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The Lotus-leaf-stem-like NiCo 2 S 4 /CNF composite is prepared with mono-disperse NiCo 2 S 4 nanocrystals in-situ electrospun within porous CNFs for improved supercapacitive performance. [Display omitted] • DFT calculation results show that NiCo 2 S 4 has higher electronic conductivity and lower adsorption energy of OH– than NiS and CoS. • One-step electrospinning of metal ions and carbon sources by a very simple method. • Ex-situ XPS characterization test verifies that NiCo 2 S 4 /CNF has higher proportion of metal ions involved in electrochemical reactions and larger number of transferred electrons. • l -ASC and S-ASC devices have high-performance energy storage. S-ASC devices have excellent low-temperature performance and stability. Bimetallic sulfide NiCo 2 S 4 has been regarded as a potential supercapacitor electrode material with excellent electrochemical performance. However, the origin of its high specific capacity is little studied, and the design of a rational structure still remains a challenge to exert its intrinsic advantage. In this work, the advantage of NiCo 2 S 4 over NiS and CoS is explained by density functional theory calculation from the aspects of energy band, density of electronic states and OH– adsorption energy. It is proved that the synergistic effect of Ni and Co in NiCo 2 S 4 can reduce its OH– adsorption energy and provide more active electrons near the Fermi level, thus promoting electrochemical reaction kinetics in supercapacitors. Then, a simple electrospinning method is used to in-situ load mono-disperse NiCo 2 S 4 nanocrystals within amorphous carbon nanofibers, obtaining a porous, lotus-leaf-stem-like one-dimensional nanocomposite of NiCo 2 S 4 /CNF. Ex-situ XPS characterization confirms that the proportion of metal ions involved in electrochemical reactions and the number of transferred electrons in NiCo 2 S 4 /CNF during the redox reaction are significantly higher than those in mono-metallic sulfides (NiS/CNF and CoS/CNF), verifying the calculation results. With its boosting reaction kinetics, the NiCo 2 S 4 /CNF gives the specific capacity of 757.97C g−1 at 1 A/g and the capacity retention of 95.15 % after 10,000 cycles at 5 A/g, both greater than NiS/CNF and CoS/CNF. The NiCo 2 S 4 /CNF, as the positive electrode, and activated carbon, as the negative electrode, are assembled into liquid-state and solid-state asymmetric supercapacitor (ASC) devices, and both show high power density (760.6 W kg−1 for liquid-state device and 1067.4 W kg−1 for solid-state device), high energy density (52.25 Wh kg−1 for liquid-state device and 48.54 Wh kg−1 for solid-state device) and great cycle stability. Moreover, the solid-state ASC device possesses excellent low temperature capacity and reversibility, further demonstrating the wide application potential of the NiCo 2 S 4 /CNF composite. [ABSTRACT FROM AUTHOR]

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

[Display omitted] • A simple hydrothermal synthesis reaction was used to prepare the ternary composite electrode material with multicore-shell. • A large number of flower-like nanospherical δ-MnO 2 were grown on the outermost layer. • Using the control variable method and the Box-Behnken experimental design model in RSM. • The effects of reaction parameters on the growth of MnO 2 were discussed in detail. In this study, a multicore-shell ternary composite electrode material (MnO 2 @Ppy@NPCNFs) with excellent electrochemical performances was prepared by using surface modification, in which core–shell Ppy@N-doped porous carbon nanofibers (Ppy@NPCNFs) with large specific surface area and high conductivity were used as the substrate (a multicore layer), and MnO 2 was loaded on the substrate by hydrothermal synthesis to form a shell layer, further improving the SC of electrode material. The parameters of hydrothermal growth of MnO 2 on Ppy@NPCNFs were explored by means of the control variable method and response surface methodology, and the optimal parameters were predicted and verified. Electrochemical test results showed that the SC of MnO 2 @Ppy@NPCNFs prepared under the optimal reaction parameters was as high as 595.77 F g−1, and its capacitance retention was 96.2 % after 1000 cycles. Moreover, a symmetric supercapacitor prepared with the optimal multicore-shell electrode showed an energy density of 9.36 Wh kg−1 at a power density of 1000 W kg−1 and a retention rate of 92.46 % after 1000 cycles, indicating the promising application of multicore-shell ternary composite electrode material in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

