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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]

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]

In this study, an electrospinning method was used to produce highly conductive freestanding carbon nanofibers (CNFs). The freestanding CNFs are compatible with hierarchical growth techniques, such as hydrothermal processes, for the nanostructure engineering of supercapacitor electrodes with enhanced electrochemically active sites. Therefore, the flower-like FeMoO 4 @CNF nanosheets were investigated to improve the electrochemical performance using aqueous and neutral electrolytes (Na 2 SO 4 and K 2 SO 4). The optimized FeMoO 4 @CNF electrode exhibits areal capacitances of 252 and 220 mF·cm−2 at a high current density of 2.5 mA·cm−2 with Na 2 SO 4 and K 2 SO 4 electrolytes, respectively. The wide potential window (1.6 V) of the symmetric supercapacitor delivered maximum energy densities of 22.4 and 19.6 μWh·cm−2 at a power density of 2 mW·cm−2 for Na 2 SO 4 and K 2 SO 4 electrolytes, respectively. [ABSTRACT FROM AUTHOR]

Transition metal sulfides (TMSs) are favorable as electrode materials for supercapacitors (SCs) because of their high theoretical capacity, low cost, fascinating redox reversibility, electronic conductivity, and reduced charge transfer resistance. However, TMS electrodes suffer from weak compatibility and combination at heterogeneous interfaces, resulting in TMS stripping and electrode capacity degradation during long-term charging/discharging processes. Herein, we used a convenient, feasible, cheap, and environmentally friendly hydrothermal method to grow S/CoS2/NiS2in situ on Pien Tze Huang-based porous carbon (PZH) to promote the poor electric conductivity and unsatisfactory cycling stability of TMSs. Furthermore, TMSs can be tightly embedded on the surface of PZH to prevent falling off or collapse during long-term processes and usage. The prepared S/CoS2/NiS2/PZH electrode possessed an excellent specific capacitance of 1159.2 F g−1 at 0.5 A g−1, and after 10 000 cycles at 5 A g−1, the capacitance retention was maintained over 84.6%. This in situ method is promising for the development of stable TMS-based electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]

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]

Waste orychophragmus violaceus was used to prepare a novel 3D self‐doped (N/O) porous carbon (OPC). The aim was to expand the application and increase the value of waste orychophragmus violaceus. In order to improve its specific capacitance, composites OPC@MnO2x of OPC and MnO2 were prepared by simple hydrothermal method. In 6 M KOH, specific capacitance obtained by OPC at 1 A g−1 is 268 F g−1, surprisingly, specific capacitance of OPC@MnO232 can be up to 419 F g−1 at 1 A g−1 and its capacitance retention rate is as high as 83.62 % after 10000 cycles (20 A g−1). The energy density of OPC@MnO232//OPC asymmetric supercapacitor in 1 M Na2SO4 can even reach 14.22 Wh kg−1 at 400 W kg−1, besides, it showed good cycling stability after 10000 cycles (20 A g−1), with capacitance retention rate of up to 86.64 %. Finally, the device is tested in an application. Connecting two identical asymmetric supercapacitors in series enables red LED to emit greater than 90 s. Overall, this study confirms that the waste orychophragmus violaceus derived porous carbon can reduce the wastage of waste resource, additionally, the composite material prepared is an electrode material for high‐performance supercapacitors with broad prospects. [ABSTRACT FROM AUTHOR]

To overcome the drawback of carbon nanofibers (CNFs) such as the low energy density and low specific capacitance as electrode for supercapacitors, SiO 2 /PANI@CNFs composite was prepared by layer-by-layer (LbL) assembly technique, in which the SiO 2 served as a component for improving capacitive behavior. Polyaniline (PANI) is used as nucleation site for synthesizing SiO 2 particles as well as active material for improving capacitance. In this study, SiO 2 particles were synthesized using biosilicification process as a bioinspired, rapid, and facile synthetic route for SiO 2 particles at ambient temperature and pressure, etc. To elucidate effect of SiO 2 on the electrochemical properties, SiO 2 /PANI@CNFs samples were prepared by varying concentration ratio of tetraethyl orthosilicate (TEOS) to CNFs. It was observed that the specific surface area and the capacitance are highly dependent on the TEOS concentration. The capacitance of the composite prepared at the TEOS concentration of 0.19 mmol reaches 412 F g−1 at the current density of 1 A g−1. These results are attributed to increased specific surface area from interstitial voids between SiO 2 particles and hydrophilic nature of SiO 2 particles, which offers sufficient channels for rapid ion diffusion and leads easy accessibility to the active sites for the electrochemical reaction between electrode and aqueous electrolyte. Due to its excellent electrochemical and biocompatible properties, bioinspired SiO 2 inorganic material will promote the development of energy storage devices in biomedical and environmental electronics. [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]

Carbon materials play an important role in supercapacitors due to their structural diversity, rich surface morphology, excellent chemical stability and highly active surfaces. Currently, there are many reports on the synthesis methods for carbon-based materials. The molten salt method stands out among the many methods for its advantages of economy, environmental protection, high efficiency, and maneuverability. Here, we focus on the different roles played by molten salts as templates, sealants, reaction media, and catalysts from the point of view of their functions. The properties and selection principles of the molten salts are discussed in depth, focusing on the morphology, structure, and capacitive properties of the carbon materials prepared using the molten salt strategy. Finally, the current research status of the preparation of carbon-based materials by the molten salt method is summarized, the shortcomings of existing technology are pointed out, and the prospects for its development are envisioned. It is hoped that this review can provide some basic knowledge for the preparation of carbon-based materials by the molten salt method and promote further research on molten salt technology. [ABSTRACT FROM AUTHOR]

