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Exploring energy storage devices and hydrogen evolution reaction electrode materials with high efficiency electrocatalytic activity, high energy density and low cost has broad prospects, but there are still huge challenges. Compared with traditional energy storage devices, supercapacitors (SCs) are a new type of energy storage device with broad development prospects. However, their practical application is significantly limited by the energy density of electrode materials. The practical application of hydrogen evolution reaction (HER) is limited by the high cost and scarcity of Pt-based precious metal catalysts. It is essential to develop materials with stable structure, low cost and abundant reserves. Here, in this paper, CoS 2 and CoSe 2 composites embedded in carbon nanofibers (CNFs) (expressed as CoS 2 -CoSe 2 /CNFs) were synthesized by electrospinning combined with in-situ growth Zeolite Imidazolate Framework-67 strategy, carbonization and subsequent selenium sulfide process. When employed as the positive material in supercapacitors, a specific capacitance of 292.2 F g−1 is achieved at a current density of 1 A g−1. The specific capacitance of asymmetric supercapacitors (ASCs) assembled with CoS 2 -CoSe 2 /CNFs-5 as positive materials remains stable with no significant change observed in specific capacitance even after undergoing 10,000 cycles. At the same time, when a current density of 10 mA cm−2 is applied in a 0.5 M H 2 SO 4 electrolyte solution, an overpotential reading of 189 mV is observed. The evidence mentioned above showcases the significant capacity of this substance for application in electrochemical energy storage and conversion. • The synergy of different components regulates the electronic structure. • The as-obtained materials exhibited a good energy storage and conversion performance. • The retention of the ZIF-67 skeleton structure can increases the number of active sites. [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]

In order to enhance the electrochemical efficiency of supercapacitors, novel active electrode materials are being developed. This study provides a unique method to synthesize an integrated structure consisting of a nickel-cobalt metal-organic framework (NiCo-MOF) on functionalized carbon nanofiber (f-CNF) utilizing a single-step solvothermal method. Physicochemical characterization confirmed the successful synthesis of the integrated system of NiCo-MOF@f-CNF. This novel structure has the potential to significantly improve the electrochemical properties of the initially prepared material for use in supercapacitors. The synthesized electrode has a higher specific capacitance/capacity value of 788 F g−1 (315.2 C g−1) at 1 A g−1 and high cycling stability. The developed hybrid device exhibited a promising specific energy of 8.6 Wh kg−1 and a high specific power of 1147 W kg−1, demonstrating potential for practical applications. The current study suggests that the proposed material can be a viable electrode for high-efficiency supercapacitors. • An integrated structure of NiCo-MOF@f-CNF nanocomposite was prepared and used as an efficient electrode in supercapacitors. • Electrical conductivity, mechanical properties, and surface accessibility were enhanced when f-CNF joined NiCo-MOF. • NiCo-MOF@f-CNF hierarchical structure exhibits a specific capacitance of 788 F g−1 at a current density of 1 A g−1. • NiCo-MOF@f-CNF//AC hybrid supercapacitor shows a specific energy of 8.6 Wh kg−1 at a specific power of 1.147 kW kg−1. [ABSTRACT FROM AUTHOR]

