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

A flexible wearable electrode consisting of nickel–cobalt sulfide (NCS) nanowires was fabricated in this study. Self-supporting NCS was grown in situ on porous carbon nanofibers without a binder as a novel material for supercapacitor electrodes. The NCS nanowires were grown using cyclic voltammetry electrodeposition, which proved to be a fast and environmentally friendly method with good controllability of the material structure. One-dimensional carbon nanofibers (C) have high surface-area-to-volume ratios, short ion transmission distances, excellent mechanical strengths, and remarkable flexibilities. Moreover, the NCS@C flexible electrode exhibited a synergetic effect with the active compounds, and the dense active sites were uniformly distributed across the entire surface of the carbon fibers, enabling rapid electron transport and enhancing the electrochemical properties of the NCS@C nanowires. The NCS@C achieved specific capacitances of 334.7 and 242.0 mAh g−1 at a current density of 2 A g−1 and high current densities (up to 40 A g−1), respectively, corresponding to a 72.3% retention rate. An NCS@C-nanofilm-based cathode and an activated-carbon-based anode were used to fabricate a flexible asymmetric supercapacitor. The device exhibited high energy and power densities of 12.91 Wh kg−1 and 358 W kg−1, respectively. [ABSTRACT FROM AUTHOR]

A flexible wearable electrode consisting of nickel–cobalt sulfide (NCS) nanowires was fabricated in this study. Self-supporting NCS was grown in situ on porous carbon nanofibers without a binder as a novel material for supercapacitor electrodes. The NCS nanowires were grown using cyclic voltammetry electrodeposition, which proved to be a fast and environmentally friendly method with good controllability of the material structure. One-dimensional carbon nanofibers (C) have high surface-area-to-volume ratios, short ion transmission distances, excellent mechanical strengths, and remarkable flexibilities. Moreover, the NCS@C flexible electrode exhibited a synergetic effect with the active compounds, and the dense active sites were uniformly distributed across the entire surface of the carbon fibers, enabling rapid electron transport and enhancing the electrochemical properties of the NCS@C nanowires. The NCS@C achieved specific capacitances of 334.7 and 242.0 mAh g−1 at a current density of 2 A g−1 and high current densities (up to 40 A g−1), respectively, corresponding to a 72.3% retention rate. An NCS@C-nanofilm-based cathode and an activated-carbon-based anode were used to fabricate a flexible asymmetric supercapacitor. The device exhibited high energy and power densities of 12.91 Wh kg−1 and 358 W kg−1, respectively. [ABSTRACT FROM AUTHOR]

Carbon nanofibers derived from lignocellulosic materials have become the most prevalent free-standing electrode material for supercapacitors due to their renewable and sustainable nature. This study used Arenga pinnata bunches (APB) as raw material for hemicellulose compounds to produce carbon electrodes through carbonization processes at 650 °C, 700 °C, 750 °C, and 800 °C, in the presence of flowing N2 gas. The variations in carbonization temperature resulted in carbon electrodes with surface morphology having a nanofiber structure with micro-meso pore distribution. According to the results, the carbonization temperature of 700 °C (APB-700) is the optimum temperature for producing electrode surface morphology with a combination of nanofiber, micro-and mesopore distributions, as well as specific surface area, specific capacitance, energy density, and power density of 1231.896 m2 g−1, 201.6 F g−1, 28.0 Wh kg−1, and 109.5 W kg−1, respectively, for the two electrode systems. This shows the combination of nanofibers and the distribution of micro-and mesopores produced with variations in carbonization temperature has the capacity to improve the performance of supercapacitor cells. Therefore, carbon nanofibers derived from Arenga pinnata bunches have the potential to be used as free-standing electrode materials for supercapacitors without employing doping, binder, electrospinning, and heteroatom template methods. [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 increasing demand for high-performance supercapacitors stimulates the rapid development of separators and electrodes. PAN-derived nanofibers via electrospinning with one-dimensional morphology, tunable nanostructure, mechanical flexibility, self-functionalities and those that can be added onto them have witnessed the intensive development and extensive applications of supercapacitors. However, the conventional PAN-derived carbon nanofibers are generally featured with rather inferior electrical conductivity and lower specific surface area. Beyond that, PAN-derived carbon nanofibers normally exhibit unsatisfactory electrochemical performance in supercapacitors. So far, several strategies have been proposed, by some of which, conspicuous success has been achieved in addressing the above key issues. Here, a comprehensive review on recent advances of the use of PAN-derived carbon nanofibers as the electrode materials for supercapacitors are provided with a focus on strategies to improve their electrochemical performances, and the basic scientific principles involved in these preparation processes. Next, the recent application progress of PAN-derived nanofibers as the electrode separators for supercapacitors is introduced. Finally, we put forward a series of critical challenges in the above research area and propose some correlative ideas for future research. [ABSTRACT FROM AUTHOR]