The rapid developments of the Internet of Things (IoT) and portable electronic devices have created a growing demand for flexible electrochemical energy storage (EES) devices. Nevertheless, these flexible devices suffer from poor flexibility, low energy density, and poor dynamic stability of power output during deformation, limiting their practical applications. Carbon nanofibers (CNFs) with high conductivity, good flexibility, and large‐scale preparation are regarded as promising electrodes for flexible EES devices. Based on the issues of current flexible EES devices, this review presents various strategies from the design of CNFs‐based electrodes to the fabrication of devices and overviews their applications in various flexible metal ion/air batteries (Li/Na/K‐ion batteries, Li‐S batteries, metal–air batteries, and other novel secondary batteries) and supercapacitors. Finally, the remaining challenges and perspectives on the CNFs‐based flexible EES devices are proposed to provide guidance for the researchers concentrating on high‐performance flexible EES devices. [ABSTRACT FROM AUTHOR]

Herein, MnO2 nanoflowers are electrodeposited on a self-supported and electroconductive electrode in which 2D Ti3C2Tx nanosheets are encased in carbon nanofibers (MnO2@Ti3C2Tx/CNFs). This improves the conductivity and hydrophilicity of the MnO2 composite electrode. The asymmetric supercapacitor shows a high energy density of 46.4 W h kg−1 and a power density of 4 kW kg−1. [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs) are attracting a significant amount of interest as energy storage devices owing to their higher specific power, rapid charging–discharging rate, and prolonged cyclic stability. Carbon-based materials are used frequently in SCs because of their excellent electric conductivity, stable chemical properties, and low cost. Electrospun polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) have attracted much interest as they perform well electrochemically, have a large surface area, and show substantial mechanical characteristics; as well as having a high carbon yield among all polymer PAN. In this paper, an extensive review of the synthesis, characterization, and electrochemical performance of electrospun PAN CNFs is presented. An overview of the electrospinning procedure and properties of PAN CNFs that make them suitable for SC applications is presented. Various characterization methods, including transmission electron microscopy, scanning electron microscopy, x-ray diffraction, Raman spectroscopy, and surface area analysis, have been carried out to evaluate the morphological, structural, and surface properties of PAN CNFs. The review also highlights the recent advances in modification and functionalization to enhance their electrochemical performance, including doping, surface functionalization, and hybridization. Galvanostatic charge–discharge experiments, cyclic voltammetry, and electrochemical impedance spectroscopy have been employed for electrochemical characterization. Finally, a comparative study between various carbon-based and electrospun PAN CNF electrode materials for SCs has been conducted. The review is concluded by discussing the challenges, opportunities, and possible future trends in the development of high-performance electrode material. This comprehensive review provides valuable insightful information on the design and optimization of electrospun PAN CNF electrode materials for SC applications. [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]

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]

[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]

Printed electronic paper identifies its interest in flexible organic electronics and sustainable and clean energy applications because of its straightforward production method, cost‐effectiveness, and positive environmental impact. However, current limitations include restricted material thickness and the use of supporting substrate for printing. Here, 2D and 3D electronic patterned paper are fabricated from direct ink writing (DIW) nanocellulose and PEDOT:PSS‐based materials using syringe deposition and 3D printing. The conductor patterns are integrated in the bulk of the paper, while non‐conductive sections are used as support to form free‐standing paper. The strong interface between the patterns of electronic patterned paper gives mechanical stability for practical handling. The conductive paper‐based electrode has 202 S cm−1 and is capable of handling electric current up to 0.7 A, which can be used for high‐power devices. Printed supercapacitor papers show high specific energy of 4.05 Wh kg−1, specific power of 4615 W kg−1 at 0.06 A g−1, and capacitance retention above 95% after 2000 cycles. The new design structure of electronic patterned papers presents a solution for additive manufacturing of paper‐based composites for supercapacitors, wearable electronics, or sensors for smart packaging. [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]

Exploring anode materials with an excellent electrochemical performance is of great significance for supercapacitor applications. In this work, a N-doped-carbon-nanofiber (NCNF)-supported Fe3C/Fe2O3 nanoparticle (NCFCO) composite was synthesized via the facile carbonizing and subsequent annealing of electrospinning nanofibers containing an Fe source. In the hybrid structure, the porous carbon nanofibers used as a substrate could provide fast electron and ion transport for the Faradic reactions of Fe3C/Fe2O3 during charge–discharge cycling. The as-obtained NCFCO yields a high specific capacitance of 590.1 F g−1 at 2 A g−1, superior to that of NCNF-supported Fe3C nanoparticles (NCFC, 261.7 F g−1), and NCNFs/Fe2O3 (NCFO, 398.3 F g−1). The asymmetric supercapacitor, which was assembled using the NCFCO anode and activated carbon cathode, delivered a large energy density of 14.2 Wh kg−1 at 800 W kg−1. Additionally, it demonstrated an impressive capacitance retention of 96.7%, even after 10,000 cycles. The superior electrochemical performance can be ascribed to the synergistic contributions of NCNF and Fe3C/Fe2O3. [ABSTRACT FROM AUTHOR]