Iron selenide (FeSe 2), a p-type narrow band gap (1.0 eV) semiconductor, has been considered as a potential electrode material for electrochemical energy storage owing to its many benefits, including quick electron transfer, excellent electrical conductivity and exceptional theoretical specific capacity. Nevertheless, the volumetric expansion, agglomeration, low ion-diffusion capacity and other inadequacies in the process of discharging and charging. Therefore, FeSe 2 is far short of high initial coulomb efficiency, long-cycle stability, and excellent rate performance. The greatest obstacle to the practical use of energy storage systems is these drawbacks. Herein, the electrospinning and a thermally-induced selenization route are adopted to encapsulate the FeSe 2 hollow nanospheres into the intertwined Se, N co-doped carbon nanofibers (Se, N-FeSe 2 CNFs). Density functional theory calculation delivers that Se, N-FeSe 2 CNFs nanocomposite presents extremely low bandgap and high density of states at the Femi level, demonstrating significantly increased conductivity. When assembling into the all-solid-state symmetric supercapacitors (ASSSCs), the Se, N-FeSe 2 CNFs ASSSCs provide a remarkable specific capacity of 330.2 F g−1 and maintain 92.0% after 5000 cycles at 2 A g−1. Meanwhile, the resistance of charge transfer decreases from 0.73 Ω (FeSe 2) to 0.28 Ω (Se, N-FeSe 2 CNFs). Moreover, the Se, N-FeSe 2 CNFs ASSSCs deliver 128.6 Wh kg−1 (energy density) at about 800 W kg−1 (power density). Additionally, the Se, N-FeSe 2 CNFs anodes also have outstanding reversible capacity (549.5 mAh g−1 at 0.1 A g−1) and stability of long-circulation (481.3 mAh g−1 after 100 circles and 480.9 mAh g−1 after 200 circles at 0.1 A g−1) for sodium-ion batteries (SIBs). The superb property of energy storage can be due to the encapsulated structure that can maintain the integrity of structures for electrodes during electrochemical reactions and the Se, N heteroatoms doped CNFs that can conducive to ions/charges transport and storage. The designed encapsulated structure and synthesis approach have broad application prospects in electrochemical energy storage. [Display omitted] • The hollow FeSe 2 nanospheres are encapsulated in the N,Se co-doped carbon nanofibers. • The encapsulated structure can availably ameliorate the volume effect of FeSe 2 and raise the stability of electrodes. • The Se, N-FeSe 2 CNFs electrodes show outstanding electrochemical properties in supercapacitors and sodium-ion batteries. • According to density functional (DFT), the Se, N-FeSe 2 CNFs have narrow band structure and high density of states. [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]

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

For the first time, a bottom-up approach was adopted to prepare free-standing orthorhombic Nb 2 O 5 -anchored carbon nanofibers (Nb 2 O 5 @CNFs) hybrid paper via in-situ solvothermal synthesis of Nb-metal organic framework@CNFs hybrid and subsequent pyrolysis process. The nanocrystalline Nb 2 O 5 decorated on the CNF surfaces improved the charge storage performance through synergistic effect between porous CNFs (EDLC) and Nb 2 O 5 (pseudocapacitance). Moreover, the high surface area and core-shell structure of Nb 2 O 5 @CNF hybrid reduce diffusion limitations and facilitate ionic transport. The Nb 2 O 5 @CNF hybrid paper as a binder-free electrode delivered greater specific capacitance of 633.6 F/g (975.7 F/cm3) in 1 M H 2 SO 4 , compared to Li 2 SO 4 electrolyte (524.3 F/g) at 0.5 A/g. However, the Nb 2 O 5 @CNF electrode showed better cycling stability in neutral Li 2 SO 4 electrolyte than in acidic H 2 SO 4 electrolyte. The solid-state asymmetric supercapacitor (ASC) based on Nb 2 O 5 @CNF paper and activated carbon (AC) electrodes delivered higher energy density of 62.1 Wh kg−1 at 292.7 W kg−1 in Li 2 SO 4 electrolyte due to a wider working potential window (0–1.5 V), compared to H 2 SO 4 electrolyte (55 Wh kg−1). The Li 2 SO 4 -based ASC cell is also capable of producing an energy density of up to 45.6 Wh kg−1, even at a high-power density of up to 5853.6 W kg−1. The as-assembled ASC demonstrated low self-discharge rate as well as excellent bending stability, indicating its excellent prospects in real-life applications. • Flexible Nb 2 O 5 nanoparticles-anchored CNF hybrid paper fabricated form Nb-MOF@CNF for supercapacitor. • Salf-standing Nb 2 O 5 @CNF electrode achieved a high specific capacitance of 633.6 F/g (975.7 F/cm3) at 0.5 A/g. • Nb 2 O 5 @CNF//AC asymmetric device delivers a high energy density of 62.1 Wh kg−1 and excellent power of 5854 W kg-1 in 1 M Li 2 SO 4. • ASC device demonstrated excellent bending stability and low self-discharge rate. [ABSTRACT FROM AUTHOR]

