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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]

[Display omitted] • 1D skin-core multilayer structure was fabricated by a facile template method. • Bicontinuous electron/ion transport during the charge/discharge process. • The large specific surface area and hollow hierarchical porous structure. • Adjusting active layers or sites can obviously improve the capacitive properties. • The maximum energy density of 8.77 Wh kg−1 at a power density of 0.25 kW kg−1. The fast transport of electrons and ions within electrodes is crucial to the final electrochemical properties. Herein, we have developed a unique ultra-long one-dimensional (1D) skin-core multilayer structure based on electrospun carbon nanofibers mainly through a facile Stöber method combined with resorcinol–formaldehyde resin, which not only achieves bicontinuous electron/ion transport during the charge/discharge process, but also provides large surface area for ion adsorption. Particularly, controlling the number of active layers as well as regulating the active sites in layer both can obviously improve capacitive properties. Benefiting from the synergistic effects of the desirable architecture, such the rational-designed skin-core structural carbon nanofibers as supercapacitor electrode can deliver a high specific capacitance up to 255 F g−1 at 0.5 A g−1, favorable rate capability with 89% capacitance retention of initial capacitance at 8 A g−1, and excellent cycling stability with nearly 93% capacity retention after 10,000 cycles at 2 A g−1. Furthermore, the as-assembled symmetric supercapacitor devices also present a maximum energy density of 8.77 Wh kg−1 at 0.25 kW kg−1 and a maximum power density of 3.70 kW kg−1 at 6.74 Wh kg−1. Such skin-core carbon nanofibers provide an effective strategy to design high-performance supercapacitor electrode for the next-generation energy storage devices. [ABSTRACT FROM AUTHOR]

Herein, MnO2 nanoflowers are electrodeposited on a self-supported and electroconductive electrode in which 2D Ti3C2Tx nanosheets are encased in carbon nanofibers (MnO2@Ti3C2Tx/CNFs). This improves the conductivity and hydrophilicity of the MnO2 composite electrode. The asymmetric supercapacitor shows a high energy density of 46.4 W h kg−1 and a power density of 4 kW kg−1. [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]

Highly graphitic porous carbon was derived from kelp biomass and prepared using KOH as the main activating agent with K2FeO4 as the assisting activated agent for supercapacitor applications. The optimum K2FeO4 mass in the total activating agent and temperature were investigated. The characterization results showed porous sheet carbon with a high specific surface area of 2868 m2 g−1 and a low ID/IG of 0.909. It delivered an excellent specific capacitance of 438 F g−1 at 0.5 A g−1. In addition, the assembled supercapacitor device reached the highest energy density of 19.9 W h kg−1 with a power density of 398 W kg−1. [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]

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]

It is difficult for green sustainable lignin-based materials to simultaneously obtain efficient electromagnetic wave absorption (EMWA) and supercapacitive energy storage (SCES), which has not yet been reported. Herein, the light-weight lignin-based carbon nanofibers (LCNFs) with proper pore size, well graphitization degree, and heteroatom doping were tailored through electrospinning and carbonization processes. Interestingly, the graphitization degree and porous structure of LCNFs could be easily adjusted by changing the activating temperature, and the higher conductivity was achieved for preparing LCNFs at higher activating temperature due to the differences in the crystal size and activating degree of LCNFs. As a result, in the field of EMWA, the LCNFs-950 exhibited the minimum reflection loss (RL) value was −41.4 dB and the absorbing frequency was 9.05 GHz at 2.5 mm thickness, which meant this absorbent could absorb and/or dissipate more than 99.9% of incident electromagnetic wave (EMW). Furthermore, the LCNFs-950 also exhibited excellent SCES ability. In two-electrode system, the optimal LCNFs-950 symmetric supercapacitor specific capacitance reached 139.4 F/g at a current density of 0.5 A/g, meanwhile, the energy density was 41.4 Wh/kg at a power density of 3500 W/Kg. These multifunctional features of LCNFs will be highly promising for the next-generation environmental remediating materials. [Display omitted] • Increasing the activating temperature was an effective strategy for preparing renewable and low-cost multifunction LCNFs. • Multifunction LCNFs in both electromagnetic wave absorption and electrochemical energy storage were fabricated. • The minimum reflection loss was −41.4 dB and the absorbing frequency was 9.05 GHz at 2.5 mm thickness. • The specific capacitance, energy density and power density were up to 139.4 F/g, 41.4 Wh/kg and 3500 W/Kg, respectively. [ABSTRACT FROM AUTHOR]

Thin carbon nanofibers (TCNFs) hanging on branched carbon nanofibers (3D TCNF/CNF) with an N-doping level up to 8.7 at% for high-performance supercapacitors are designed and synthesized. TCNF/CNF shows a 3D hierarchical porous structure, a large surface area, abundant ionic-channels, and a great number of electrochemically active sites by N-doping. Because of the multiple synergistic effects of these features, the supercapacitors (SCs) based on TCNF/CNF show a remarkably excellent electrochemical behavior with a high specific capacitance of 224 F g−1. After 50 000 cycles of charge/discharge, 92% of the initial capacitance value is retained in 1.0 M H2SO4 electrolyte. Moreover, the TCNF/CNF-based SCs show low internal resistance, leading to a high power density with a relatively high energy density. [ABSTRACT FROM AUTHOR]