A series of core-triple-shelled GCNF/PANI/NCO nanostructures have been fabricated via a facile strategy. Taking full advantage of the free-standing architecture of graphene-coated electrospun carbon nanofibers (GCNF), high conductivity and flexibility of the polyaniline (PANI) layers, and abundant active sites of nickel carbonate hydroxide (Ni 2 (CO 3)(OH) 2) nanosheets, the optimal electrode exhibits a high specific capacitance of 1565F g−1 at 1 A/g, which exceeds almost all of the reported nickel carbonate hydroxide-based electrodes in literatures. A hybrid supercapacitor delivers a high energy density of 35.4 Wh kg−1@750 W kg−1 and a long cycle lifespan. This strategy enables the controllable synthesis of core-triple-shelled hierarchical materials applicable to diverse electrochemical applications. [Display omitted] • We prepared the core-triple-shelled GCNF/PANI/NCO fiber-based films via a new route. • The optimal electrode exhibits high electrochemical properties via joint actions. • A hybrid supercapacitor displays large specific capacities and high energy density. • This strategy provides a new way to synthesize other core-triple-shelled materials. Designing novel efficient electrode materials with controlled hierarchical structure and composition for advanced supercapacitors remains a great challenge. Herein, a core-triple-shelled hierarchical GCNF/PANI/NCO nanostructure has been designed and fabricated by sequential growth of the conductive polyaniline (PANI) layers and nickel carbonate hydroxide (Ni 2 (CO 3)(OH) 2) nanosheets on the graphene-coated electrospun carbon nanofibers (GCNF) via a facile wet-chemical strategy. Taking full advantage of the free-standing architecture of graphene-coated electrospun carbon nanofibers, high conductivity and flexibility of the PANI layers, and abundant active sites of Ni 2 (CO 3)(OH) 2 nanosheets, the optimal GCNF/PANI/NCO (2 h) electrode exhibits a high specific capacitance of 1565F g−1 at 1 A/g and enhanced rate capability, which are higher than those of the GCNF, GCNF/PANI, and GCNF/NCO (2 h) electrodes at the same situation, and also exceeds most of the reported nickel carbonate hydroxide-based electrodes in literature. The superior performance should be mainly ascribed to the collaborative contribution of each component. Moreover, a self-assembled GCNF/PANI/NCO//AC hybrid supercapacitor delivers a high energy density of 35.4 Wh kg−1@750 W kg−1 and a long cycle lifespan. This strategy enables the controllable synthesis of core-triple-shelled hierarchical materials applicable to advanced electrochemical applications. [ABSTRACT FROM AUTHOR]

