P/N/O co-doped carbon nanofiber film. • It displays high active heteroatom content, high meso/macropore ratio and bulk density. • It exhibits prominent volumetric capacitance and high gravimetric capacitance. • Symmetrical and flexible supercapacitors show excellent energy storage performances. [ABSTRACT FROM AUTHOR]

By exploiting the facile advantages of the electrospinning process, we decorated NiCo-based bimetallic oxide nanoparticles with a tunable stoichiometric ratio onto carbon nanofibers (CNFs) and subsequently heat-treated them as an electrode assembly. The bimetallic loading density on the fibrous network was ∼32 wt%, and the Ni:Co stoichiometric ratio was varied; the high-Ni-loaded (Ni 40 :Co 20) nanofibrous electrode showed a specific capacity of 80.2C g−1 at a current density of 1 A g−1, and the specific capacity increased to 165.6C g−1 when the Co loading was increased to Ni 20 :Co 40. CNFs embedded with NiCo bimetallic oxide-based electrode showed 84.3% capacity retention even after cycling at 10 A g−1. The Co-rich electrode assemblies presented excellent cyclic stability of 94.9% capacity retention after 3000 cycles at 5 A g−1 and excellent rate capability and low internal charge resistance. The all-solid-state asymmetric supercapacitor of the C–NiCoO NFs//activated carbon device exhibited a cell specific capacitance of 191.4 F g−1 at a current density of 1 A g−1 in the potential window from 0 to 1.6 V and exhibited a maximum energy density of 67.9 W h kg−1. Surface-embedded Ni x Co y O 4 nanoparticles on CNFs exhibited superior electrochemical properties because of the uniform monodispersive nanograin network over the carbon fibrous conductive surface and the effective reversible redox reaction ability of the bimetallic sites. The thin-layered graphite features of the bimetallic nanograins improved their electrical conductivity and prevented aggregation of the nanoparticles, thereby promoting cyclic stability and avoiding leaching from the carbon fibrous surface. Image 1 [ABSTRACT FROM AUTHOR]

A novel facile and scalable strategy is developed to prepare a hierarchical porous nonwoven of hollow N-doped carbon nanofibers embedded with graphene nanosheets (HN-CNFs/GNs) as an integrated electrode for flexible all-solid-state supercapacitors. It was found that graphene nanosheets (GNs) were curled inside the electrospun fibers, but freely expanded and connected adjacent CNFs in the form of nanosheets after carbonization, thereby increasing the electrochemical capacitance interface and conductivity as well. When the weight ratio of GNs is 2 wt%, the HN-CNFs/GNs delivers high capacitance of 249 F g − 1 at 1 A g − 1 in a three-electrode configuration. A two-electrode symmetrical cell delivers extraordinary cycling stability with no capacitance degradation after 5000 cycles. The symmetric all-solid-state supercapacitor provides a remarkable cycling stability with a capacity retention of 90% after 2000 cycles and high rate capacity. The device also displays outstanding flexibility with no obvious capacitance decay even when bent to 180°. This research proves the potential application of the nonwoven of HN-CNFs/GNs in high efficient, wearable and flexible energy storage devices. Image 1 • A hierarchical porous nonwoven of hollow N-doped carbon nanofibers embedded with graphene nanosheets (HN-CNFs/GNs) was sythesized by a one-step method. • Graphene nanosheets (GNs) were found to be curled inside the electrospun fibers, but freely expanded and connected adjacent CNFs in the form of nanosheets after carbonization, thereby increasing the electrochemical capacitance interface. • The particular characteristics of the HN-CNFs/GNs, such as N-doping, hierarchical porosity and hollow fibers, providing a high specific capacitance (249 F g − 1 at a current density of 1 A g − 1 in three-electrode system), excellent cycle stability (99% retention of 5000 cycles in symmetric two-electrode system) and outstanding flexibility (no obvious decay when bending to 180° in all-solid-state device) when the adding ratio of GNs is 2 wt%. [ABSTRACT FROM AUTHOR]

The present work reports an organic molecule electrode (OME) based on the graphene and graphene nanomesh (GNM) hydrogel non-covalently functionalized by caffeic acid (CFA) molecules (denoted as G&GMH-CFA). In such electrode system, the three-dimensional conductive network has a cross-linking channel constructed by means of the in-plane pores on the graphene nanomesh, which is benefit for exposing more active sites accessible to electrolyte and accordingly enhancing supercapacitive behaviors of the OME. The G&GMH-CFA delivers a specific capacitance of 482.6 F g−1 at current density of 1 A g−1. And it is noted that the Faraday current response peaks are located in the positive potential range of 0.6 V, which is superior to the organic molecules electrode reported in the correlative works. In addition, the density functional theory (DFT) calculations are used to illuminate the core issue of charge storage mechanism and binding interactions between CFA and graphene. To match with the resultant positive electrode, AQ functionalize graphene-like nanoflower (CNF-AQ) was prepared as counterpart (negative) electrode. The assembled asymmetric supercapacitors (ASC) CNF-AQ//G&GMH-CFA2 could exhaustively release the supercapacitive performance due to match and self-coordination based on the reasonable matching of two electrodes in structure, charge quantity and kinetics during the electrochemical energy storage process. The CNF-AQ//G&GMH-CFA2 delivered energy density of 26.4 Wh kg−1 at the power density of 0.7 kW kg−1. Two tandem CNF-AQ//G&GMH-CFA2 devices could easily light 88 LEDs. The organic molecule electrode is fabricated by the CFA functionalized graphene hydrogel with plentiful transport channels inside of the conductive skeleton, matching with CNF-AQ to assemble full-carbon ASC could easily light 88 LEDs. Image 1 [ABSTRACT FROM AUTHOR]

A hierarchical structure is proved to be important for the improvement of electrochemical performances of MnO 2 -based electrode materials used in supercapacitors. However, the rational design of materials' structure and its real performance served as electrode materials are still facing challenges. Herein, hierarchical porous carbon nanofibers using ZIF-8 nanoparticles as pore templates are designed to provide one-dimensional hollow frameworks for the growth of ultrathin MnO 2 nanosheets (referred as HPCNF/MnO 2). The as-prepared HPCNF/MnO 2 samples have a hierarchical coaxial core-shell structure, with HPCNFs as the core and MnO 2 sheets as the shell. The novel nanostructure of this hybrid provides abundant electrochemical active sites for Faradic reactions and short diffusion channels for ions/electron transport. The utilization of HPCNF/MnO 2 active material with such a structure can be significantly enhanced, especially at the high current density. When evaluated as electrode materials, HPCNF/MnO 2 exhibits a specific capacitance of 269 F g−1 at 0.5 A g−1 (308 F g−1 for MnO 2), a high capacitive retention of 98% even after 5000 cycles at 50 mV s−1 by cyclic voltammetry (86.7% capacitance retention at 1 A g−1 after 2000 cycles) and a rate capability of 58% from 0.5 to 10 A g−1. Especially at the current density of 10 A g−1, the specific capacitance of HPCNF/MnO 2 has increased by 133% compared with that of non-porous carbon fiber/MnO 2 composites, demonstrating a great superiority of hierarchical porous carbon nanofibers as frameworks to support pseudocapacitive materials. [ABSTRACT FROM AUTHOR]