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

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 increasing commercialization of flexible electronic products has sparked a rising interest in flexible wearable energy storage devices. Supercapacitors are positioned as one of the systems with the most potential due to their distinctive advantages: high power density, rapid charge and discharge rates, and long cycle life. However, electrode materials face challenges in providing excellent mechanical strength while ensuring sufficient energy density. This study presents a method for constructing a flexible composite electrode material with high capacitance and mechanical performance by electrochemically depositing high-quality manganese dioxide (MnO 2) onto the surface of a nanocellulose (CNF) and carbon nanotube (CNT) conductive film. In this electrode material, the CNF/CNT composite film serves as a flexible conductive substrate, offering excellent mechanical properties (modulus of 3.3 GPa), conductivity (55 S/cm), and numerous active sites. Furthermore, at the interface between MnO 2 and the CNF/CNT substrate, C-O-Mn bonds are formed, promoting a tight connection between the composite materials. The assembled symmetric flexible supercapacitor (FSC) demonstrates impressive performance, with an areal specific capacitance of 934 mF/cm2, an energy density of 43.10 Wh/kg, a power density of 166.67 W/kg and a long cycle life (85 % Capacitance retention after 10,000 cycles), suggesting that they hold promise for FSC applications. [Display omitted] [ABSTRACT FROM AUTHOR]

We report the microstructure, electrical and electrochemical properties of hybrid nanofibers composed of polyacrylonitrile (PAN)/lignin-derived carbon nanofibers and LaMnO3-based inorganic nanofibers for advanced applications as free-standing and binder-free electrode materials of energy storage devices. For this purpose, hybrid nanofibers are fabricated via dual-electrospinning technique and following heat-treatment at different temperatures of 700–1000 °C for simultaneous carbonization and calcination. The SEM, EDS, and XPS analyses reveal that the carbon content in the hybrid nanofibers increases with increasing the heat-treatment temperature and that La and Mn elements are dispersed uniformly over the hybrid nanofibers. The hybrid nanofibers heat-treated at 900 and 1000 °C have a high electrical conductivity of ~ 0.22 S/cm and ~ 0.35 S/cm, respectively. Accordingly, a symmetric two-electrode supercapacitor based on hybrid nanofibers heat-treated at 1000 °C is characterized to have excellent electrochemical performance such as specific capacitance of ~ 95.2 F/g at 1 A/g, power density of 667 W/kg, energy density of 17.6 Wh/kg, and capacitance retention of ~ 97% after 2000 cycles. The results denote that PAN/lignin and LaMnO3-based hybrid nanofibers can be utilized as self-supporting high-performance electrode materials for advanced energy storage devices. [ABSTRACT FROM AUTHOR]

The N‐doped porous carbon (NPC) /carbon micro‐nanotubes (CMNT) /NixCoyOz nanosheets with rich mesopores and 1.37 wt% nitrogen doping are successfully synthesized by a pyrolysis‐ionization‐precipitation combination process, using coal‐based polyaniline and nickelocene as original materials. Therein, most of the CMNT are upright CMTs and worm‐like curved CNTs, and a few are bamboo‐like tubes or carbon nanofibers. Moreover, many flower‐like aggregates assembled by spinel NiCo2O4 nanosheets are anchored on the surface of the NPC and CMNT. The NPC/CMNT/NixCoyOz exhibits a high specific capacitance and cycling stability, attributed to the large BET specific surface area (485 m2/g), suitable BET average pore size (2.3 nm), good hydrophilicity and wettability, and synergistic effects among three components. The assembled NPC/CMNT/NixCoyOz//AC asymmetric supercapacitor also demonstres a high specific capacitance of 120 F g−1 at a current density of 1 A g−1 and a high energy density of 16.7 Wh kg−1 at a power density of 500 W kg−1. [ABSTRACT FROM AUTHOR]

Herein, this paper reports a facile method to prepare electrospun carbon nanofiber mats (ECNFMs) with high specific surface area and interconnected structure using polyacrylonitrile (PAN) as a precursor and novolac resin (NOC) as a polymer sacrificial pore‐making agent. Without additional treatment, the prepared ECNFMs have a highly porous structure because NOC decomposes in a wider temperature range than most polymer activators. The NOC content in the PAN nanofibers shows important effects on porosity. The BET specific surface area of ECNFMs reaches a maximum of 1468 m2 g−1 when the precursor nanofibers contained 30 wt% NOC (ECNFM‐3) after carbonization at 1000 °C. The supercapacitor device from ECNFM‐3 electrode and all‐solid‐state electrolyte shows excellent cycling durability and high specific capacitance: ≈99.72% capacitance retention after 10 000 charge/discharge cycles and ≈320 mF cm−2 at 0.25 mA cm−2. Furthermore, it shows a large energy density of ≈11.1 μWh cm−2 under the power density of 500 mW m−2. Activation of carbon nanofibers simply by the addition of NOC into precursor nanofibers can offer a handy way to prepare ECNFMs for high‐performance all‐solid‐state supercapacitors and other potential applications. [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]

Lithium-ion supercapacitors (LICs) have received widespread interests because of their high power density, high energy and long life characteristics. The electrodes for LICs play a significant role in enhancing their performance. Therefore, it is of great significance to design and develop high-performance electrode materials for LIC through integrating various materials to make up for each other's disadvantages. Herein, a bimetallic composite nanomaterial with hierarchical structures (CoSn X /CNFM) and a porous carbon nanomaterial with high specific surface area (PCNFM) were obtained through combining electrospinning, anion exchange or alkali etching and subsequent high-temperature carbonization, respectively. The LIC assembled with the pre-lithiated CoSn X /CNFM as anode and the PCNFM as cathode exhibited a high energy density of 41.48 Wh/kg at a power density of 1500 W/kg, and still had an energy density of 28.13 Wh/kg at a high power density of 7500 W/kg, illustrating its high power density and high energy density. Thus, this paper proposes an effective method for designing and manufacturing high-performance LICs. • Nanofibers with uniformly distributed ZIF-67 NPs were prepared in batches by EMAI. • Hierarchical-structured CoSn X /CNFM was prepared by anion exchange and carbonization. • PCNFM with high specific surface area was prepared by etching and carbonization. • A LIC with pre-lithiated CoSn X /CNFM as anode and PCNFM as cathode was assembled. • The assembled LIC had high power density and high energy density. [ABSTRACT FROM AUTHOR]