PPy@B-NCS/CNF composites exhibit excellent electrochemical performance as electrode materials for asymmetric supercapacitors. [Display omitted] • Thedensity functional theory calculation shows that the doping of boron increases the conductivity and oxidation resistance of Ni-Co sulfide, reduces the adsorption energy of hydroxide ions, and thus significantly improves the electrochemical performance. • Electrospinning Carbon Nanofibers (CNF) as the framework and substrate of composites can effectively improve the specific surface area and conductivity of electrode materials, showing excellent electrochemical properties. Surface coating of polypyrrole further improves conductivity and electrochemical stability. • The PPy@B-NCS/CNF delivers high specific capacity, high rate performance and excellent cycle stability. The device has good cycle reversibility and stability after low temperature treatment back to 20 °C. Although nickel–cobalt bimetallic sulfides have been widely studied for supercapacitor electrodes, how to obtain high specific capacity and cycle stability is still an important challenge. Here, an efficient chemical redox method is used to adjust the crystal and electronic structure of cobalt–nickel sulfide (NCS) via B doping, combined with electrospinning technology and conductive polymer polypyrrole (PPy) coating to facilitate faraday redox reactions and obtain high energy density electrode materials. The resulting composite with boron-doped nickel–cobalt sulfide on electrospinned carbon nanofibers with polypyrrole-coating (PPy@B-NCS/CNF) has a high specific capacity (751.61C/g at 1 A/g) and good cycle stability (82.49 % retention after 4000 cycles at 5 A/g). With PPy@B-NCS/CNF as the positive electrode and activated carbon as the negative electrode, an asymmetric supercapacitor (ASC) is prepared. It has excellent electrochemical properties with a power density of 65.58 Wh kg−1 and an energy density of 819.72 W kg−1. The low-temperature performance test shows high reversibility, which provides the possibility for the development of low-temperature electrolytes. Finally, density functional theory (DFT) explains that B-doped NCS has better electrochemical properties from the energy band and state density. [ABSTRACT FROM AUTHOR]

PPy@B-NCS/CNF composites exhibit excellent electrochemical performance as electrode materials for asymmetric supercapacitors. [Display omitted] • Thedensity functional theory calculation shows that the doping of boron increases the conductivity and oxidation resistance of Ni-Co sulfide, reduces the adsorption energy of hydroxide ions, and thus significantly improves the electrochemical performance. • Electrospinning Carbon Nanofibers (CNF) as the framework and substrate of composites can effectively improve the specific surface area and conductivity of electrode materials, showing excellent electrochemical properties. Surface coating of polypyrrole further improves conductivity and electrochemical stability. • The PPy@B-NCS/CNF delivers high specific capacity, high rate performance and excellent cycle stability. The device has good cycle reversibility and stability after low temperature treatment back to 20 °C. Although nickel–cobalt bimetallic sulfides have been widely studied for supercapacitor electrodes, how to obtain high specific capacity and cycle stability is still an important challenge. Here, an efficient chemical redox method is used to adjust the crystal and electronic structure of cobalt–nickel sulfide (NCS) via B doping, combined with electrospinning technology and conductive polymer polypyrrole (PPy) coating to facilitate faraday redox reactions and obtain high energy density electrode materials. The resulting composite with boron-doped nickel–cobalt sulfide on electrospinned carbon nanofibers with polypyrrole-coating (PPy@B-NCS/CNF) has a high specific capacity (751.61C/g at 1 A/g) and good cycle stability (82.49 % retention after 4000 cycles at 5 A/g). With PPy@B-NCS/CNF as the positive electrode and activated carbon as the negative electrode, an asymmetric supercapacitor (ASC) is prepared. It has excellent electrochemical properties with a power density of 65.58 Wh kg−1 and an energy density of 819.72 W kg−1. The low-temperature performance test shows high reversibility, which provides the possibility for the development of low-temperature electrolytes. Finally, density functional theory (DFT) explains that B-doped NCS has better electrochemical properties from the energy band and state density. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two composite methods of carbon nanofibers and metal compounds are proposed. • Iron carbides are evenly distributed among the carbon nanofibers, resulting in improved electrical and electrochemical properties. • Hierarchical 3D hollow structure of CNF@NiCoS-650 relieve volume expansion and facilitate quick ion diffusion. • The Fe 3 C@CNF-650//CNF@NiCoS-650 hybrid supercapacitor exhibits high energy density. To meet the crucial demand for high-performance supercapacitors, much effort has been devoted to exploring electrode materials with nanostructures and electroactive chemical compositions. Herein, iron carbide nanoparticles are encapsulated into carbon nanofibers (Fe 3 C@CNF-650) through electrospinning and annealing methods. Nickel-cobalt sulfide nanoparticles are hydrothermally grown on electrospun carbon nanofibers (CNF@NiCoS-650). The Faradaic electrochemical reactions of transition metal compounds improve the specific capacitance of the developed electrode. Meanwhile, the electrically conductive framework of carbon nanofibers facilitates Faradic charge transport. In detail, the Fe 3 C@CNF-650 anode and CNF@NiCoS-650 cathode achieve specific capacitances of 1551 and 205 F g−1, respectively, at a current density of 1 A g−1. A hybrid supercapacitor that is fabricated from the Fe 3 C@CNF-650 anode and CNF@NiCoS-650 cathode delivers an energy density of 43.2 Wh kg−1 at a power density of 800 W kg−1. The designed nanostructures are promising for practical supercapacitor applications. [ABSTRACT FROM AUTHOR]