The thriving energy demand of the gradually increasing population and modernised life style requires development in energy storage devices for usage in commercial electronic devices. In this particular work, we have explored electrochemical performances of bimetallic oxide Ag 2 WO 4 nanorods and tuned its performance by decorating it on the nitrogen doped carbon nanofiber (N-CNF). The Ag 2 WO 4 nanorods are synthesised by a facile route of co-precipitation method followed by ultrasonication with N-CNF. The synthesised Ag 2 WO 4 nanorods was found electrochemically active and the incorporation of N-CNF end up boosting its electrochemical performances. The obtained nanocomposites were characterised by various advanced techniques. The amount of N-CNF was determined by characterisation via the potentiostatic and galvanostatic cycle measurements and electrochemical impedance spectroscopy (EIS). The electrochemically active Ag 2 WO 4 with 20 wt% of N-CNF (Ag 2 WO 4 /N-CNF b) exhibited 2.2-fold higher charge storage capacity than pristine Ag 2 WO 4. The Ag 2 WO 4 /N-CNF b exhibited specific capacitance as high as 330 F g−1 at a constant applied current density of 1 A g−1 in 1 M KOH. The improved capacity may be due to conductive pathways provided by N-CNF. The Ag 2 WO 4 got well decorated over the N-CNF facilitating the active sites interaction with electrolyte. The symmetric device fabricated with Ag 2 WO 4 /N-CNF b electrodes exhibited excellent energy density of 10 W h kg−1 at 6000 W kg−1 at 5 A g−1. The Ag 2 WO 4 /N-CNF b electrode long-term stability has been minutely observed; the high Coulombic efficiency of 90% and high rate of capacity retention 98% even after 3000 cycles. Owing to these excellent electrochemical properties, the research work can potentially widen the opportunity to explore other profound bimetallic oxides and its nanocomposites with conductive carbon-based matrix for energy storage applications. [Display omitted] • Ag 2 WO 4 nanorods, easily synthesised by co-precipitation method is found to be electrochemically active in 1 M KOH. • Decorating Ag 2 WO 4 on N-doped CNF boost electrochemical charge storage owing to high active sites and improved conductivity. • The Ag 2 WO 4 @N-CNF nanocomposite electrode has been used further to develop electrochemical symmetric supercapacitors. • Such work open door for exploring other bimetal oxides and carbon composites and synergistic effect for various applications. [ABSTRACT FROM AUTHOR]

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

The thriving energy demand of the gradually increasing population and modernized life style requires development in energy storage devices for usage in commercial electronic devices. In this particular work, we have explored electrochemical performances of bimetallic oxide CoAl 2 O 4 and tuned its performance by decorating it on the carbon nanofibers. The CoAl 2 O 4 /CNFs are synthesized by deep eutectic solvents based hydrothermal method. The synthesized CoAl 2 O 4 nanoparticle was found electrochemically active and the incorporation of CNFs end up boosting, its electrochemical performances as battery-type electrode. The obtained nanocomposites were characterized by various techniques. The electrochemically active CoAl 2 O 4 /CNFs exhibited 2.2-fold higher charge storage capacity than CoAl 2 O 4. The CoAl 2 O 4 /CNFs exhibited specific capacity as high as 132 C/g at a constant applied current density of 1 A/g in 1 M KOH. The asymmetric device fabricated with CoAl 2 O 4 /CNFs electrodes exhibited excellent energy density of 20 Wh/kg at power density of 3000 W/kg. The CoAl 2 O 4 /CNFs electrode long-term stability has been minutely observed; the high Coulombic efficiency of 90% and high rate of capacity retention 95 %. In this work, an enzyme-free electrochemical sensor based on CoAl 2 O 4 /CNFs composite was developed for the detection of luteolin (LUT). Further modification of CoAl 2 O 4 /CNFs composite can improve the high surface area and catalytic capability of the composites. Under the optimal detection conditions, the prepared sensor has good linearity in the detection of LUT within range 30 nM − 73.5 μM with a limit of detection (LOD) of 0.0124 μM (12.4 nM). The stability and selectivity of the sensor is high, and can be used to detect LUT in various real samples. [Display omitted] • A facile, low cost hydrothermal and deep eutectic solvent method has been used to fabricate CoAl 2 O 4 spinels anchored CNFs. • CoAl 2 O 4 /CNFs interface enhanced charge transfer and higher electrocatalytic performance on Supercapacitors and electrochemical sensors. • The asymmetric device fabricated with CoAl 2 O 4 /CNFs electrodes exhibited excellent energy density of 20 Wh/kg at power density of 3000 W/kg. • The CoAl 2 O 4 /CNFs electrode long-term stability has been minutely observed; the high Coulombic efficiency of 90% and high rate of capacity retention 95 % • The CoAl 2 O 4 /CNFs/GCE platform exhibits excellent properties for LUT detection with wide linear range and low detection limit. [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 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]