SnS is an ideal material for supercapacitors because of its unique layered structure and excellent electrochemical performance, but the research of SnS based electrode materials of flexible self-supporting supercapacitors has been rarely exploited. In this study, microsphere like Co doped SnS grown on carbon nanofibers (Co-SnS@CNF) was prepared by electrospinning, hydrothermal method and annealing treatment. Co-SnS@CNF has great flexibility, high specific capacitance, excellent rate performance and cycle stability. Specifically, the specific capacitance is 750 F g−1 at the current density of 1 A g−1. The special microsphere structure with more electrochemical active sites and lower resistance of ion and charge transfer by Co doping are responsible for the superior electrochemical performances. Furthermore, when assembled Co-SnS@CNF as the symmetrical supercapacitor device, the energy density of 20.89 Wh Kg−1 and the power density of 376 W Kg−1 are achieved at the current density of 1 A g−1, while showing ultra-high cycle stability. Therefore, the Co-SnS@CNF offers excellent application potential for flexible self-supporting supercapacitors. • Revealing reasons for the high-performance of the microspherical Co-doped SnS. • The specific capacitance is 750 F g−1 at the current density of 1 A g−1. • The assembled symmetrical device exhibits the ultra-high cycle stability. [ABSTRACT FROM AUTHOR]

The dramatic development of wearable electronics has led to extensive research into flexible supercapacitors as wearable energy storage devices. The practical application of supercapacitors to wearable electronics requires improved temperature tolerance and high energy density. Herein, we report the fabrication of a high-voltage flexible aqueous supercapacitor featuring high energy density and a wide operating temperature range. This is achieved by the strategy of simultaneously utilizing asymmetric electrodes and water-in-salt gel electrolyte (WISGE). Using NaClO 4 -based WISGE and asymmetric electrodes consisting of Na-inserted MnO 2 and N-doped carbon nanofibers, we obtain excellent electrochemical performance, including a gravimetric capacitance of 97.2 F g−1, energy density of 90 Wh kg−1, power density of 28.1 kW kg−1, operation voltage window of 2.6 V, and capacitance retention of 85.2% over 10,000 charge/discharge cycles. The fabricated flexible supercapacitor is stable under repeated temperature changes between − 20 and 80 °C, regardless of bending deformation. After three cycles of cooling and heating, the initial capacitance at room temperature is 95.1% recovered. This study demonstrates the potential application of our high-performance flexible aqueous supercapacitors to wearable devices, given their resistance to changes in environmental temperature and mechanical deformation. [Display omitted] • Supercapacitor consists of the asymmetric electrode and water-in-salt gel electrolyte. • Supercapacitor exhibits wide voltage window (2.6 V) and temperature range (−20 to 80 ℃). • The initial performance was maintained even after repeated temperature changes. • Performance is stable under repeated bending deformation over wide temperature ranges. [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]

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]

In this paper, we proposed the synthesis of CoFe nanoparticles (NPs) which have been deposited on carbon nanofibers (CNFs) with a facile electrospinning route followed by thermal reduction. The performance of obtained CNF supercapacitors are improved from 51 to 190 F/g (247 mF/cm2) at 0.5 A/g with the combination of CoFe NPs and graphitized carbon layers The device possessed an energy and power density of 6.6 Wh/kg and 125 W/kg, respectively. Furthermore, the capacitance retention can still maintain about 96.6% after 10,000 cycle test and it is worth noting that the cycling stability is ultrahigh. This research proves that bimetallic nanoparticles embedded in CNFs can elucidate new insights into the development new nanofiber electrode materials for the next generation of symmetric supercapacitors. [ABSTRACT FROM AUTHOR]

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

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

Carbon nanofiber (CNF)‐based supercapacitors have promising applications in the field of energy storage. It is desirable, but remains challenging, to develop CNF electrode materials with large specific surface area (SSA), high specific capacitance (SC), and high power density, as well as excellent cycling stability and high reliability. Herein, acrylonitrile–acrylic acid copolymer P(AN‐co‐AA) was synthesized for the preparation of nitrogen‐doped microporous CNFs. Thermal degradation of the AA segment leads to the formation of micropores that are distributed not only on the CNF surface, but also inside the material. The microporous structure and nitrogen content can be manipulated at the molecular level by adjusting the weight ratio between AN and AA, and the SSA and SC could reach as high as 1099 m2 g−1 and 156 F g−1, respectively. After KOH activation, the activated CNFs have an extremely high SSA of 2117 m2 g−1 and SC of 320 F g−1, which are among the highest values ever reported for electric double‐layer supercapacitors with an alkaline electrolyte. Furthermore, the capacitance retention, which can be maintained at 99 % even after 16 000 cyclic tests, reveals outstanding durability and repeatability. [ABSTRACT FROM AUTHOR]

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

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]

