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The preparation of composite carbon nanomaterials is one of the methods for improving the electrochemical performance of carbon-based electrode materials for supercapacitors. However, traditional preparation methods are complicated and time-consuming, and the binder also leads to an increase in impedance and a decrease in specific capacitance. Therefore, in this work, we reduced Ni-Cu nanoparticles on the surface of nitrogen-doped carbon nanofibers (CNFs) by employing an electrostatic spinning method combined with pre-oxidation and annealing treatments. At the same time, Ni-Cu nanoparticles were vulcanized to Ni–Cu–S nanoparticles without destroying the structure of the CNFs. The area-specific capacitance of the CNFs/Ni–Cu–S–300 electrode reaches 1208 mF cm−2 at a current density of 1 mA cm−2, and the electrode has a good cycling stability with a capacitance retention rate of 76.5% after 5000 cycles. As a self-supporting electrode, this electrode can avoid the problem of the poor adhesion of electrode materials and the low utilization of active materials due to the inactivity of the binder and conductive agent in conventional collector electrodes, so it has excellent potential for application. [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs) are widely used in energy storage devices due to their superior power density and long cycle lifetime. However, the limited energy densities of SCs hinder their industrial application to a great extent. In this study, we present a new combination of metallic phosphide–carbon composites, synthesized by directly carbonizing (Ni1−xCox)5TiO7 nanowires via thermal chemical vapor deposition (TCVD) technology. The new method uses one-dimensional (1D) (Ni1−xCox)TiO7 nanowires as precursors and supporters for the in situ growth of intertwined porous CNF microspheres. These 1D nanowires undergo microstructure transformation, resulting in the formation of CoNiP nanoparticles, which act as excellent interconnected catalytic nanoparticles for the growth of porous 3D CNF microspheres. Benefiting from the synergistic effect of a unique 1D/3D structure, the agglomeration of nanoparticles can effectively be prevented. The resulting CNF microspheres exhibit an interconnected conductive matrix and provide a large specific surface area with abundant ion/charge transport channels. Consequently, at a scanning rate of 10 mV s−1, its specific capacitance in 1.0 M Na2SO4 + 0.05 M Fe(CN)63−/4− aqueous solution is as high as 311.7 mF cm−2. Furthermore, the CoNiP@CNFs composite film-based symmetrical SCs show an ultrahigh energy density of 20.08 Wh kg−1 at a power density of 7.20 kW kg−1, along with outstanding cycling stability, with 87.2% capacity retention after 10,000 cycles in soluble redox electrolytes. This work provides a new strategy for designing and applying high-performance binary transition metal phosphide/carbon composites for next-generation energy storage devices. [ABSTRACT FROM AUTHOR]

Hierarchical porous activated carbon (HPAC) materials with fascinating porous features are favored for their function as active materials for supercapacitors. However, achieving high mass-loading of the HPAC electrodes remains challenging. Inspired by the concepts of carbon/carbon (C/C) composites and hydrogels, a novel hydrogel-derived HPAC (H-HPAC) encapsulated H-HPAC (H@H) composite material was successfully synthesized in this study. In comparison with the original H-HPAC, it is noticed that the specific surface area and pore parameters of the resulting H@H are observably decreased, while the proportions of nitrogen species are dramatically enhanced. The free-standing and flexible H@H electrodes with a mass-loading of 7.5 mg/cm2 are further prepared for electrochemical measurements. The experiments revealed remarkable reversible capacitance (118.6 F/g at 1 mA/cm2), rate capability (73.9 F/g at 10 mA/cm2), and cycling stability (76.6% of retention after 30,000 cycles at 5 mA) are delivered by the coin-type symmetric cells. The cycling stability is even better than that of the H-HPAC electrode. Consequently, the findings of the present study suggest that the nature of the HPAC surface is a significant factor affecting the corresponding capacitive performances. [ABSTRACT FROM AUTHOR]