Construction of hierarchically porous carbon electrode materials is considered as an efficient strategy for improving the performance of supercapacitors. Nevertheless, how to precisely control the pore structure for preferable improvement the capacitance performance and fabricate in a cost-efficient way is still a scientific challenge. In this paper, an industrial by-product of coal tar pitch is used as precursor to prepare interconnected hierarchically porous carbons, with another domestic waste of eggshell as a pore-forming template and an inner-activator, combined with KOH in-situ activation. The as-prepared porous carbons exhibit large specific surface area (S BET , 1398–2103 cm2 g−1), well-developed interconnected hierarchically architecture, and excellent electrochemical performance. Among them, the optimal TS-PCE-4 based symmetric supercapacitor possesses a high capacitance of 238 F g−1 at 0.5 A g−1 with an excellent rate capability, exhibits long cycle stability with capacitance retention of 95.85 % after 10,000 cycles, and delivers energy densities of 8.27–5.47 Wh kg−1 at power density in the range of 125–4925 W kg−1 in 6 M KOH aqueous electrolyte. This work offers a facile and low-cost route to construct interconnected hierarchically porous carbons for energy storage devices. [Display omitted] • An industrial by-product of coal tar pitch was used to fabricate the hierarchically porous carbons via a facile route. • The domestic waste of eggshell was served as a pore-forming template and an inner-activator. • The carbons show large specific surface area and well-developed interconnected hierarchically porous architecture. • The optimum sample displays outstanding supercapacitor performance. [ABSTRACT FROM AUTHOR]

The pore structure dramatically influences the electrochemical behavior of carbon nanofibers. The electrochemical performance of flexible carbon nanofibers as electrode materials for supercapacitors can be controlled by changing the size and quantity of pores. Hollow porous carbon nanofibers (HPCNFs) are prepared by coaxial electrostatic spinning and high-temperature carbonization. According to the nitrogen adsorption/desorption curve, HPCNF has a large specific surface area and good pore size distribution. In addition, cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) are used to analyze the electrochemical performance of HPCNF. Results show that the specific capacitance of hollow porous carbon nanofibers is 168.8 F/g at the current density of 1 A/g. Moreover, the specific capacitance retention of HPCNF is 95.61 % after 2000 cycles of charge and discharge at the current density of 5 A/g, exhibiting a stable cycle performance. In addition, solid-state supercapacitors assembled without any adhesives or conductive agents also show good cycle stability and excellent flexibility. As a result, HPCNF with flexibility, high specific surface area, and excellent electrochemical performance has broad prospects as an excellent electrode material for supercapacitors. Therefore, HPCNF has the advantages of good flexibility, high specific surface area, and excellent electrochemical performance. This paper proposes reasonable methods and creates more possibilities for future research and the application of flexible electrode materials for supercapacitors and flexible wearable electronic devices. [Display omitted] • Different levels of hierarchical porous carbon nanofibrous membranes are constructed. • The effect of pores in carbon nanofibers on electrochemical performance are deeply studied. • Symmetric solid-state supercapacitors exhibit excellent stability and flexibility. • The charge distribution in supercapacitor are simulated by finite element method. [ABSTRACT FROM AUTHOR]