[Display omitted] • The active sites-rich Ni-Co-P@C/Ni-B material enables fast transfer of electron/ion. • DFT results verify stable OH* adsorption energy and metallic nature of the hybrid. • The Ni-Co-P@C/Ni-B shows a high specific capacity of 306 mAh g−1 at 3 mA cm−2. • Highly porous N-doped C nanofibers with nanocages was made as negative electrode. • The hybrid supercapacitor device shows 68.3 Wh kg−1 energy density at 472 W kg−1. In recent times, a lot of research effort has been performed to develop hybrid supercapacitors (HSCs) because of their ability to produce high energy density as well as superb power density. The key issue for realizing high-performance HSCs is to minimize the kinetic mismatch between rapid capacitor-type anode and sluggish battery-type cathode. Optimizing the interface, morphology and microstructure of the electrode material is a favorable approach to surmount kinetic imbalance. Herein, a core–shell nanoarrays of ultrathin carbon layer-coated crystalline Ni-Co-phosphide (Ni-Co-P@C) and amorphous Ni-boride (Ni-B) is fabricated on a nickel foam substrate as a positive electrode material (Ni-Co-P@C/Ni-B). Theoretical analyses validate the best metallic characteristic and most stable OH* absorption energy for Ni-Co-P@C/Ni-B, which enhance its charge storage performance than analogous Ni-Co-P and Ni-Co-P/Ni-B. The porous nitrogen (N)-doped carbon (C) nanofibers consisting of tightly embedded metal–organic framework (ZIF-8)-derived interconnected N-C nanocages (HP-N-CFs) showed excellent charge storage kinetics as a negative electrode. The battery-type Ni-Co-P@C/Ni-B electrode revealed a specific capacity of 306.2 mA h g−1 at 3 mA cm−2, while highly porous capacitive HP-N-CFs electrode showed the highest capacity of 56 mA h g−1 at 2.5 mA cm−2. In addition, the assembled quasi-solid-state (Ni-Co-P@C/Ni-B//HP-N-CFs) HSCs exhibited the highest energy density of 68.3 W h kg−1 at a power density of 472 W kg−1 with a superb rate capability (68% at 50 mA cm−2) and decent cyclic durability (90% retention over 10,000 cycles). [ABSTRACT FROM AUTHOR]

Here, core-shell supercapacitor electrodes with high performance were prepared using electrospinning, carbonation, nitrogen-doping and chemical polymerization. The core of the electrode was a N-doped porous carbon nanofiber skeleton, its shell was a conductive polymer loaded on it. The effects of pore-forming agent content, N-doped amount, and polymerization temperature on the morphologies, structures and electrochemical performance of products in each stage were characterized, and the optimum parameters were obtained. As a freestanding electrode, the SC of core-shell composite reached 342.13 F g−1 at 1 A g−1, and its SC attenuation was only 4.6 % after 1000 cycles, indicating its good charge storage performance and cycle stability. Then a symmetric supercapacitor fabricated with the best electrode displayed an energy density of 3.10 Wh kg−1 at a power density of 50 W kg−1. Therefore, this paper proposed an effective method for developing multifunctional electrode materials of supercapacitors. [Display omitted] • A core-shell composite for high-performance supercapacitor electrode was prepared. • The core layer of the composite was the N-doped porous carbon nanofiber skeleton. • The shell layer of the composite was the polypyrrole loaded on the skeleton. • The core-shell composite electrode showed excellent electrochemical performances. • An asymmetric supercapacitor device was fabricated using the core-shell electrode. [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]

[Display omitted] • Mn-doped PAN nanofibers were decorated with ZIF-67. • Oriented attachment of PVP/ZIF-67 occurred on Mn-doped PAN-2MI nanofibers. • PVP/ZIF-67/Mn-fibers carbonized at 900 ℃ resulted in flexible C/Co-CoO x /Mn-CNF. • The areal capacitance of 1263 mF·cm−2 was obtained at a current density of 0.25 mA·cm−2. • The energy density of 0.18 mWh·cm−2 was obtained at a power density of 0.5 mW·cm−2. Electrodes for flexible supercapacitors were fabricated from manganese-doped carbon nanofibers (Mn-CNF) decorated with carbon-coated Co-CoO x (C/Co-CoO x) nanotubes. The Mn-doped polyacrylonitrile (PAN)–2-methylimidazole (2MI) solution was electrospun using optimized Mn concentrations and ZIF-67 was then surface loaded by wet impregnation with added polyvinylpyrrolidone (PVP). These ZIF-67 loaded Mn-fibers, when annealed, resulted in carbon-coated C/Co-CoO x nanotubes on the Mn-CNF surface. In the presence of PVP, ZIF-67 oriented attachment occurs, forming evenly dispersed CoO x particles even after high temperature annealing. XRD spectra exhibit the formation of metallic Co nanoparticles (NPs), whereas Raman spectra and XPS indicate Co particle oxidation. A carbon coating limits the oxidation of Co; thus, the particles are called C/Co-CoO x. A symmetric supercapacitor cell prepared using the CNFs decorated with C/Co-CoO x using an aqueous electrolyte has a capacitance of 1263 mF⋅cm−2 at a current density of 0.25 mA⋅cm−2 and a wide potential window of 1.4 V for the optimal case. Long-term cycling showed 110 % capacitance retention after 10,000 cycles. Moreover, bending tests and powering LEDs demonstrated the flexibility and improved charge storage of the prepared nanofiber electrodes. [ABSTRACT FROM AUTHOR]

