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MXene-integrated N-doped cavity-interconnected porous carbon nanofibers flexible film with excellent energy storage performance was prepared by a non-pre-oxidation synthesis strategy combining electrospinning and metal–organic framework derivatization. [Display omitted] • The flexible carbon film is constructed by MXene-integrated N-doped cavity-interconnected porous carbon nanofibers. • The non-preoxidation synthesis strategy overcomes the MXene oxidation and active site loss caused by the flexible carbon film during the preparation process. • The flexible carbon film exhibits a high energy density of 26.2 Wh kg−1 at 500 W kg−1 and good capacitance retention (96.3 %) after 10,000 charge–discharge cycles. • This study develops an effective general strategy for the preparation of embedded carbon nanofiber flexible film. Although the flexible carbon film integrated with MXene has been proven to be a new generation of supercapacitor material with good energy storage prospects, the MXene oxidation and the lack of active sites during the preparation of the carbon film can lead to irreversible capacity loss. Herein, a flexible carbon film constructed by MXene-integrated N-doped cavity-interconnected porous carbon nanofibers was prepared by a non-pre-oxidation synthesis strategy combining electrospinning and metal–organic framework derivatization. This flexible carbon film overcomes the oxidation problem of MXene during the stabilization of polyacrylonitrile, and the derived porous structure of cavity interconnection exposes more active sites. Due to its unique structural characteristics and ideal chemical composition, this independent flexible carbon film exhibits significantly enhanced electrochemical performance as an electrode material for supercapacitors. It exhibits an energy density of 26.2 Wh kg−1 at a power density of 500 W kg−1, and a capacitance retention rate of 96.3 % after 10,000 charge–discharge cycles. This study provides a unique strategy for the preparation of high-performance flexible carbon films, and this technology can also be extended to other integrated CNF composites for the design of high-performance supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • MXene nanosheets incorporated hollow carbon nanofibers (MX/HCFs) are designed. • Flexible and conductive MX/HCFs are used to develop vanadium-doped CoP nanorods as a freestanding positrode for supercapacitors. • MOF-derived Co-CNT@CNF negatrode is prepared by a facile heat treatment method. • V-CoP@MX/HCF and Co-CNT@CNF present specific capacitances of 1896.8F g−1 and 405.5F g−1, respectively, at 1 A g−1. • V-CoP@MX/HCF//Co-CNT@CNF flexible ASC device achieves an energy density of 72.4 Wh kg−1 at a power density of 800.12 W kg−1. Novel architectural electrode materials that are freestanding and exhibit improved electrochemical performances in flexible asymmetric supercapacitors are urgently needed; however, designing these materials is challenging. Herein, a Ti 3 C 2 T X MXene-aligned hollow carbon fiber (MX/HCF) is engineered and vanadium-doped cobalt phosphide nanorod arrays are grown on it (V-CoP@MX/HCF) and applied for supercapacitor positrode. V doping modulates the surface structure and electronic environment of CoP nanorods grown over conductive and flexible MX/HCFs. As expected, the optimized V-CoP@MX/HCF exhibits a better electrochemical performance (1896.8 F g−1) than that of CoP@MX/HCF and CoP@HCF. For the negative electrode, zeolitic imidazolate framework-67 (ZIF-67) grown on electrospun polyacrylonitrile (PAN) fibers is converted to cobalt nanoparticle-encapsulated nitrogen-doped carbon nanotubes at carbon nanofibers (Co-CNT@CNF) by a simple heat treatment without the burden of external catalysts and reducing gases. The as-designed freestanding Co-CNT@CNF delivers a specific capacitance of 405.5 F g−1 with superior cycling stability. A flexible asymmetric supercapacitor (V-CoP@MX/HCF//Co-CNT@CNF) is designed that unveil remarkable electrochemical properties, such as a high energy density of 72.4 Wh kg−1 at 800.12 W kg−1 and good capacitance retention (91.4 %) after 10,000 charge/discharge cycles. Furthermore, the device can maintain a consistent performance regardless of the bending degree. More importantly, this work provides new opportunities to rationally design novel freestanding cathodes and anodes for high-performance flexible asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]