As a promising electrode for energy storage, Fe 3 O 4 has many intriguing advantages, such as a high specific capacity, low cost, low toxicity, wide potential window and environmental benignity. However, the multi-phase changes of iron oxide during the charge and discharge process can give rise to a sharp decrease in its capacity. In addition, the low conductivity of Fe 3 O 4 may hinder the charge transfer and ion diffusion during redox process. In order to solve the above issues, this study mainly attempts to design a nanocomposite of Fe 3 O 4 encapsulated in intertwined N-doped carbon nanofibers (CNFs) via using electrospinning and high-temperature calcination. The sealed structure can efficiently relieve the volume effect of Fe 3 O 4 and raise the stability of electrodes. While a 3-dimensional interconnected conductive network composed of CNFs can increase the electroconductibility of electrodes. At the same time, the N-doping increases active sites on the surface of CNFs, providing more space for ions and charges storage. Herein, different amounts of Fe 3 O 4 are encapsulated in N-doped CNFs (Fe 3 O 4 -CNFs). Fe 3 O 4 -CNFs with 40 % content of Fe 3 O 4 (4Fe 3 O 4 -CNFs) deliver splendid electrochemical performances for all-solid-state supercapacitors and sodium-ion batteries. The specific capacitance of 4Fe 3 O 4 -CNFs supercapacitor is 184.5 F g−1 and maintains 86.2 % of initial capacity at 2 A g−1 after 5000 times. Furthermore, 4Fe 3 O 4 -CNFs as the anode for the half cell vs. Na+/Na demonstrate a splendid specific capacity of 628.1 mAh g−1 at 0.02 A g−1 and can maintain 358.1 mA h g−1 after cycling for 200 laps at 500 mA g−1. Therefore, 4Fe 3 O 4 -CNFs can be widely used in energy storage. Hollow Fe 3 O 4 nanospheres are encapsulated in the N-doped carbon nanofibers (Fe 3 O 4 CNFs) by using electrostatic spinning and high-temperature calcination method. The encapsulated structure can availably ameliorate the volume effect of Fe 3 O 4 and raise the stability of electrodes. While the addition of carbon materials can increase the conductivity of electrodes. At the same time, the N-doping increases active sites on the surface of carbon nanofibers, providing more space for ions and charges storage. The Fe 3 O 4 CNFs and the preparation method have exceptional employments in the field of energy storage. [Display omitted] • The Fe 3 O 4 carbon nanofibers with the encapsulated structure are prepared by employing electrospinning method. • The encapsulated structure can availably ameliorate the volume effect of Fe 3 O 4 and raise the stability of electrodes. • The N-doped carbon nanofibers networks can increase the conductivity and against volume expansion. [ABSTRACT FROM AUTHOR]

We introduced the concept of a novel hybrid faradaic structure as a mechanism to improve the performance of biomass-derived carbon-based supercapacitors (SCs). Organic-inorganic hybrid composition, nanostructures, porosity, surface area and active redox reactions were carefully designed. We reported the facile, cost-effective and environmentally friendly fabrication of pure lignin carbon nanofibers (LCNFs) incorporated with flower-like, multi-metal and intrinsically capacitive (Ni-Co@MnO 2) nanoparticles in a flexible and binder-free electrode for SCs by the electrospinning technique using various electrolytes (1 M Na 2 SO 4 , 0.5 M KI and 1 M Na 2 SO 4 +0.5 M KI). Mechanically robust LCNFs were used as a free-standing electrode and characterized for electrochemical performance using a two-electrode system in a Swagelok cell. Specific capacitance of the LCNFs in 1 M Na 2 SO 4 electrolyte (current density 0.1 A/g) of 129 F/g increased to 200 F/g when adding 1 % manganese oxide nanoparticles that introduced intrinsic capacitance into the nanofibers. This value further increased to 303 F/g by adding 1 % Ni-Co to the manganese oxide. The nanoflower morphology significantly increased the surface area via micro and mesopore modification on carbonization and via macropore expansion on activation. After applying a mixed electrolyte (1 M Na 2 SO 4 + 0.5 M KI), the capacitance reached 400 F/g and remained stable up to 1000 GDC cycles. Using the same composite nanofibers, 1,021 F/g was achieved using 0.5 M KI as an electrolyte. However, the latter system appeared unstable beyond 200 GDC cycles, suggesting that it can be applied as a disposable fast-charge supercapacitor. In the presence of a chemically-stable, highly-porous and partially-conductive carbon matrix, we concluded that interplay between the multi-metal oxides and electrolytes increased oxidation numbers, thereby boosting the faradaic reaction and enhancing electronic conductivity. [Display omitted] • EDLC carbon-based supercapacitor was fabricated from flower-like Ni-Co@MnO 2 nanoparticles and biomass lignin. • The unique metal oxide nanostructure led to highly-porous carbon nanofibers with unblocked micro-, meso- and macropores. • Mixed electrolyte of Na 2 SO 4 and KI led to capacitance of 400 F/g up to 1000 GDC cycles. • With KI as electrolyte, capacitance of 1,021 F/g was achieved and stable up to 200 GDC cycles. [ABSTRACT FROM AUTHOR]