In this work, we reported the electrochemical performance of a type of carbon fabric-based supercapacitor by coating MnOx@rGO nanohybrids on carbon fabric with a simple one-step hydrothermal method. We studied the mass ratio of MnOx to rGO on the electrochemical properties of the carbon fabric-based supercapacitors. We found that as the mass ratio is 0.8:1 for MnO@rGO, the supercapacitor with a loading of 5.40 mg cm−2 of MnO@rGO nanohybrids on carbon fabric exhibits a specific capacitance of 831.25 mF cm−2 at 0.1 mA cm−2 current density. It also shows long-term cycling capacitance retention of 97.2% after 10,000 charge–discharge cycles at a current density of 0.4 mA cm−2. We speculate that the high electrochemical performance results from the strong interfacial bonding between the hierarchical architecture of MnO@rGO nanohybrids and carbon fabric. [ABSTRACT FROM AUTHOR]

The combination of multiple electrode materials and their reasonable structural design are conducive to the preparation of composite electrodes with excellent performance. In this study, based on carbon nanofibers grown with Ni(OH)2 and NiO (CHO) prepared by electrospinning, hydrothermal growth, and low-temperature carbonization, five transition metal sulfides (MnS, CoS, FeS, CuS, and NiS) were hydrothermally grown on their surfaces, exhibiting that CHO/NiS had the optimal electrochemical properties. Subsequently, the effect of hydrothermal growth time on CHO/NiS revealed that the electrochemical performance of CHO/NiS-3h was optimal, with a specific capacitance of up to 1717 F g−1 (1 A g−1), due to its multistage core–shell structure. Moreover, the diffusion-controlled process of CHO/NiS-3h dominated its charge energy storage mechanism. Finally, the asymmetric supercapacitor assembled with CHO/NiS-3h as the positive electrode demonstrated an energy density of 27.76 Wh kg−1 at a maximum power density of 4000 W kg−1, and it still maintained a power density of 800 W kg−1 at a maximum energy density of 37.97 Wh kg−1, exhibiting the potential application of multistage core–shell composite materials in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Porous carbon materials have demonstrated exceptional performance in various energy and environment-related applications. Recently, research on supercapacitors has been steadily increasing, and porous carbon materials have emerged as the most significant electrode material for supercapacitors. Nonetheless, the high cost and potential for environmental pollution associated with the preparation process of porous carbon materials remain significant issues. This paper presents an overview of common methods for preparing porous carbon materials, including the carbon-activation method, hard-templating method, soft-templating method, sacrificial-templating method, and self-templating method. Additionally, we also review several emerging methods for the preparation of porous carbon materials, such as copolymer pyrolysis, carbohydrate self-activation, and laser scribing. We then categorise porous carbons based on their pore sizes and the presence or absence of heteroatom doping. Finally, we provide an overview of recent applications of porous carbon materials as electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]

Fiber‐shaped supercapacitors (FSCs) have become one of the significantly strategical flexible energy‐storage materials towards future wearable textile electronics and metaverse technologies. Here, we develop the high‐performance FSCs based on multiscale dot‐wire‐sheet heterostructure microfiber of nitrogen‐doped carbon dots‐Ti3C2Tx/silk nanofibers (NCDs‐Ti3C2Tx/SNFs) hybrids via microfluidic fabrication. Due to the enlarged interlayer spacing, plentiful porous channels, accelerated H+ ion transport dynamics, large electrical conductivity and excellent mechanical strength/flexibility, the NCDs‐Ti3C2Tx/SNFs possesses high volumetric capacitance (2218.7 F cm−3) and reversible charge–discharge stability in 1 M H2SO4 electrolyte. Furthermore, the solid‐state FSCs present high energy density (57.9 mWh cm−3), good capacitance (1157 F cm−3), long‐life cycles (82.3 % capacitance retention after 40000 cycles), which realize the actual energy‐supply applications (powering lamp, watch and toy car). [ABSTRACT FROM AUTHOR]

Fiber‐shaped supercapacitors (FSCs) have become one of the significantly strategical flexible energy‐storage materials towards future wearable textile electronics and metaverse technologies. Here, we develop the high‐performance FSCs based on multiscale dot‐wire‐sheet heterostructure microfiber of nitrogen‐doped carbon dots‐Ti3C2Tx/silk nanofibers (NCDs‐Ti3C2Tx/SNFs) hybrids via microfluidic fabrication. Due to the enlarged interlayer spacing, plentiful porous channels, accelerated H+ ion transport dynamics, large electrical conductivity and excellent mechanical strength/flexibility, the NCDs‐Ti3C2Tx/SNFs possesses high volumetric capacitance (2218.7 F cm−3) and reversible charge–discharge stability in 1 M H2SO4 electrolyte. Furthermore, the solid‐state FSCs present high energy density (57.9 mWh cm−3), good capacitance (1157 F cm−3), long‐life cycles (82.3 % capacitance retention after 40000 cycles), which realize the actual energy‐supply applications (powering lamp, watch and toy car). [ABSTRACT FROM AUTHOR]

Summary: This paper focuses on the parameter identification issue of electrochemical double layer capacitors (EDLCs). The superiority of the fractional‐order equivalent impedance model is revealed mathematically and electrochemically by analyzing the variation trends of different models and the general electrochemical impedance spectroscopy (EIS) of EDLCs. Since the fractional‐order models can be used to describe the long‐tailed variation trend of the EIS of EDLCs in the low‐frequency band and can reflect the self‐charging phenomenon of EDLCs, the accuracy of parameter identification can be ensured. In addition, the idea of Levy flight is introduced and combined with the intelligent algorithms in the parameter identification process, thus accelerating the convergence rate of the parameter identification process. At the same time, the problem of nonconvex fitness function falling into local optimum can be solved. To confirm the effectiveness and superiority of this work, we provided diverse test scenarios. We used three different types of EDLCs, while a series of scenarios with or without Levy flight strategy were included in the tests. In our work, we compared not only the accuracy of the parameter identification but also the convergence rate of the identification process. The test results show that, by applying the proposed scheme, the sum of square error (SSE) between experiments and parameter identification results is less than 1.9%. Moreover, the convergence rate of the parameter identification process was improved. In extreme conditions, the convergence rate is 1287% faster than the schemes without Levy flight strategy. [ABSTRACT FROM AUTHOR]