Low-cost, high-performance electrodes are highly attractive for practical supercapacitor applications. MnO 2 -deposited carbon nanofiber mats (MnO 2 -CNFMs) are prepared for use as binder-free supercapacitor electrodes. MnO 2 is deposited on the mats in situ by hydrothermally decomposing aqueous KMnO 4 , leading to the formation of nanocrystals of MnO 2 . The MnO 2 -CNFM electrode produced with 38.0 μmol KMnO 4 (this electrode) shows a high specific capacitance of ~171.6 F·g −1 at a scan rate of 5 mV·s −1 . Moreover, a symmetric supercapacitor with the electrode exhibits a specific capacitance of 67.0 F·g −1 , an energy density of 6.0 Wh·kg −1 and a power density of 160 W·kg −1 at a special current of 0.1 A·g −1 . Further, the symmetric supercapacitor displays excellent cycling stability, retains approximately 99% of the capacitance after 1000 cycles. The simplicity and ease of preparation of the MnO 2 -CNFMs as well as their suitability for use in coin-type supercapacitor cells make them ideal for application in cost-effective and high-performance electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ incorporation of MnO in the CNF matrix using unique two-step carbonization. • MnO dispersed CNFs show high specific capacitance of 246F g−1 at 0.5 A g−1. • High power density of 5000 W kg−1 (8.7 W h kg−1) was achieved with 97.5 % capacitance retention after 10,000 cycles. Manganese oxides have attracted great interest as promising pseudocapacitive materials due to its low cost, variable oxidation states, and high theoretical capacitance. In this work, we report the in-situ synthesis of MnO-dispersed carbon nanofibers (CNFs) using electrospinning and a unique two-step carbonization technique. While the single-step carbonization resulted in mixed Mn x O y forms, however, by employing a suitable and optimized two-step carbonization, we were able to obtain CNFs assimilated with MnO nanoparticles (MnO-CNFs). The synthesized MnO-CNF electrodes achieved a high specific capacitance of 246 F g−1 at 0.5 A g−1 in a three-electrode system. A symmetric supercapacitor device assembled with these electrodes exhibited remarkable electrochemical performance with a maximum power density of 5000 W kg−1, maximum energy density of 14 W h kg−1, and an excellent cycling stability (97.5% retention after 10,000 cycles). The exceptional electrochemical performance of MnO-CNFs makes them promising electrode materials for practical energy storage applications. [ABSTRACT FROM AUTHOR]

A green electrode material with dual conductive networks via electrospinning with carbonization and co-precipitation method is constructed. Nitrogen-based carbon nanofiber network (CCP-N) is used as the inner-conductive, electrochemical-active substrate and flexible skeleton. The Co Ni layered double hydroxide (Co Ni LDH) nanosheets and flower-like nanospheres, which randomly and closely covering the surface of CCP-N, respectively, just as the fungus grow on trunks in nature, is regarded as outer-conductive and active substance collector in order to provide abundant active centers, sufficient reaction interface to advance fast electrolyte ions diffusion and electrons transport. Furthermore, the growth process of Co Ni LDH on CCP-N is observed by controlling growth time and the Co/Ni ratio of the precursor solution. It is found that the optimal Co/Ni ratio was 2:1, while that optimal growth time is 12 h. The specific capacitance of Co Ni LDH@CCP-N electrode reaches 1319.4 F g-1 at 1 A g-1. The assembled asymmetric supercapacitor device (CCP-N @ Co Ni LDH//CCP-N) possesses a high energy density of 48.1 W h kg-1 at power density of 576.8 W kg-1, excellent cycling stability of 82.2% retention after 10,000 cycles. The results clearly indicate the Co Ni LDH@CCP-N materials have enormously potential in energy storage. This work puts forward a novel strategy for the design and fabrication of green and advanced supercapacitors materials with high power density and energy density. [Display omitted] • A dual conductive network is established by electrospinning and co-precipitation. • CCP-N is the inner-conductive and Co Ni LDH nanosheets is the outer-conductive. • The CCP-N @ Co Ni LDH exists multifunctional charge storage principles. • The CCP-N @ Co Ni LDH possesses abundant active sites and high specific surface area. • The CCP-N @ Co Ni LDH//CCP-N delivers excellent energy density and power density. [ABSTRACT FROM AUTHOR]

In this article, vanadium nitride quantum dot/nitrogen-doped microporous carbon nanofibers (VNQD/CNF) is developed by a method of combination of electrostatic spinning and high-temperature calcination under the atmosphere of NH 3 : N 2 = 3: 2 for high performance supercapacitors. VNQD dispersing into CNF, enrichment of N atom doped in carbon bulk, and abundant porous structure not only prevent the growth and aggregation of VN nanoparticles, improve electrical conductivity, wettability, and stability of the electrode materials, but also enhance fast migration of electrolyte ions during the electrochemical process. Thus, VNQD/CNF exhibits a high specific capacitance of 406.5 F g −1 at 0.5 A g −1 and a good rate capability with a capacitance retention of 75.1% at 5.0 A g −1 . Additionally, VNQD/CNF as a negative electrode are combined with Ni(OH) 2 as a positive electrode to fabricate the hybrid supercapacitor of VNQD/CNF//Ni(OH) 2 . Remarkably, at a power density of 774.6 W kg −1 , the supercapacitor device delivers an ultrahigh energy density of 31.2 Wh kg −1 . [ABSTRACT FROM AUTHOR]

Carbon nanomaterials such as carbon nanotubes, carbon nanofibers, and graphene are exploited extensively due to their unique electrical, mechanical, and thermal properties and recently investigated for energy storage application (supercapacitor) due to additional high specific surface area and chemical inertness properties. The supercapacitor is an energy storage device which, in addition to long cycle life (one million), can give energy density higher than parallel plate capacitor and power density higher than battery. In this paper, carbon nanomaterials and their composites are reviewed for prospective use as electrodes for supercapacitor. Moreover, different physical and chemical treatments on these nanomaterials which can potentially enhance the capacitance are also reviewed. [ABSTRACT FROM AUTHOR]

In view of the current problem that MOFs (Metal-organic frameworks)-based carbon as electrode materials for supercapacitors have poor conductivity and single component. We design porous hybrid carbon nanofibers (C-ZIF-67 @PAN@ZIF-8) derived from 1D core-shell MOFs. They can combine the advantages of 1D carbon materials (high conductivity) with hybrid carbon materials (multiple components) showing excellent electrochemical performance. The specific capacitance can reach 320.8 F g−1 at a current density of 1 A g−1, which is higher than C-ZIF-8 (180.8 F g−1) and C-ZIF-8 @PAN (273.7 F g−1) in a three-electrode system. In addition, symmetrical supercapacitors are assembled with C-ZIF-67 @PAN@ZIF-8, which can provide very stable performance and almost no capacitance decay after 10,000 cycles at a current density of 5 A g−1. The supercapacitors also can offer a high energy density of 8.0 wh kg−1 at a power density of 250 w kg−1. [Display omitted] • A new and highly efficient design of 1D porous hybrid carbon materials are demonstrated. • The 1D porous hybrid carbon materials can combine the advantages of 1D carbon materials with 0D hybrid carbon materials. • 1D porous hybrid carbon materials show excellent electrochemical performance for supercapacitors. [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]