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

RuO 2 nanorod-decorated tubular carbon nanofibers(CNFs) are carefully fabricated by adjusting the recrystallization temperature for use in high-performance electrochemical capacitors. The tubular structured CNFs/RuO 2 electrodes provide a short diffusion path for the ion transport through the inner hollow channel that allowed the maximum utilization of the active sites of the amorphous RuO 2 nanomaterials at the electrode/electrolyte interface. The optimized the tubular structured CNFs/RuO 2 electrodes exhibit good rate capability with a high surface capacitance, energy density, and good long-term cycling stability of 190 Fg−1, 22 Whkg−1, and 94% after 10,000 cycles, respectively, in an aqueous solution. The asymmetric cell presents a wide and stable operating voltage window, which greatly improves the energy density stored in the asymmetric device. In addition, there is no noticeable difference in the electrochemical properties under bent states, making it a flexible energy storage device for wearable applications. Hence, flexible supercapacitors using CNFs/RuO 2 electrodes with the tubular structure show low resistance, high capacitance, good rate retention, and excellent cycle stability, making it a promising material for energy storage applications. [Display omitted] • RuO 2 nanorod-decorated tubular CNFs are prepared via the recrystallization process. • CNFs/RuO 2 electrodes exhibit good rate capability with a high capacitance, energy density, and long-term cycling stability. • CNFs/RuO 2 electrode under bent states makes it a flexible energy storagCNFs/RuO2 electrodes exhibit good rate capability with a high capacitance, energy density, and long-term cycling stability.e device for wearable applications. [ABSTRACT FROM AUTHOR]

This work reports the synthesis and electrochemical properties of activated carbon nanofibers (ACNF) composited with Li 2 FeSiO 4 for supercapacitors. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller analyzer (BET), transmission electron microscopy (TEM), and thermal gravimetric analyzer (TGA). The electrochemical properties were tested using a variety of techniques, such as cyclic voltammetry (CV), galvanostatic charge-discharge (GDC), and electrochemical impedance spectroscopy (EIS). The structural transformation during charging and discharging processes was studied by in-situ time resolved X-ray absorption spectroscopy (in-situ TRXAS). The ACNF/Li 2 FeSiO 4 presented monoclinic structure with space group of P2 1 /n, although there was a small impurity of FeO. The structural transformations of iron upon cycling in the + 2 to + 3 state were responsible for high capacity of ACNF/Li 2 FeSiO 4 materials. The maximum specific capacitance of 158 Fg−1 at 2 mVs−1 and 201 Fg−1 at 0.25 Ag−1 with the corresponding specific energy of 17.8 Whkg−1 and specific power of 99.7 Wkg−1 were observed. Moreover, this composite material exhibited an excellent cycle performance through maintaining over 85% of its initial capacitance after 1000 cycles. The interesting electrochemical properties of ACNF/Li 2 FeSiO 4 composite nanostructure make it a potential candidate for supercapacitors. • ACNF/Li 2 FeSiO 4 composite nanostructure was fabricated in form of fibers by using electrospinning technique. • Carbonization temperature strongly affected to electrochemical performance. • ACNF/Li 2 FeSiO 4 exhibited maximum specific capacitance of 158 Fg−1 at 2mVs−1 and 201 Fg−1 at 0.25 Ag−1 with the corresponding specific energy of 17.8 Whkg−1 and specific power of 99.7 Wkg−1. • An excellent cycle performance through maintaining over 85% of its initial capacitance after 1000 cycles was observed. • The structural transformations of iron upon cycling in the + 2 to + 3 state were responsible for high capacity of ACNF/Li 2 FeSiO 4 materials. [ABSTRACT FROM AUTHOR]