Among various types of energy storage, the supercapacitor is regarded as the most promising device due to its long cycling life, good cycling stability, and high power density. A supercapacitor is generally composed of electrodes, electrolytes, and a separator. The separator is one of the most important components, serving to prevent internal short circuits between the anode and the cathode. Herein, a nanostructured-based separator in a PAN/PVDF nanofiber scheme is introduced for improving the electrochemical performance of the supercapacitor. Briefly, the membranes were produced via the electrospinning technique. All of the raw materials were blended in various compositions of PVDF for optimization purposes. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were carried out to identify the microstructure of the nanofibers. The electrochemical properties of the membrane were measured using galvanostatic charge-discharge (GCD). Based on GCD, it was shown that the PAN/PVDF 20 wt% membrane exhibited the optimum gravimetric capacitance at 54.104 Fg-1 as evidenced by a high porosity percentage. Thus, the PAN/PVDF nanofiber has good potential as a separator for application in supercapacitors. [ABSTRACT FROM AUTHOR]

Currently, lightweight wearable energy storage devices are in great demand owing to their use in wearable electronics and energy-efficient electric vehicles. Freestanding carbon nanofibers replace the need for metal substrates while providing a rapid electrical network owing to their excellent electrical properties. Bimetallic oxides with multivalent oxidation states facilitate the rapid transfer of electrolytic ions owing to efficient Faradaic reactions, thereby enhancing the overall energy storage capability. In this study, CoOx@CNF was derived from ZIF-67 (zeolitic-imidazolate framework) @PAN-2MI fibers that were stabilized in air at 280°C and then annealed in argon at 900°C. Subsequently, Co was seeded on the annealed CoOx@CNF and subjected to a hydrothermal process in sodium molybdate dihydrate solution to grow CoMoO4 nanosheets, eventually forming bimetallic CoMoO4@CNF. The concentration of sodium molybdate solution was varied to determine the optimal growth conditions for CoMoO4 nanosheets. The energy density of the optimal bimetallic CoMoO4@CNF sample was 166.5 μWh cm-2 at a power density of 200 μW cm-2; this represented a nearly twofold increase compared to that of the single metallic CoOx@CNF. Powering humidity sensors using only one CoMoO4@CNF supercapacitor was demonstrated. The optimal sample remained stable during long-term galvanostatic charge and discharge cycles ( N cyc = 30,000) and retained 100% of its specific capacitance. [ABSTRACT FROM AUTHOR]

Supercapacitors are considered as important energy conversion and storage devices, and one‐dimensional carbon nanofibers derived from electrospinning have been widely applied for supercapacitor electrode materials. The integration of carbon and metal hydroxide materials has become particularly important in order to pursue their higher electrochemical properties. In this paper, a one‐dimensional core‐shell electrode with Ni(OH)2 as shell and carbon nanofibers as core (Ni/CNFs@Ni(OH)2) was fabricated by electrospinning, high‐temperature carbonization and hydrothermal synthesis. This electrode exhibited high energy storage performance (785 F g−1 (1 A g−1)), good coulombic efficiency and cycling stability. Furthermore, the asymmetric supercapacitor (ASC) assembled with activated carbons as negative electrode and Ni/CNFs@Ni(OH)2 as positive electrode demonstrated a good energy storage performance (62.5 F g−1 (1.6 V)). Meanwhile, this ASC displayed a significant energy density of 22.2 Wh kg−1 at 800 W kg−1 and an outstanding rate capability, indicating that Ni/CNFs@Ni(OH)2 had a high potential application value in 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]

Enhancing the electrochemical performance while maintaining excellent mechanical properties of carbon nanofiber-based flexible electrodes remains a significant challenge, which blocks their potential application in advanced energy storage and conversion. Herein, taking advantage of the thermal stability difference between polyacrylonitrile and polypyrrolidone, we report a simple strategy to fabricate N-doped porous carbon nanofiber membranes with inter-fiber cross-linked structures via eccentric coaxial electrospinning combined with carbonization processes. During carbonization processes, the obstacles of large contact resistance are removed and sufficient contacts among electrospun nanofibers are formed, endowing the carbon nanofiber membranes with outstanding electrical conductivity (25.4 S cm−1) and flexibility in various forms. Further, NiCo 2 O 4 nanoneedles are in-situ decorated onto the prepared carbon nanofiber membranes to construct hybrid electrodes for improving capacitance. The hybrid electrodes (NiCo 2 O 4 @NPCNFs) achieve a competitive specific capacitance (capacity) of 1474.2 F g−1 (245.4 mAh g−1) at the current density of 0.5 A g−1, as well as good rate performance (78.0% capacitance retention at a current density of 10 A g−1). In addition, the assembled asymmetric supercapacitors exhibit a high energy density of 53.0 Wh kg−1. This study paves a promising way toward carbon nanofiber-based electrodes for application in energy storage systems. [Display omitted] • According to the different thermal stabilities of the polymers, cross-linked electrospun carbon nanofibers are prepared. • Design eccentric core-shell nanofibers to facilitate the outflow of the melting core to form abundant crosslinking points. • The novel carbon nanofiber membranes render robust flexibility and high electrical conductivity. • The assembled flexible supercapacitor can supply power stably and continuously even under severe bending states. [ABSTRACT FROM AUTHOR]