N/P dual-doped three-dimensional porous carbon was synthesized via nano-CaCO 3 template-assistant carbonization of intumescent flame retardants (IFRs) precursor. [Display omitted] Heteroatom-doped three-dimensional (3D) porous carbons possess great potential as promising electrodes for high-performance supercapacitors. Inspired by the inherent features of intumescent flame retardants (IFRs) with universal availability, rich heteroatoms and easy thermal-carbonization to form porous carbons, herein we proposed a self-assembling and template self-activation strategy to produce N/P dual-doped 3D porous carbons by nano-CaCO 3 template-assistant carbonization of IFRs. The IFRs-derived carbon exhibited large specific surface area, well-balanced hierarchical porosity, high N/P contents and interconnected 3D skeleton. Benefitting from these predominant characteristics on structure and composition, the assembled supercapacitive electrodes exhibited outstanding electrochemical performances. In three-electrode 6 M KOH system, it delivered high specific capacitances of 407 F g−1 at 0.5 A g−1, and good rate capability of 61.2% capacitance retention at 20 A g−1. In two-electrode organic EMIMBF 4 /PC system, its displayed high energy density of 62.8 Wh kg−1 at a power density of 748.4 W kg−1, meanwhile it had excellent cycling stability with 84.7% capacitance retention after 10,000 cycles. To our best knowledge, it is the first example to synthesize porous carbon from IFRs precursor. Thus, the current work paved a novel and low-cost way for the production of high-valued carbon material, and expanded its application for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

As ultralight and superelastic aerogels are quite desirable for pressure sensing and energy storage applications, superelastic and ultralight carbon nanofiber (CNF)/transition metal carbides and carbonitrides (MXenes) hybrid aerogels with anisotropic microchannels are thus fabricated by liquid nitrogen-assisted unidirectional-freezing followed by freeze-drying. The CNFs with high aspect ratios entangle and assemble into the interconnected scaffolds, while the MXene sheets enhance structural stability of the framework of CNFs and endow the aerogels with satisfactory electronic conductivities. Benefiting from the stable architecture with orientated microchannels, the CNF/MXene aerogel (CNF/MX) with an ultralow density of 4.87 mg cm−3 exhibits superb compressible resilience at the strain of 50% for at least 5000 cycles and a high strain of 95% for 500 cycles. Importantly, the outstanding strain- or pressure-responses endow the CNF/MX aerogel sensor with high sensitivity (65 kPa−1), ultralow detection limit (<5 Pa), rapid response (26 ms), large workable strain range (0–95%), and superb response stability. Furthermore, the presence of MXene with excellent electrochemical activity makes the binder-free CNF/MX electrode exhibit a high rate performance with 80% capacitance retention when the current density increases by 100 times and a high cycling stability with capacitance retention of 90% after 20,000 cycles at 5 A g−1. [ABSTRACT FROM AUTHOR]