Pyrite iron sulfide (FeS 2) is a fascinating electrode material for energy reserve devices because of its high theoretical capacity, non-polluting nature and abundant resources. However, the practical application has been extremely inhibited owing to its poor rate capacity and short cyclability caused by volume change during charge/discharge processes. In this article, a novel nanocomposite that is hollow FeS 2 nanospheres encapsulated in N/S co-doped carbon nanofibers (FeS 2 CNFs) was synthesized through electrostatic spinning. The FeS 2 CNFs nanocomposite demonstrates a terrific specific capacity of 511 F g−1 at 1 A g−1 for all-solid-state supercapacitors. The FeS 2 CNFs as electrode material for sodium-ion batteries (SIB) displays a specific capacity of 827.7 mAh g−1 and possesses a capacity of 490.6 mAh g−1 at 0.05 A g−1 after 200 cycles. The results indicate that this encapsulated structure can guarantee the integrity of electrode materials. And the abundant defects in carbon nanofibers caused by N/S co-doping may increase electrochemical reaction sites to facilitate charge transfer. The N/S co-doped FeS 2 CNFs nanocomposite exhibits a great potential for applying in SIB and supercapacitors. • Hollow FeS 2 nanospheres are encapsulated in carbon nanofibers by electrostatic spinning. • In-situ S-doping can increase the electrochemical active sites. • The incorporation of carbon nanofibers can prevent the structure collapse of FeS 2. [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]

• 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]

• The facile method for "in-situ" preparation of CNF/NiO composites is proposed. • CNF/NiO possesses 3D hierarchical porous network structure for supplying rapid, efficient channels for ion diffusion. • NiO nanoparticles uniformly anchored on CNF network supply stable capacitance. • CNF/NiO applied to supercapacitors shows high cyclic stability and a maximum energy density of 30.2 Wh kg−1. [Display omitted] The 3D porous carbon materials/transition metal oxide composite is considered to be a potential candidate for supercapacitors owing to the synergy effect of excellent pore structure, electrical conductivity and high pseudocapacitance. However, its complicated preparation and uncontrollable stability are still challenges. In this paper, we propose a facile method for "in-situ" preparing a novel kind of the NiO nanoparticles anchored on N/P-codoped carbon nanofibers network (CNF/NiO) composite. The CNF/NiO composite exhibits a 3D hierarchical porous network and high specific surface area, which supply efficient channels for the transmission of electrons/ions, and ample place for sufficient reaction between active substance and electrolyte. In addition, the NiO nanoparticles anchored on carbon nanofibers network can provide stable and excellent pseudocapacitance. When applied for supercapacitors, the CNF/NiO-based electrode can achieve the capacitance value of 674 F g−1 and 98.6% capacitance preservation after 5000 cycles in a three-electrode system. Moreover, the asymmetric supercapacitors based on CNF/NiO composite obtain a superior capacitance value of 86 F g−1 in a wide voltage of 1.6 V, and the maximum energy and power density reach 30.2 Wh kg−1 and 8.1 kW kg−1, respectively. The process has the advantages of simple operation, environmental friendliness, and possible mass production. It also provides prospects for designing and developing next-generation electrode materials for energy conversion devices. [ABSTRACT FROM AUTHOR]

• Micro-electrode arrays were fabricated on a graphite substrate using lithography and carbonization. • Conductive fibers produced via electrospinning and carbonization were decorated with RuO 2 particles. • The 3D micro-electrodes were used in fabrication of all - carbon symmetric supercapacitors. • The specific capacitance reached 219.2 F g−1 at a current density of 1 A g−1 in 1 M H 2 SO 4 electrolyte. [Display omitted] This study employed a carbon microelectromechanical system (C-MEMS) in fabricating a 3D micro-electrode array of conductive carbon cylinders directly on the surface of a graphite substrate. The capacitance of the array was further enhanced by decorating it with a composite material comprising highly-porous carbon nanofibers (CF) and electroactive RuO 2 nanoparticles to function as an active electrode. In galvanostatic charge-discharge tests, the specific capacitance of an electrode decorated with RuO 2 30 wt%/CF was 219.2 F g−1 at a current density of 0.5 A g−1, which is 2.27 times higher than that of the pristine CF electrode. When the current density was increased from 0.5 A g−1 to 3 A g−1, the capacitance retention of the RuO 2 30 wt%/CF electrode was 54.8%. A symmetric supercapacitor based on the RuO 2 30 wt%/CF composite electrode exhibited an impressive energy density of 74.2 Wh kg−1 with power density of 4333 W kg−1. It also demonstrated good capacitance retention of 80.2% following 3000 consecutive charge/discharge cycles at a current density of 2 A g−1. [ABSTRACT FROM AUTHOR]