The development of advanced coal-based functional nanomaterials is of great significance for clean and effective utilization of coal resources. Herein, we report novel coal-based ultra-fine carbon nanosheets (UCNSs) prepared by chemical oxidation of bituminous coal with a high yield of 40.0 wt%. UCNSs show a lamellar size of 10–20 nm, mainly composed of 63.5 at.% carbon, 5.1 at.% nitrogen, and 31.4 at.% oxygen. The structural merits of suitable size distribution, enriched functional groups, and highly conjugated core enable the UCNSs showing a tri-functional reinforcement for carbon nanofibers prepared by electrospinning and carbonization. Thanks to the strong cross-linking effect and formation of entire conductive networks, the UCNS-embedded carbon nanofiber fabrics show 32.6 and 1.5 times improved mechanical strength and electrical conductivity, respectively, than the one without UCNSs. What's more, the exposed edges of UCNSs act as active sites for ultrafast capacitive energy storage, leading to the free-standing fabric with significantly improved capacitance and rate performance (191.2 F g−1 at 1 A g−1, 113.5 F g−1 at 50 A g−1) for aqueous supercapacitors. This work may provide a new thought for high-efficient and high-value-added utilization of coal resources. Ultra-fine carbon nanosheets with a high yield of 40.0 wt% were prepared through liquid-phase oxidation of bituminous coal, showing tri-functional (mechanical/electrical/electrochemical) reinforcement for carbon nanofiber fabrics. [Display omitted] • Ultra-fine carbon nanosheets with a high yield of 40 wt% were prepared from coal. • The inlaid UCNSs show tri-functional reinforcement for carbon nanofiber fabrics. • Exposed edges enable an ultra-fast pseudocapacitive energy storage ability. [ABSTRACT FROM AUTHOR]

The logical design and engineering of bimetallic oxide nanomaterials with porous carbon materials have had a significant impact on the development of high-performance electrode materials for energy storage devices in recent years. The vertical and uniform building of porous multimetal nanomaterials on the surface of nanoscale carbon fibers is difficult but not impossible. We present a self-templated metal-organic framework (MOF)-based strategy for the synthesis and assembly of bimetallic oxides/nanoporous carbon nanostructures (Ni–Fe–O/NPC) on porous carbon nanofibers (PCNFs). The vertical alignment of Ni–Fe–O/NPC at PCNFs favors a fast redox reaction by shortening the ion/electrode diffusion path at the electrode-electrolyte interface and helps enhance the overall electrochemical performance. As a freestanding electrode for supercapacitors, it has a high specific capacitance of 1419 F g−1 at 1 A g−1 and good cycling life with capacitance retention of approximately 88.5% after 10,000 cycles. The Ni–Fe–O/NPC@PCNFs-400//Fe 2 O 3 /NPC@PCNFs asymmetric supercapacitor (ASC) achieves a high energy density of 41.3 Wh kg−1 at a power density of 892.2 W kg−1 with a long cycle of life (20,000 cycles) and a high rate capability (78.6%), indicating its potential applications. [Display omitted] • MOF-derived metallic oxides on PCNFs as free-standing electrode materials for ASC. • Tetragonal rodlike Ni–Fe–O/NPC@PCNFs is successfully grown using Ni–Fe-MOF@PCNFs. • Vertical alignment of Ni–Fe–O/NPC at PCNFs provides sufficient redox-active sites. • The assembly of Ni–Fe–O/NPC@PCNFs//Fe 2 O 3 /NPC@PCNFs as an ASC delivers high energy density. [ABSTRACT FROM AUTHOR]

The booming demand for energy storage has driven the rapid development of energy storage devices such as supercapacitors, and the research on high-performance electrode materials, a key component of supercapacitors, has gained tremendous attention. In this research, phenolic resin-based multi-porous carbon nanofibers have been prepared by electrospinning, curing, carbonization and activation and then employed as advanced electrode materials in supercapacitors. We demonstrate that the material is nano-scale continuous fiber, and its surface has pore distribution of different sizes. It delivers a high specific capacitance of 242 F g−1 at a current density of 0.2 A g−1 and maintains 148 F g−1 even at a high current density of 20 A g−1. Moreover, it shows almost no capacitance decay at a current density of 2 A g−1 over 1000 cycles, demonstrating its great potential as high-performance electrodes in supercapacitors. [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]

Carbon nanofiber nonwovens (CFN) are powerful electrode materials with exceptional performance in energy storage devices, such as batteries and supercapacitors. Small fiber‐diameters together with hierarchical porosity endow CFN‐electrode materials with large surface areas and high electrical capacitance. Porosity of the fiber surface is often realized by corrosive activation methods such as wet‐etching or using oxidative gases at elevated temperatures. In this study, we present a chemical‐free, environmental‐friendly, and easily controllable surface activation method using an atmospheric pressure plasma‐jet. We investigate the best instant for activation along the process chain and show that the surface area of nanofiber nonwovens can be tailored by adjusting the plasma exposure‐dose. Plasma‐activated CFNs show an almost 20‐fold increase in capacitance (CspPJ = 10.1 F/g) in an electrochemical supercapacitor setup compared to nonactivated CFN (CspnoPJ = 0.55 F/g). [ABSTRACT FROM AUTHOR]