• A novel supercapacitor MFC was constructed using CNFs composite cathode. • The internal resistance of CNTs/CNFs cathode was only 0.18 Ω·cm−2. • The P max of CNTs/CNFs cathode was 140% higher than that of Pt/C cathode. • MFCs with CNTs/CNFs cathode had a apparent capacitance of 0.68 ± 0.11 F·cm−2. • Both faradaic and non-faradaic processes were involved during GLV discharge. Microbial fuel cells (MFCs) as a novel, environmental-friendly wastewater treatment technology have received increasing attention. One of the major challenges for its large-scale application lies in the sluggish oxygen reduction reaction (ORR) kinetics and high catalyst costs. To address this issue, carbon nanofibers (CNFs) composite electrodes that combine both ORR catalytic activity and electrochemical capacitance behavior were fabricated in this study. Results showed that the interconnectivity of fiber aggregates and thorns-like structure of the as-prepared electrodes exhibited a high ORR catalytic activity with low internal resistance (0.18 Ω·cm−2) and high exchange current density (13.68 A·m−2). When MFCs were equipped with the carbon nanotubes (CNTs)/CNFs electrode, a maximum power density of 306 ± 14 mW·m−2 was obtained, which was 140% higher than that with Pt/C. Moreover, the CNTs/CNFs electrode showed stable catalytic activity without decline in voltage for 60 d. Both faradaic and non-faradaic processes were involved during GLV discharge. The high apparent capacitance (0.68 ± 0.11 F·cm−2) and prolonged discharge time were achieved by the CNTs/CNFs electrode, which could be attributed to the simultaneous effects of electrochemical double layer capacitance and pseudo-capacitance behavior. Together we demonstrated that the great promise of the CNTs/CNFs electrode for MFCs applications. [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]

Freestanding carbon nanotube/carbon nanofiber (CNT/CNF) composites are prepared using electrospun CNFs as skeletons in a tubular chemical vapor deposition system. The obtained CNT/CNF composites show a hierarchical structure with a high special surface area, a high conductance (1250 S cm −1 for a 10 mm × 20 mm sample), and a high flexibility. After coated with manganese dioxide (MnO 2 ) via an in-situ redox deposition for 0.5 h (∼0.33 mg), the CNT/CNF/MnO 2 electrodes show a high specific capacitance of 517 F g −1 at a scan rate of 5 mV s −1 , which is about 5.6 time higher than that CNF/MnO 2 -0.25 h ones with MnO 2 of ∼0.36 mg. Moreover, this CNT/CNF/MnO 2 electrodes show a much higher rate capability (57% at current density of 14 A g −1 ) than CNF/MnO 2 ones (24% at 14 A g −1 ), and also show a higher cycling stability (maintaining 75% of the initial capacitance at cycle number of 1000). In addition, the symmetric supercapacitor assembled using two piece CNT/CNF/MnO 2 electrodes shows their maximum energy density of 3.88 Wh kg −1 at power density of 7000 W kg −1 . The capacitance of the assembled capacitor maintains 70% after 100 bending cycles, indicating a good flexibility. These enhancements in EC performances should be due to our designed hierarchical structures. It is suggested that such freestanding flexible CNFs/CNTs/MnO 2 hierarchical composites are highly promising for high-performance flexible supercapacitors. [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]

Carbon-based supercapacitors with outstanding electrochemical performances are strongly desired for the development of portable and wearable electronics. From the free radical engineering point of view, this study innovatively developed carbon/carbon gradient-structured microspheres (CCGMs) by the strategy of "third-order graduation polymerization" and "dynamic radical oxidation". Compared to conventional hybrid materials, for the first time, the gradient structure is proved to be extremely beneficial for improving the capacitive performance. Benefiting its gradient-structured advantages, the CCGMs exhibited "three-ultrahigh" performance with gravimetric, volumetric, and areal capacitances of 408.23 F g−1, 741.11 F cm−3, and 4390 μF cm−2, respectively. In addition, the assembled all-solids-state micro-supercapacitors delivered superior volumetric and areal specific capacitances (7.704 F cm−3 and 9.245 mF cm−2 at 5 μA cm−2), excellent life-span (100% after 12000 cycles), excellent volumetric and areal energy densities (1070 mWh cm−3 and 1284 μWh cm−2). This work paves a new way to develop unique carbon composites for high‐performance energy storage devices. • A third-order graduation polymerization method was developed. • The dynamic radical oxidation method was used for ultramicroporous-confined defects. • The gradient structure could improve the "three-ultrahigh" performance of carbons. [ABSTRACT FROM AUTHOR]