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Manifold graphene-based supercapacitor (GSC) electrodes have been extensively studied recently. Numerous studies have aimed to improve the performance of GSCs by amending the surface using various treatments or by incorporating diverse materials. However, few studies have been conducted on the treatments for the back electrodes which support the active material in the GSCs. Herein, the activation of carbon nanofibers (CNFs) back electrodes was achieved through simple thermal activation using potassium hydroxide (KOH) as an activating agent to enhance the electrochemical performance of GSC electrodes. The optimized sample exhibited a specific capacitance (C sp) of 210 F/g at 100 mV/s without adversely affecting the self-discharge behavior of the electrodes. Compared to the reference electrodes formed on the nonactivated CNFs, the C sp at high rate operations of the GSC electrodes was markedly increased by 1.6 times. Morphological, elemental, and electrochemical analyses were conducted to study the effects of KOH activation on the performance enhancement of GSC electrodes. Our results present a novel research approach for enhancing GSC performance. [Display omitted] • KOH thermal activation for carbon nanofiber back electrodes was conducted. • An optimum temperature for the activation was found to be 800 °C. • The activation increased the specific capacitance for graphene supercapacitors. • The self-discharging did not worsen, indicating the practicality of this discovery. [ABSTRACT FROM AUTHOR]

The development of multifunctional composites is a challenging but necessary path for the miniaturization and integration of electronic products. Herein, versatile bimetal hydroxide (NiCo 2 (OH) 6) nanowires coated on TiO 2 modified lignin based carbon nanofibers (CNFs/TiO 2 @NiCo 2 (OH) 6) have been prepared successfully by the method of electrospinning followed by hydrothermal treatment. The loading of NiCo 2 (OH) 6 , the doping of N, and the modification of TiO 2 endow the CNFs/TiO 2 @NiCo 2 (OH) 6 with multifunctional application in energy storage and microwave absorption (MA). The abundant pores and active sites result in an excellent electrochemical performance with a high specific capacitance of 752.47 F g−1 at 1 A g−1. More importantly, the assembled supercapacitor exhibits a maximum energy density of 60.64 Wh kg−1 and a superior stability of 90.2 % even after 4000 cycles at the current density of 10 A g−1. Moreover, considering the unique porous layered-structure as well as eminent electromagnetic matching properties, as-prepared composites display an excellent MA property, which possesses a minimum reflection loss (RL min) of −46.48 dB and a maximum effective absorption bandwidth (EAB, RL < 10 dB) of 2 GHz (covering 47.62 % of X-band frequency). This work simultaneously delivers the potential application in the field of energy storage and MA. [Display omitted] • Bimetal hydroxide nanowires are grown on TiO 2 modified lignin based CNFs. • TiO 2 doping can enhance the MA properties of composites by improving the permittivity. • The doped TiO 2 generates more micro-defects and oxygen vacancies in CNFs. • The proposed design endows the versatile composites with excellent performance. • Providing a promising approach for the high-value utilization of lignin [ABSTRACT FROM AUTHOR]

The electrospun carbon nanofibers (ECNFs) with the advantages of facile preparation method, excellent electrical conductivity and ease compounding are expected to be excellent electrode materials for supercapacitors. However, the tiny specific surface area and low specific capacitance prevent the further development of carbon nanofibers. In this work, the porous coal-based carbon nanofibers (PCCNFs-2) are fabricated via a facile dual-template method, which can be directly employed as a flexible electrode material for supercapacitors without the addition of any conductive agents and binders. As a result, the flexible self-supporting electrode (PCCNFs-2) achieves a specific capacitance of 262.0 F g−1 at a current density of 1 A g−1, excellent rate performance (81.0 % capacitance retention at a current density of 20 A g−1) and excellent cycling stability (after 10,000 cycles, 124 % capacity retention at 2 A g−1). Furthermore, the aqueous symmetrical supercapacitors (SCs) assembled with melamine foam as the storage electrolyte at an operating voltage of 1.2 V achieved an energy density of 18.5 Wh kg−1 at a power density of 150.5 W kg−1. The effective construction of this porous carbon nanofiber assures the structural integrity and achieves excellent electrochemical performance of the electrode material, which develops a new strategy for efficient utilization of porous coal-based carbon nanofibers in supercapacitors. [Display omitted] • Flexible self-supporting PCCNFs-2 electrodes were prepared via dual-template strategy. • PCCNFs-2 electrode has a capacity retention rate of 124 % after 10,000 cycles. • The symmetrical supercapacitors with PCCNFs-2 exhibits high energy density and long cycling lifespan. [ABSTRACT FROM AUTHOR]

Preasphaltene (PA) in coal liquefaction residues is a major precursor for synthesizing carbon nanofibers film by electrospinning, stabilization and carbonization. In this study, terephthalic acid (TPA) was used as an additive in a spinning solution to improve the nanostructural and electrochemical performance of PA based carbon nanofibers (PACF). The effect of TPA on the stabilization, carbon nanostructural characteristics and electrochemical performance of the supercapacitors for PACF were characterized and evaluated. The results showed that TPA could promote the oxidation of PA and decelerate the weight loss rate of the stabilized fibers, affording a good fiber morphology and satisfactory flexibility. Furthermore, the introduction of TPA facilitated the generation of pore structures in carbon nanofibers, which heightened the specific surface area, resulting in an elevated specific capacity (204 F g−1 at 1 A g−1) alongside excellent cycling stability (97.5 % capacitance retention after 10,000 cycles at 2 A g−1). [Display omitted] • The effect of TPA on the stabilization of PA/PAN film was investigated. • The influence of TPA in nanostructural characteristics of PACF was evaluated. • TPA improved the pore structures and enhanced specific surface area of PACF. • TPACF-3 exhibits good electrochemical performance for SCs. [ABSTRACT FROM AUTHOR]