Transition−metal−based materials show great promise for energy conversion and storage due to their excellent chemical properties, low cost, and excellent natural properties. In this paper, through simple strategies such as classical electrospinning, air calcination, and the one−step hydrothermal method, a large area of Ni(OH)2 nanosheets were grown on NiMoO4 nanofibers, forming NiMoO4@Ni(OH)2 nanofibers. The one−dimensional nanostructure was distributed with loose nanosheets, and this beneficial morphology made charge−transfer and diffusion more rapid, so the newly developed material showed good capacitance and conductivity. Under the most suitable experimental conditions, the optimal electrode exhibited the highest specific capacitance (1293 F/g at 1 A/g) and considerable rate capability (56.8% at 10 A/g) under typical test conditions. Most interestingly, the corresponding asymmetrical capacitors exhibited excellent electrochemical cycle stability, maintaining 77% of the original capacitance. NiMoO4@Ni(OH)2 nanofibers were verified to be simple to prepare and to have good performances as energy−storage devices within this experiment. [ABSTRACT FROM AUTHOR]

One of the global problems is environmental pollution by different biowaste. To solve the problem, biowaste must be recycled. Waste-free technology is also a way of saving exhaustible raw materials. Research on electrochemical energy sources is currently the most dynamically developing area of off-grid energy. Electrochemical capacitors can operate for a long time without changing performance, they have smaller dimensions, high mechanical strength, and a wide operating temperature range. These properties are effective energy-saving devices. Therefore, supercapacitors are widely used in various industries. This review discussed the methods of obtaining and the characteristics of biowaste-derived activated carbon and carbon–manganese oxide (AC-MnO2)-based supercapacitor electrodes. [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]

Triple-layered boron-containing carbon nanofibers (CNFs) with hollow channels (PPMPB) are fabricated via step-by-step electrospinning for high-performance freestanding supercapacitors. Polyacrylonitrile (PAN)-based CNFs in the first layer are chosen as the support layer material because of their excellent chemical stability and electrospinnability. The well-developed hollow channels provided fast ion diffusion in the second layer of PAN/poly(methyl methacrylate) (PMMA)-based CNFs. The surface boron functional groups constituting the third layer contribute to the pseudo-capacitance. The symmetric supercapacitor of the PPMPB electrodes delivers a maximum specific capacitance of 180 Fg−1 at 1 mAcm−2, a high energy density of 22.38 Whkg−1 at a power density of 400 Wkg−1, and an excellent retention rate of 96% after 10,000 cycles in aqueous solution. The excellent electrochemical performance is attributed to the unique sandwich nanostructure with a three-layer structure, in which the factors representing the electrochemical properties of each layer do not interfere with each other. Therefore, a moderate amount of boron and the high surface area of the triple-layer structured PPMPB can be fully utilized as an excellent conductive network and electroactive sites, which is expected in a high-performance supercapacitor electrode. [Display omitted] • Triple-layered boron-containing CNFs were fabricated by step-by-step electrospinning. • The CNFs in the first layer provide active adsorption sites for EDLC. • Hollow core present in the interlayer serves as an excellent conductive network. • A moderate amount of boron in the third layer is utilized as the electroactive site. • Symmetric PPMPB(20) electrode showed good rate capability and long cycle life. [ABSTRACT FROM AUTHOR]

Highly graphitic porous carbon was derived from kelp biomass and prepared using KOH as the main activating agent with K2FeO4 as the assisting activated agent for supercapacitor applications. The optimum K2FeO4 mass in the total activating agent and temperature were investigated. The characterization results showed porous sheet carbon with a high specific surface area of 2868 m2 g−1 and a low ID/IG of 0.909. It delivered an excellent specific capacitance of 438 F g−1 at 0.5 A g−1. In addition, the assembled supercapacitor device reached the highest energy density of 19.9 W h kg−1 with a power density of 398 W kg−1. [ABSTRACT FROM AUTHOR]

Due to the unique geometric characteristics and electronic structure of hierarchical 3D nanosheets, they show excellent electron migration rate, ultra‐high specific surface area, and reliable structural stability. Therefore, 3D nanosheets have great application prospects in the field of electrochemical energy storage. Supercapacitor has attracted extensive attention in recent years due to its merits of fast charge and discharge, long cycle life, safety, and stability. Flexibility, miniaturization, and intelligent integration are the development direction of supercapacitor energy storage devices. The emerging 3D printing technology, especially the ink direct writing mode, has greatly improved the design ability and control accuracy of device microstructures. Based on the research progress of 3D graphene nanosheets and 3D MXene nanosheets in the early stage of the authors' or other teams, this paper proposes to use advanced 3D printing technology to realize the design of flexible all solid‐state supercapacitors by using 3D nanosheets active materials with high specific capacitance. The design methods of interdigital electrodes, multilayer skeleton electrodes and fiber electrodes by 3D printing technology and the performance evaluation of flexible supercapacitor are systematically analyzed. This perspective review aims to provide new conception and theoretical guidance for the design, preparation, and performance optimization of 3D nanosheets‐built materials by 3D printing for the practical application of flexible all‐solid‐state supercapacitor in the future. [ABSTRACT FROM AUTHOR]