Reducing the material size could be an effective approach to enhance the electrochemical performance of porous carbons for supercapacitors. In this work, ultra-fine porous carbon nanofibers are prepared by electrospinning using lignin/ polyvinylpyrrolidone as carbon precursor and zinc nitrate hexahydrate (ZNH) as an additive, followed by pre-oxidation, carbonization, and pickling processes. Assisted by the ZnO template, the pyrolytic product of ZNH, abundant micropores are yielded, leading to the formation of microporous carbon nanofibers with specific surface area (SSA) up to 1363 m2 g−1. The average diameter of the lignin-based ultra-fine porous carbon nanofibers (LUPCFs) is effectively controlled from 209 to 83 nm through adjusting the ZNH content. With good flexibility and self-standing nature, the LUPCFs could be directly cut into electrodes for use in supercapacitors. High accessible surface, enriched surface N/O groups, and reduced fiber diameters endow the LUPCFs-based electrodes with an excellent specific capacitance of 289 F g−1. The reduction of fiber diameters remarkably improves the rate performance of the LUPCFs and leads to a low relaxation time constant of 0.37 s. The high specific capacitance of 162 F g−1 is maintained when the current density is increased from 0.1 to 20 A g−1. Besides, the fabricated LUPCFs show exceptional cycling stability in symmetrical supercapacitors, manifesting a promising application prospect in the next generation of supercapacitors. [ABSTRACT FROM AUTHOR]

Hierarchical MnO 2 -based fiber-in-tube and particle-in-tube nanostructures with unique chemical compositions and gradient pores have been rationally designed and constructed using a simple self-template method for high-performance asymmetric supercapacitors, which deliver extraordinarily excellent energy density. • MnO 2 -based fiber-in-tube and particle-in-tube nanostructures are designed. • The hierarchical architectures are fabricated via a simple self-template approach. • The novel nanotubes yield superior specific capacity as supercapacitor electrodes. • The asymmetric supercapacitors deliver extraordinarily excellent energy density. Manganese dioxide (MnO 2) promises for high-performance asymmetric suprecapacitors, owing to its high theoretical capacity, abundant source, and low cost. However, insufficient practically-achievable capacity and relatively narrow voltage window in alkaline electrolyte are blocking high energy density of MnO 2 -based supercapacitors, where strategies for activating its capacitive performance and widening voltage window are the top priorities to solve the bottleneck problems. Herein, both the fiber-in-tube (NCCM-FiT) and particle-in-tube (NCCM-PiT) nanostructures coulping active NiCoO x nanoparticles and conductive carbon with MnO 2 tubes have been purposely fabricated, using the electrospun nickel cobalt oxides/carbon nanofibers (NCO/CNFs) as the self-template agents for enhanced energy density of MnO 2 -based supercapacitors. These hierarchical hollow nanotubes with gradient pores and unique compositions yield excellent capacitive properties, in terms of a competitive capacity (431.7 F g−1 or 431.7 C g−1, 0.5 A g−1), which is 2.7 times that of the MnO 2 nanotubes-based electrodes. A maximum energy density of 46.4 Wh kg−1 is obtained at the power density of 400 W kg−1 for the asymmetric device assembled with the NCCM-PiT-based positive electrode and the electrospun CNFs-based negative electrode. The remarkable energy density demonstrated by these hierarchical hollow nanotubes exemplifies a novel and effective design in electrode materials for the asymmetric supercapacitors (ASCs) with superior performance. [ABSTRACT FROM AUTHOR]

Controllable synthesis of carbon nanofibers (CNFs) with hierarchical porosity and high flexibility are extremely desirable for CO 2 adsorption and energy storage applications. Herein, we report a nickel cobaltite/carbon nanotubes doped CNFs (NiCo 2 O 4 /CNTs CNFs) mesoporous membrane that shows well-developed flexibility, tailored pore structure, hydrophobic character, and high stability. Ascribed to these unique features, NiCo 2 O 4 /CNTs CNFs membrane shows high CO 2 capture of 1.54 mmol/g at 25 °C and 1.0 bar, and electrochemical measurements for supercapacitors exhibit good performance with specific capacitances of 220 F/g (in 1 M KOH) at a current density of 1 A/g. The successful synthesis of such hybrid membrane provides new insight into development of various multifunctional applications. [ABSTRACT FROM AUTHOR]