In this study, amorphous zinc oxide incorporated with sulfur-doped carbon composite nanofiber (ZnO@S-CNF) was obtained through a facile electrospinning technique and calcination. The ZnO@S-CNF composite was characterized in detail in order to understand the structural features of the electrodes and applied for supercapacitors. As a self-supporting electrode, it achieved a high capacitance of 209 F/g at 1 A/g and sustained 158 F/g at 10 A/g. Also, an asymmetric supercapacitor (ASC) assembled by ZnO@S-CNF as the positive and carbon nanofiber as the negative electrode (−CNF//ZnO@S-CNF+) achieved a specific energy of 11.2 Wh/kg at a specific power of 900 W/kg in 0–1.8 V. The excellent electrochemical performance can be ascribed to the enhanced surface area, increased micropore volume, and heteroatom content. This study can provide a feasible way for the development of other carbon composite electrodes with remarkable performance. [Display omitted] • Modification of the electronic structure by heteroatom doping, thereby promoting the supercapacitive performance. • Increased surface area with the synergistic effect of amorphous zinc oxide and introduction of sulfur in the carbon skeleton. • ASC device with a specific energy of 11.2 Wh/kg at a specific power of 900 W/kg. [ABSTRACT FROM AUTHOR]

In this work, terephthalic acid (TPA) is chosen as a plasticizer and pore-forming additive to promote the stabilization and improve the electrochemical performance of polyacrylonitrile based carbon nanofibers film (PANCF). The plasticizing mechanism of TPA is systematically investigated. Meanwhile, the effect of TPA on the nanostructural characteristic and electrochemical performance is also studied. The introduction of TPA could promote the oxidation, cyclization and dehydrogenation reaction among PAN molecules by the forming of anhydride compounds during the stabilization. TPA modified PANCF (T-PANCF) exhibits better flexibility, smaller diameter, higher weight residual, more defective sites, suitable heteroatom content and larger specific surface area and pore volume compared to those of PANCF. When used as the electrode material for supercapacitors, T-PANCF shows a high specific capacitance of 182 F g−1 at 1 A g−1 and 81 % capacitance retention of it at 100 A g−1. This method is very fascinating for preparing high performance PANCF due to its simple operation and short production time. [Display omitted] • The effect of TPA on the stabilization of PAN film was investigated. • The influence of TPA in nanostructural characteristics of PANCF was evaluated. • TPA promoted the formation of pore structures and enhanced S BET of PANCF. • T-PANCF exhibited good electrochemical performance for SCs. [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]

Interest in the direct growth of carbon nanostructures on metal substrates is growing, especially in the field of supercapacitors, fuel cells, batteries and sensors. This paper presents results on the growth of carbon nanofibers (CNF) without the requirement of an external catalyst directly on nickel foam (Ni-foam) at a relatively low temperature of 400 °C. Etching of Ni-foam leads to the growth of CNF forests covering entirely the internal surfaces of the Ni-foam, with CNF diameters that can be tuned between 78 ± 32 nm and 375 ± 35 nm through a change in the growth temperature between 400 and 700 °C. Etching was found to be important to obtain a uniform surface CNF coverage and growth, particularly at higher temperatures. These CNF/Ni-foam composites yield 3D nano-scale internal forest structures in good contact with the micro-scale porosity of the metallic foam electrode. This work provides a foundation to use binderless CNF composite electrodes to obtain higher capacitance. [ABSTRACT FROM AUTHOR]

Free-standing carbon nanofibrous membranes are prepared by carbonization and H 2 O 2 activation of electrospun polyimide nanofibrous membranes. The green and facile H 2 O 2 activation method not only regulates the pore structure of carbon nanofibers but also introduces rich oxygen species, rendering a hierarchically porous and heteroatom-doped carbon electrode for supercapacitors. The optimal electrode (PI800-8) shows a high specific capacitance of 339.9 F g−1 (0.5 A g−1, 6 M KOH electrolyte) and excellent cycle durability with a capacitance retention of 98.4 % after 50,000 cycles (5 A g−1). Particularly, a non-aqueous symmetric supercapacitor assembled with 1 M Et 4 NBF 4 electrolyte shows a high operating voltage of 2.8 V, and delivers the maximum energy/power density of 37.3 Wh kg−1 and 28.0 kW kg−1, respectively. The H 2 O 2 activation method provides a green, efficient, and versatile strategy to improve the pore properties and chemical compositions of porous carbon materials towards energy applications. [Display omitted] • The N/O-codoped carbon nanofibrous membranes were prepared by commercial electrospun polyimide nanofibrous membranes. • The green H 2 O 2 activation was proposed to ameliorate the pore and chemical properties of carbon nanofibrous membranes. • Excellent comprehensive performance was presented for both aqueous/non-aqueous symmetric supercapacitor. [ABSTRACT FROM AUTHOR]