• CLACF was obtained by controlling the stabilization parameters and carbonization. • CLACF shows good electronic conductivity due to the cross-linked structures. • It exhibits a rate capability of 65.8% as the current from 0.2 to 100 A g− 1. • It delivers a energy density of 4.20 Wh kg− 1 and a power density of 1.22 kW kg−1. • It also shows perfect cyclic stability of 97.3% after 10,000 cycles at 2 A g−1. [Display omitted] Free-standing electrospun carbon nanofibers nonwovens (CNF) with an outstanding cross-linked architecture can be successfully achieved via a simple and practicable strategy by combining electrospinning, stabilization and carbonization. In this study, the hybrids of asphaltene extracted from coal residue liquefaction, polyacrylonitril and terephthalic acid are used as precursors. Due to the synergistic effect of efficient cross-linked structures and short charge transfer channels, flexible cross-linked asphaltene-based CNF (CLACF), as the binder-free supercapacitor electrode, exhibits a high capacity of 225 F g−1 at 0.2 A g−1 and an outstanding rate capability of 148 F g−1 at 100 A g−1. The developed symmetrical supercapacitor based on CLACF has a maximum energy density of 4.20 Wh kg−1 with a power density of 1.22 kW kg−1. It also has excellent cyclic stability with 97.3% capacitance retention after 10,000 cycles at 2 A g−1. [ABSTRACT FROM AUTHOR]

• Nanosheet, nanoneedle and hybrid structure of NiCo 2 O 4 nanoarrays were synthesized. • Nanoneedle-nanosheet hybrid structure improved electrochemical performance. • The hybrid structure electrode combines excellent cyclic stability and flexibility. [Display omitted] In this paper, three different morphologies of NiCo 2 O 4 nanoarrays, namely, nanosheet (S-NiCo 2 O 4), nanoneedle (N-NiCo 2 O 4) and their hybrid nanostructure (M-NiCo 2 O 4) were successfully prepared on flexible carbon cloth (CC) by a hydrothermal method. The structures, surface morphologies and compositions of the samples were respectively characterized by XRD, SEM, EDS, and XPS, and the effect of NiCo 2 O 4 morphologies on the electrochemical performances was systematically investigated. It is found that the M-NiCo 2 O 4 /CC electrode demonstrates the best supercapacitive performance among the three kinds of samples, typically its specific capacitance is 1347.4 F/g at 1 A/g (1509.1 F/cm2 at 1 mA/cm2), much higher than that of S-NiCo 2 O 4 (938.4 F/g at 1 A/g) and N-NiCo 2 O 4 (1022.4 F/g at 1 A/g). Meanwhile, the M-NiCo 2 O 4 /CC sample exhibits excellent rate capability (81.6%, from 1 A/g to 15 A/g) and cycling stability (92.4% retention after 10,000 cycles). In addition, an flexible solid-state asymmetric supercapacitor (ASC) with M-NiCo 2 O 4 /CC as positive electrode manifests great capacity retention (94% after 5000 cycles) and outstanding energy density of 41.7 Wh/kg at the power density of 750 W/kg. Moreover, the charge-discharge time shows no significant change after 2000 bends, demonstrating its application potential in the field of flexible SCs. The excellent performance is attributed to the unique hybrid porous structure of one-dimensional (1D) nanoneedles and two-dimensional (2D) nanosheets. [ABSTRACT FROM AUTHOR]

[Display omitted] • The fancy carbon nanofibers (CNFs) were prepared via coaxial electrospinning and carbonization. • The CNFs featured hollow and hierarchical porous structure. • The bridging structure formed by the carbon nanotubes (CNTs) endowed the CNFs with outstanding flexibility. • The CNFs decorated with polyaniline showed good electrochemical performance. • The assembled device could successfully power the electronics. Supercapacitors are considered to be the next generation of wearable energy storage devices because of reliable safety, high power density, and long cycle life, but the flexibility and energy density limit their practical applications. Herein, the flexible hollow hierarchical porous carbon nanofibers bridged by carbon nanotubes (HPCNFs@CNTs) are designed and constructed, followed by polyaniline (PANI) decorating to fabricate PANI@HPCNFs@CNTs. The synergistic effect of the hollow structure, hierarchical pores, in-situ nitrogen doping, and the bridging structure endows the HPCNFs@CNTs with a high specific capacitance of 461.0F g−1 (207.4 mF cm−2) while maintaining glorious flexibility under various deformation states. Besides, PANI@HPCNFs@CNTs possesses a high specific capacitance of 629.1F g−1 (405.2 mF cm−2) and remarkable cycle stability with 88.5 % capacitance retention after 5000 charging-discharging cycles. The device assembled by PANI@HPCNFs@CNTs renders an ultra-high energy density of 23.3 Wh kg−1 at a power density of 202.7 W kg−1. Furthermore, the device provides remarkable cycle stability and high-rate capability with a capacity retention of 91.3 % after 5000 cycles at 5 A g−1 and 76.7 % at 10 A g−1, respectively, demonstrating a tremendous potential to construct high-performance flexible energy storage devices. [ABSTRACT FROM AUTHOR]