Nickel oxide on directly grown carbon nanofibers (CNF-NiO) electrodes were fabricated and used as cathodes for hydrogen production by water electrolysis and as electrode materials for supercapacitors. Tafel polarization from the CNF-NiO electrodes showed an improvement in the hydrogen evolution reaction. This was attributed to the increment of the electrochemically active surface area, conductivity, and the synergy effects between the nickel oxide, carbon nanofibers, and nickel foam substrate. When used for supercapacitor applications, these electrodes showed a specific capacitance of ca. 776.20 ± 26 mF cm−2 at a current density 3 mA cm−2. These electrodes prepared using a facile method also exhibited a capacitance retention of 89% even after 3000 cycles with a coulombic efficiency of 89% when cycled at 20 mA cm−2. Considering the simplistic approach of the electrode preparation, the stability, and the capacitance, this method opens an avenue to try various metal oxide deposit on the directly grown CNF template. [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]

Polystyrene foam (PF), commonly used in packaging and insulation purposes, has emerged as a recycling predicament due to its low density and is often found littering the natural environment. Herein, we have reported the utilization of discarded PF as a sacrificial material to synthesize porous carbon nanofibers (CNFs) as a sustainable technique to produce cost-effective, high-performance supercapacitor electrodes while addressing PF disposal. It was found that the solubility difference between PF and polyacrylonitrile (PAN) in N,N-dimethylformamide can be exploited to create micro-mesoporous multi-channel CNFs via electrospinning technique for enhanced ion adsorption leading to higher specific capacitance. CNF-40 (PF:PAN = 40:60) showed the best electrochemical performance with a specific capacitance of 271.6 F g−1 at a current density of 0.5 A g−1. Further, CNF-40 exhibited 100% capacitance retention after 5000 cycles, and the high energy and power densities of 18.8 Wh kg−1 and 8000 W kg−1, respectively. Moreover, in an all-solid-state supercapacitor, it demonstrated a high areal capacitance of 0.32 F cm−2, indicating great potential for application in solid-state devices. [ABSTRACT FROM AUTHOR]

High-frequency supercapacitors are being studied with the aim to replace the bulky electrolytic capacitors for current ripple filtering and other functions used in power systems. Here, 3D edge-oriented graphene (EOG) was grown encircling carbon nanofiber (CNF) framework to form a highly conductive electrode with a large surface area. Such EOG/CNF electrodes were tested in aqueous and organic electrolytes for high-frequency supercapacitor development. For the aqueous and the organic cell, the characteristic frequency at - 45° phase angle was found to be as high as 22 and 8.5 kHz, respectively. At 120 Hz, the electrode capacitance density was 0.37 and 0.16 mF cm-2 for the two cells. In particular, the 3 V high-frequency organic cell was successfully tested as filtering capacitor used in AC/DC converter, suggesting the promising potential of this technology for compact power supply design and other applications. [ABSTRACT FROM AUTHOR]

The functional composition and electrochemical behavior of the samples of N121 oxidized nanosized technical carbon in aqueous electrolytes are studied. For oxidation a 30% aqueous hydrogen peroxide (HO) solution and 2% HO with the addition of singlet oxygen or ozone were used. By means of X-ray photoelectron spectroscopy data and the analysis of the near edge X-ray absorption fine structure the features of the chemical structure of the samples are found. The oxygen concentration did not exceed 5 at.% in the samples. The analysis of cyclic voltammograms reveals that at low scan rates the specific capacitance of the material is determined by the functional composition of the surface. The sample oxidized by 30% HO solution and containing the largest number of-OH and-COOH groups demonstrated the highest capacitance in 6M KOH and in 1М HSO it was the sample with the highest concentration of C=O groups formed during the oxidation with singlet oxygen. The stability of carbon electrodes is studied in supercapacitor models. [ABSTRACT FROM AUTHOR]