The hurdle of fabricating asymmetric supercapacitor (ASC) devices using a faradic cathode and a double layer anode is challenging due to the required large amount of active mass of anodic material compared to that of the cathodic material during mass balancing due to the large difference in capacitance values of the two electrodes. Here, the problem is addressed by engineering a negative electrode that furnishes an ultrahigh capacitance. An in situ developed metal–organic framework (MOF)‐based thermal treatment is adopted to grow highly porous N‐doped carbon nanotubes (CNTs) containing submerged Co nanoparticles over nano‐fibrillated electrospun hollow carbon nanofibers (HCNFs). The optimized CNT@HCNF‐1.5 furnishes an ultrahigh capacitance approaching 712 F g–1 with excellent rate capability. The capacitance reported from this work is the highest for any carbonaceous material reported to date. The CNT@HCNF‐1.5 is further used to fabricate symmetric supercapacitors (SSCs), as well as ASC devices. Remarkably, both the SSC and ASC devices furnish incredible performances in all aspects of SCs, such as a high energy density, long cycle life, and high rate capability, displaying decent practical applicability. The energy density of the SSC device reaches as high as 20.13 W h kg–1, whereas that of ASC approaches 87.5 W h kg–1. [ABSTRACT FROM AUTHOR]

Designing SnO 2 /carbon composites is an effective strategy to improve the conductivity and buffer the volume expansion of SnO 2. However, it remains a challenge to combine SnO 2 and carbon materials tightly as a stable integration. Herein, a facile and versatile strategy of Sn/SnO 2 nanodots anchored tightly into carbon nanofibers (CNFs) with the decoration of graphene quantum dots (GQDs) for high performance supercapacitor is reported. Through a simple electrospinning and carbonization reduction process, a novel multidimensional carbon skeleton of GQD/CNF effectively improves the conductivity, and importantly, abundant Sn–O–C covalent bonds are constructed to anchor SnO 2 nanodots tightly into GQD/CNF, suppressing SnO 2 aggregation and facilitating electron/ion transfer kinetics. Consequently, as self-supporting and binder-free electrode material, Sn/SnO 2 /GQD/CNF displays high specific capacitance of 168.6 mA h g−1 (1349 F g−1) at 1 A g−1 with excellent rate capability (88.9% retention at 20 A g−1). Furthermore, a flexible solid-state asymmetric supercapacitor based on Sn/SnO 2 /GQD/CNF and GQD/CNF achieves a high energy density of 32.3 W h kg−1 at a power density of 800 W kg−1 with remarkable flexibility and cycling stability (86.1% retention after 5000 cycles). The excellent electrochemical performances demonstrate that this novel carbon skeleton anchored active materials shows great potential for electrochemical energy storage applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Nickel cobalt phosphide/carbon nanofibers (NiCoP/C) with an average diameter of approximate 200 nm are prepared by electrospinning combined with calcinations. Carbon nanofibers with an average pore size of 10.77 nm as conductive skeletons support the dispersed NiCoP nanoparticles with the size ranging from 20 to 80 nm, providing abundant reactive sites and facilitating the electrochemical reactions. The specific capacitance of NiCoP/C reaches 478 F g−1 at 2 A g−1 in a 3 M KOH electrolyte, showing superior electrochemical properties compared to its counterparts. After 5000 charge/discharge cycles at 10 A g−1, 99.99 % of initial specific capacitance is retained. In addition, an asymmetric supercapacitor assembled using NiCoP/C as positive electrode and activated carbon as negative electrode exhibits an energy density of 16.72 Wh kg−1 at a high-power density of 7250 W kg−1. Furthermore, the capacitance loss of the supercapacitor is only 0.04 % after 5000 cycles at 10 A g−1, which is mainly attributed to the enhanced stability of NiCoP nanoparticles owing to the assistance of carbon nanofibers as the skeleton. The synergistic effects of NiCoP nanoparticles and carbon nanofibers result in the boosted electrochemical performances. This study demonstrates the potential application of carbon nanofibers as conductive skeletons for nanostructured electrodes. • NiCoP/C nanofibers were prepared by electrospinning without the emission of PH 3. • Carbon nanofibers acted as skeletons and conductive channels for NiCoP. • Assembled NiCoP/C//AC supercapacitor achieved 16.72 Wh kg−1 at 7250 W kg−1. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • The vacancy-defective graphene sheets are constructed successfully through polyacrylonitrile thermally mediated. • Vacancy defects on graphene sheets can enhance electrons/ions transport kinetics • The assembled aqueous zinc-ion hybrid supercapacitors exhibit a high energy density and outstanding cycling stability. The electrochemical behavior of graphene sheets in energy storage system is closely related to its electronic structures. Specifically, structural vacancy defects can expose more active sites and enhance the electrochemical performance. However, it is still a challenging problem to realize valid defect regulation on improving the reaction kinetics of electrode materials. Herein, vacancy-defective graphene sheets were constructed through the thermal mediated method via intercalation of polyacrylonitrile nanofibers. The vacancy defects were generated from the NH 3 gas resulting from polymer decomposition at gradient carbonization temperature. The obtained composites of the graphene sheets and carbon nanofibers demonstrate that the vacancy defects benefit to charge transport, allowing more electrons to pass through the interlayered structure, and enhance the adsorption capacitance during the reversible electrochemical process. In addition, the as-assembled Zn ion hybrid supercapacitors exhibit a high energy density of 129.9 Wh kg−1 and outstanding cyclic stability (99.8 % after 10,000 cycling). The confined polymer-mediated thermal modification strategy can afford abundant vacancy defective sites and exhibit promising outlook for constructing high-performance graphene-based electrode materials for Zn ion hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