• A 3D freestanding hollow porous carbon submicrofibers (HPCMFs) network was prepared by electrospinning and carbonization. • The XMoO 4 (X Ni, Co) nanosheets were uniformly grown on HPCMFs through one-step solvothermal method. • The NiMoO 4 @HPCMFs electrode exhibts high specific capacitance of 1600 F g-1 at 1 A g-1 and good cyclic stability. • Six all-solid-state symmetric supercapacitors (ASSCs) in series can power a 'DHU' Logo consisted of 36 diodes. Exploring comwposite nanomaterials with novel and stable nanostructures is of great importance for high performance supercapacitors (SCs). Herein, the nanosheet-like XMoO 4 (X Ni, Co) were uniformly grown on the carbon submicrofibers (CMFs) by a facile hydrothermal route. The NiMoO 4 @CMFs exhibits higher specific capacitance of 1485.53 F g−1 and better cycling stability with 87.6% retention after 3000 cycles at 1 A g−1 than that of CoMoO 4 @CMFs (1407.1 F g−1, 80.6% retention after 3000 cycles at 1 A g−1). To further improve the electrochemical performance of NiMoO 4 @CMFs, the hollow porous carbon submicrofibers (HPCMFs) were designed and used as a substrate for NiMoO 4. Benefiting from the hollow porous structure, the HPCMFs can provide large specific surface area for electrolyte permeating and supply more ion channels in the charge-discharge process. Therefore, the NiMoO 4 @HPCMFs exhibits a high specific capacitance of 1600.0 F g−1 at 1 A g−1 and good cycling stability of 90.7% retention after 3000 cycles. The all-solid stated symmetric supercapacitors (ASSCs) were directly assembled by using NiMoO 4 @HPCMFs as electrode without any additives, which shows good flexibility and a high energy density of 55.33 Wh kg−1 at a power density of 999.89 W kg−1. Moreover, five series ASSCs can light 'DHU' logo, indicating potential application prospect in wearable electronics. [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]

Recently, a new class of mixed polyanionic compounds with general formula Na 3 MPO 4 CO 3 (M = Ni, Mn, Fe, Co, Cu), discovered through high-throughput computations have attracted much attention for its secondary battery applications and safety aspects. Here, we combine electrochemical measurements with inductively coupled plasma-optical emission spectrometer (ICP-OES), energy-dispersive X-ray (EDX), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and an ab-initio DFT approach to unravel the dynamic self-limiting surface restructuring of Na 3 NiCO 3 PO 4 in aqueous 1 M KOH/NaOH electrolyte. The etching of lattice CO 3 2-, PO 4 3- and Na serves as the key to trigger the surface reconstruction. This work establishes a fundamental understanding of the pseudocapacitance mechanism associated with surface self-reconstruction of mixed polyanionic compounds. The reconstruction-derived self-limiting dense Ni(OH) 2 layers at the surface and its oxidation to NiOOH at anodic potentials can be attributed to the observed high-performance pseudocapacitive behavior. The surface reconstructed Na 3 NiCO 3 PO 4 electrode exhibits high specific capacitance (2378.2 F g−1 at 1 A g−1). The assembled symmetric pseudocapacitor delivers a high energy density (57.2 Wh kg−1), power density (1500 W kg−1) at 1 Ag-1 and long cycle life (13000 cycles) with 100% retention. [Display omitted] • The pseudocapacitive behavior of the Na 3 NiCO 3 PO 4 is tested. • The Na 3 NiCO 3 PO 4 undergo surface self-reconstruction. • The etching of lattice CO 3 2-, PO 4 3- and Na lead to the formation of Ni(OH) 2 at the surface. • The electrode exhibits high specific capacitance 2378.2 F g−1 at 1 A g−1 • The assembled device delivers a high energy density, power density and long cycle life. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acetylated sugarcane bagasse is blend electrospun with polyacrylonitrile successfully. • Hierarchically porous structure of carbon nanofiber is introduced without any activation. • As-prepared carbon nanofiber is flexible, porous, and with high capacitive performance. The biomass-based carbon nanofibers (CNFs) have been regarded as promising electrode materials for supercapacitors. However, the preparation of biomass-based hierarchically porous CNFs by electrospinning without any chemical and physical activation is still challenging, especially when using the whole components of lignocellulose. Herein, a feasible way to synthesize a hierarchically porous CNF by electrospinning of the blends of acetylated sugarcane bagasse (ASCB) and polyacrylonitrile (PAN) followed by carbonization is proposed. Degradation of ASCB during carbonization induced multiscale defects that led to the formation of hierarchical pores and introduced flexibility for the CNFs. The specific capacitance and areal capacitance of CNFs respectively were 289.5 F g−1 and 64.2 μF cm−2. The flexible all-solid-state symmetric supercapacitor (ASSC) derived from the CNFs showed high power density (1.26 kW kg−1) and energy density (56.0 W h kg−1), as well as high capacitance retention and great cycling stability. This synthetic strategy provides a practicable way to utilize the whole components of lignocellulosic biomass and explore its application on high-performance flexible electrode materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hybrid film is prepared by a facile and patternable vacuum-filtration method. • The hybrid film is porous, conductive, ultrathin, and flexible. • The fabricated supercapacitors can withstand an ultrahigh scan rate of 500 mV s−1. • A large areal specific capacitance of 143 mF cm−2 is achieved at 0.1 mA cm−2. Traditional porous carbon (PC)-based supercapacitors (SCs) are generally stiff and heavy owing to their rigid components and bulky additives, such as binders, conducting materials, and current collectors. Herein, a porous (574.5 m2 g−1), conductive (83.1 S cm−1), and flexible MXene (Ti 3 C 2 T x)/cellulose nanofiber (CNF)/PC hybrid film is prepared by strong interfacial interactions among its components via a facile vacuum-filtration method. Three-dimensional PC provides abundant micropores for charge storage and considerable amount of meso/macropores for fast diffusion of ions. Two-dimensional Ti 3 C 2 T x offers a significantly high conductivity of 2.6 × 103 S cm−1 and a good film-forming ability. A one-dimensional CNF ensures high mechanical properties with a tensile strength of 38.6 MPa for the hybrid film by binding the adjacent Ti 3 C 2 T x flakes and PC. Additionally, the presence of CNF and PC increases the interlayer distance between Ti 3 C 2 T x flakes, thereby providing more ion-accessible surface areas on Ti 3 C 2 T x and creating open gaps for fast ion transport. Benefiting from these electrochemically attractive properties, this film is further employed as a free-standing electrode to fabricate a high-performance quasi-solid-state SC, which demonstrates an ultrathin thickness of 0.2 mm, a high flexibility, a significantly high areal capacitance of 143 mF cm−2 at 0.1 mA cm−2, and a large areal energy density of 2.4 μWh cm−2 at 17.5 μW cm−2, with a high retention of ~50% even after increasing the power density by ~100 fold. This work will pave the way for developing free-standing MXene-based hybrid films that simultaneously possess excellent conductivity, good mechanical properties, and large charge storage capacity for flexible and high-performance SCs. [ABSTRACT FROM AUTHOR]