Vertically aligned multi-walled carbon nanotubes (MWNTs) were grown on the surface of electroconductive silicon substrate by catalytic chemical vapor deposition (CCVD) of a mixture of toluene and ferrocene vapors at 800°С. The anisotropic structure of the array that is due to the mutual orientation of MWNTs makes such materials attractive for use as supercapacitor electrodes. The effect of iron nanoparticles encapsulated in MWNTs as a result of synthesis on the electrochemical capacity of the sample in a 1 М HSO solution was studied. Iron was removed during the thermal treatment of the MWNT array in a 20% HSO solution under the normal or hydrothermal conditions. The contribution of redox processes involving iron was shown to be comparable to the contribution of the double-layer capacity of MWNTs. The hydrothermal treatment allows easy separation of the array from the silicon substrate without any loss of electric coupling of MWNTs. [ABSTRACT FROM AUTHOR]

In this paper, the ordered mesoporous carbon nanofiber arrays (MCNAs), Nickel-Boron (Ni-B) amorphous alloys, and amorphous Ni-B/MCNAs composite for supercapacitor material have been successfully fabricated by a combination of templating method and chemical reduction process. The porous structure and large specific surface area (1270 m g) of MCNAs favor the utilization of the active material Ni-B amorphous alloys and interfacial charge transport, and provide short diffusion paths for ions. X-ray diffraction, small-angle X-ray scattering, inductively coupled plasma. Transmission electron micrographs and selected area electronic diffraction were taken to characterize the structure of the ordered MCNAs, Ni-B amorphous alloy, and amorphous Ni-B/MCNAs. Electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The results show that the amorphous Ni-B/MCNAs display superior capacitive performance (733 F g) over Ni-B amorphous alloys (562 F g) at a scan rate of 5 mV s and a good cycling stability after 1000 cycles. [ABSTRACT FROM AUTHOR]

Nitrogen-doped hierarchical porous carbon has been prepared by carbonization and hydrofluoric acid treatment of the electrospun carbon nanofibers from the polymer solutions containing thermoplastic polyurethane and also polyacrylonitrile which acted as the precursor. Controlling the nitrogen content by varying thermoplastic polyurethane mass fraction in the spinning solutions was to realize different concentration doped. Assembling a symmetrical supercapacitor by using 6 mol/L KOH as electrolyte and relevant detections were carried out. N adsorption/desorption measurement indicates the sample containing 10 wt% thermoplastic polyurethane possesses the large specific surface area of 1,126 m g and holds volume value of 0.424 cm g. The electrochemical performances were investigated by cyclic voltammetry, electrochemical impedance, and charge-discharge cycling techniques in a two-electrode system. And the sample containing 10 wt% thermoplastic polyurethane exhibits specific capacitance of 207, 203, and 198 F g at the current density of 0.2, 0.5, and 1.0 A g, respectively. Moreover, the capacity faded lower than 1 % after 8,000 cycles of charging and discharging, indicating its excellent electrochemical stability. [ABSTRACT FROM AUTHOR]

Carbon nanofibers (CNFs) and MnO@CNF nanocomposites (MCNFs) are fabricated by electrospinning and investigated as free-standing electrodes for supercapacitor. This work presents the effect of heating rate during carbonization on the electrochemical behavior of the as-prepared MCNFs electrodes in 6 mol/L KOH electrolyte. Results show that the MCNFs electrodes carbonized by relatively slower heating rate exhibit higher specific capacitance. The electronic conductivity of the slow heated MCNFs electrodes is better than that of the fast heated electrodes due to the better crystallinity of the MnO nanoparticles and the graphitic carbon layers forming on the surface of the Mn-loaded CNFs. These MCNFs electrodes demonstrate elevated rate capability and improved cycling performance without adding any polymer binder or electronic conductor. [ABSTRACT FROM AUTHOR]

Hierarchical porous carbon nanofibers serving as electrode materials are prepared through carbonization and hydrofluoric acid treatment of polyacrylonitrile-based electrospinning involving dual templates. The hierarchical porous structures are synergistically tailored by varying template contents in the spinning solution. The carbon nanofibers prepared from the electrospinning of polyacrylonitrile containing 15/15 wt.% polymethylmethacrylate/tetraethyl orthosilicate exhibit the largest specific surface area (699 m g) and microporous volume (0.196 cm g). In 6 M KOH electrolyte, a symmetrical supercapacitor equipped with the hierarchical porous carbon nanofibers demonstrates its high-end specific capacitance of 170 F g, superior rate capability, and high-power density output up to 14.7 kW kg. Cycling evolution indicates capacitance fading is only 5.8 % of initial capacitance at a current density of 1 A g even after 8,000 cycles. The excellent electrochemical performances of the carbon nanofiber are mainly ascribed to the optimized pore size distributions of both micropores and mesopores and the unique hierarchical pore structures possessed by abundant micropores. [ABSTRACT FROM AUTHOR]