Schematic illustration of the preparation of porous carbons. [Display omitted] • The porous carbons with controllable architecture were fabricated by a dual-role KCl-assisted activation method. • KCl not only serves as an auxiliary template but also contributes to an enhancement in the melting of K 2 CO 3. • The prepared porous carbons possess well-developed pore structure and excellent electrochemical performance. • This work paves a path to prepare porous carbons via an environment-friendly and cost-effective route for supercapacitors. Preparation of high-performance electrode materials in a low-cost and simple way is of great significance for the application and development of supercapacitors. Herein, a dual-role KCl-assisted KOH activation method with low KOH consumption was employed to fabricate porous carbons with controllable architecture, using the coal liquefaction residue (CLR) as the raw material. It is indicated that KCl not only serves as an auxiliary template for pore-forming but also contributes to an enhancement in the melting of K 2 CO 3 , an intermediate of KOH activation, resulting in an improvement in the efficiency of KOH activation. As a consequence, the prepared samples possess highly developed pore structure even at a low KOH consumption, which endow them with excellent capacitive performance. The as-fabricated optimal porous carbon (LR-KPC-4) displays a maximum specific capacitance of 375 F g−1 at 0.5 A/g and superior rate capacity, which are much better than those of the porous carbon prepared without KCl. The fabricated symmetric supercapacitor shows a high specific capacitance of 256 F g−1 at 0.5 A/g, energy density of 8.9 Wh kg−1 at 125 W kg−1 and great cycling stability. This work demonstrates a facile strategy to efficiently convert CLR into porous carbons for high-performance supercapacitors. Meanwhile, it paves a promising way for value-added utilization of CLR. [ABSTRACT FROM AUTHOR]

Vanadium Nitride (VN) is attractive for energy storage due to its high conductivity (1.6 × 106 S/m) and specific capacitance (1350 F/g) but limited to alkaline electrolytes for redox. In contrast, V 2 O 3 is redox active but not very conductive. In these hybrids a mixture of VN and vanadium oxide (V 2 O 3) were encapsulated in electrospun carbon-nanofibers. A combination of VN and V 2 O 3 takes advantage of the high conductivity from VN and the redox activity from V 2 O 3. Additionally, having the vanadium encapsulated within the carbon can help with the stability as the electrolyte will not have direct interaction with the surface. These hybrids were made by in-situ nitridation of the encapsulated V 2 O 5 followed by ex-situ activation with carbon dioxide. The hybrids were characterized by XPS and Raman spectroscopy. Hybrids of VN/V 2 O 3 -CNF showed increased capacitance of 245 Fg−1 with energy and power densities of 70.2 Wh kg−1 and 1751 W kg−1 in ionic liquid electrolyte. The devices showed good cycle stability with ∼90 % retention after 10,000 cycles at a current density of 1 Ag−1. These findings highlight the potential of VN/V 2 O 3 -CNF hybrids as high-performance supercapacitor electrodes. The combination of high conductivity and redox activity, along with encapsulation within CNFs, opens promising avenues for advanced energy storage. [ABSTRACT FROM AUTHOR]

Developing high-performing and scalable electrode materials for supercapacitors and batteries has been of tremendous interest for the world's forthcoming clean and renewable energy transition. As a versatile material, Two-dimensional graphitic carbon nitride (g-CN) has been utilized in electrochemical energy storage (EES) applications due to its nitrogen-rich adsorption sites, cost-effective production, and tunable electronic structure. The electrochemical performance of pristine g-CN has been boosted by forming hybrid architectures with highly conductive carbon-based materials, such as graphene, reduced graphene oxide, carbon nanofibers, carbon nanotubes, and beyond (e.g., MXene). Using such heterogeneous compositions for EES applications has significantly increased in recent years. This study reviews the g-CN/carbon nanomaterial (CNM) hybrids, considering the dimensionality in nanomaterials, and underscores the influence of the material's dimensionality and the synthesis/fabrication routes. The effect of structural and physicochemical changes on the electrode's electrochemical performance after hybridization is presented comparatively. Besides, the comprehensive review outlines challenges and future improvements in g-CN/CNM hybrid materials for outstanding developments in energy storage systems. [Display omitted] • Graphitic carbon nitride (g-CN)/carbon nanomaterial (CNM) hybrids are reviewed for supercapacitor and battery applications. • The impact of the CNM-type on the hybrid electrode's performance is examined through a chemical and physical perspective. • An overview of how hybrid electrode synthesis affects ion/electron transport, surface area, and porosity is provided. • Design-oriented control of the physicochemical properties for enhanced electrochemical performance is exemplified. • g-CN/CNM nanoarchitectures are emphasized as electrode materials with the potential for easy scalability. [ABSTRACT FROM AUTHOR]

The synthesis of Laser-Induced Graphene (LIG) through the laser ablation process of carbon-containing materials is a rapid and scalable process which enables the production of graphene in a cost-effective manner. In recent years, metal oxide – graphene composite electrodes have gained a lot of importance due to their use in various Energy Storage Devices (ESDs). In our investigation, we manufacture composite electrodes of manganese dioxide (MnO 2) and LIG through a hydrothermal process and use it as electrodes in Flexible Supercapacitors. This method deviates from traditional procedures as it eliminates the requirement for binders in creating composite electrodes, given that MnO 2 can be directly deposited onto the LIG electrodes. The assembled all-Flexible Supercapacitor (FSC), featuring unique LIG-MnO 2 composite electrodes, showcased a remarkable areal capacitance of 66.5 mF cm−2 at 5 mV s−1 scan rate. The device also exhibited a very high areal energy density (2.3 mWh cm−2) and power density (19.7 mW cm−2) at 0.2 mA cm−2 current density. Also, 82 % capacitance retention was observed at the end of 2000 cycles and the device also exhibited a good flexibility during bending tests, as evidenced by an 80 % capacitance retention after 100 bending cycles. [ABSTRACT FROM AUTHOR]