Coal-derived carbon nanofibers (CCNFs) have been recently found to be a promising and low-cost electrode material for high-performance supercapacitors. However, the knowledge gap still exists between holistic understanding of coal precursors derived from different solvents and resulting CCNFs' properties, prohibiting further optimization of their electrochemical performance. In this paper, assisted by laser desorption/ionization (LDI) and gas chromatography–mass spectrometry (GC–MS) technologies, a systematic study was performed to holistically characterize mass distribution and chemical composition of coal precursors derived from various ionic liquids (ILs) as extractants. Sequentially, X-ray photoelectron spectroscopy (XPS) revealed that the differences in chemical properties of various coal products significantly affected the surface oxygen concentrations and certain species distributions on the CCNFs, which, in turn, determined the electrochemical performances of CCNFs as electrode materials. We report that the CCNF that was produced by an oxygen-rich coal fragment from C6mimCl ionic liquid extraction showed the highest concentrations of quinone and ester groups on the surface. Consequentially, C6mimCl-CCNF achieved the highest specific capacitance and lowest ion diffusion resistance. Finally, a symmetric carbon/carbon supercapacitor fabricated with such CCNF as electrode delivered an energy density of 21.1 Wh/kg at the power density of 0.6 kW/kg, which is comparable to commercial active carbon supercapacitors. [ABSTRACT FROM AUTHOR]

Nitrogen-enriched carbon nanofibers carried Sn and Zn bimetallic composites with outstanding storage capacity and superior mechanical strength were facilely fabricated by electrospinning technology, amidoximation reaction modified polymer fiber, ion coordination technique introduced Zn2+ and carbonization of composite nanofibers. The introduction of amidoxime groups not only enhanced the coordination ability with Zn2+, but also increased the content of nitrogen element. In addition, due to the different thermal stability of amidoxime groups, the regulation of different types of nitrogen content can be achieved by changing the carbonization temperature, and the influence of nitrogen on the electrochemical performance was explained. At the same time, due to the role of carbothermal reduction, tin in different valence ratios was obtained and its contribution to the energy storage performance of supercapacitors was explored. Benefiting from high nitrogen-enriched level, mutation between Sn2+ and Sn4+ oxidation state and synergistic mechanism of ZnO-SnO x bimetal, the prepared composite had a high specific capacitance of 810.89 F g−1 at a current density of 0.5 A g−1, outstanding cycling stability of 119% over 5000 cycles in 4 M KOH electrolyte. What's more, we conducted a two-electrode test with the energy density of 50 Wh kg−1 at a power density of 374 W kg−1. In consequence, this novel design is believed to have great potential in high energy and power density of energy storage devices in the future. Image 1 • Nitrogen-enriched carbon nanofibers carried Sn and Zn bimetallic composites with outstanding storage capacity and superior mechanical strength were successfully prepared. • The sample showed good results due to the built-in electric field formed between different semiconductors, the introduction of hetero atom N increases the conductivity and the synergy between the bimetals. [ABSTRACT FROM AUTHOR]

We herein report the microstructure and electrochemical performance of core-shell type composites based on polyimide (PI)-derived carbon nanofiber (CNF) coated with manganese dioxide (MnO 2) for potential applications as self-standing and binder-free supercapacitor electrode materials. For the purpose, a series of core-shell type CNF/MnO 2 composites was fabricated via electrospinning of PI precursor with poly(vinyl pyrrolidone) (PVP), imidization of as-spun nanofibers, carbonization of PI/PVP nanofibers into neat CNFs, and coating of neat CNFs with MnO 2 at different dipping time of 0–60 min. The Raman, X-ray diffraction and electron microscopic analyses of the core-shell type CNF/MnO 2 composites revealed that MnO 2 nanowhiskers were coated well on the CNFs with a turbostratic graphitic structure and their coating thickness increased with the dipping time. The electrical conductivity was measured to decrease slightly from 3.6 S/cm for the neat CNF to 1.6 S/cm for CNF/MnO 2 composites with increasing the thickness of MnO 2 coating layer. As a result of synergistic effects, the core-shell type CNF/MnO 2 composite, fabricated at the dip-coating time of 10 min, exhibited a maximum electrochemical performance such as specific capacitance of ~456 F/g at 10 mV/s, energy density of ~17.8 Wh/kg, and power density of ~320 W/kg, in addition to good operational stability of ~95.8% capacitance retention after charge-discharge tests of 3000 cycles. [ABSTRACT FROM AUTHOR]