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

[Display omitted] • Ti 3 C 2 T x MXene integrated hollow carbon nanofiber coated with outside inside polypyrrole layers (PPy@MXHCNF) is designed. • ZnCoMOF grown over PPy@MXHCNF is used to develop freestanding cathode (ZCO@PPy@MXHCNF) and anode (NPC@MXHCNF) materials. • ZCO@PPy@MXHCNF and NPC@MXHCNF exhibit specific capacitance of 1567.5 F g−1 and 477.21F g−1, respectively. • The assembled flexible ASC device delivers an energy density of 61.3 Wh kg−1 at 796.8 W kg−1. Effective customization of Ti 3 C 2 T x MXenes by electrospinning technique is crucial for the preparation of freestanding/flexible electrodes exhibiting enhanced performance in supercapacitors. Herein, we prepared MXenes containing hollow carbon nanofibers (MXHCNF) by co-axial electrospinning, and the inside-out of MXHCNF is decorated with polypyrrole layers (PPy@MXHCNF), which is sufficiently flexible, conductive, and highly functionalized with a unique trilayer morphology. Using the self-designed electroactive PPy@MXHCNF, a ZnCoMOF is homogeneously grown. The as-prepared bimetallic MOF on PPy@MXHCNF is used as a common precursor with which to fabricate the positive (ZCO@PPy@MXHCNF) and negative (NPC@MXHCNF) electrodes by a controlled heat treatment process using a "two from one" strategy. The freestanding positive and negative electrodes provide specific capacitances of 1567.5 F g−1 and 477.2 F g−1 at 1 A g−1, respectively, with high capacitance retention, cyclic stability, and coulombic efficiency. A flexible asymmetric device (ZCO@PPy@MXHCNF//NPC@MXHCNF) is assembled, and it exhibits an energy density of 61.3 Wh kg−1 at a power density of 796.8 W kg−1 and 92.8% capacitance retention after 10,000 GCD cycles. This work provides a unique approach involving MXene modification, polypyrrole decorated electrospun MXHCNFs as efficient substrates for freestanding electrodes, and the use of bimetallic MOF as a common strategic route for both positive and negative electrodes in flexible asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel nanohaired 3D cobalt hydroxide wheels have been uniformly inserted in CNFs. • Growth process of 3D cobalt hydroxide wheels in CNFs has been proposed. • 3D Co(OH) 2 /CNFs//NGH ASC exhibits high energy density with remarkable cycle life. Abstract Engineering nanostructures in the desired design and suitable size is one of the key issues for persuading high-performance supercapacitors (SCs). In this work, we report a successful synthesis of a new type of nanohaired three-dimensional cobalt hydroxide wheels/carbon nanofibers (3D Co(OH) 2 /CNFs) composite by a cost-effective electrospinning cum hydrothermal method. The 3D Co(OH) 2 wheels are composed of many partially-fused, nanohaired and serrated sheet-like nanoleaflets furnishing abundant active sites. This novel architecture is quite significant for the stability of the composite since the wheels encircle one or more conductive CNFs firmly rather than the simple attachment on the surface of substrate. The growth process of 3D Co(OH) 2 wheels on CNFs has been studied by synthesizing other two novel Co(OH) 2 /CNFs composites. The as-prepared material exhibits a specific capacitance of 1186 F g−1 at a current density of 1 A g−1 with excellent cyclic stability which is the highest reported value for Co(OH) 2 /CNFs composites. The asymmetric supercapacitor (ASC) device assembled using 3D Co(OH) 2 /CNFs as a positive electrode and nitrogen doped graphene hydrogel (NGH) as a negative electrode exhibits a high energy density of 60.31 W h kg−1 at power density of 740.8 W kg−1 which still remains 37 W h kg−1 even at a higher power density of 7500 W kg−1 with remarkable cycle life. Therefore, the composite stands as a promising candidate for SCs electrode material. This unique nanoengineering gives an insight into the synthesis of other stable nanocomposites for diverse applications like sensors, catalysis, etc. [ABSTRACT FROM AUTHOR]

Highly flexible freestanding carbon nanofibers were electroplated with silver for use in supercapacitor applications. The brittle carbon nanofibers were encased within bendable silver shells to provide superior flexibility and resilience of the supercapacitors. The enhanced electrical conductivity derived from the silver shell structure dramatically increased the capacitance of the supercapacitor. The silver shell also conferred structural stability to the carbon core, thus furnishing stable, long-term electrode performance. Nearly 100% of the specific capacitance was retained after N  = 10,000 galvanostatic charge-discharge cycles. The mechanical endurance or stability of the fabricated electrode was evaluated using 1,000 bending cycles, demonstrating that the electrode performance remained unchanged. Cyclic voltammetry and galvanostatic discharge curves were measured at various scan rates and current densities. The fabricated electrodes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, which clearly illustrated the carbon-core and silver-shell structure. [ABSTRACT FROM AUTHOR]

The development of new advanced nanostructures based on the hybridization of different carbon nanomaterials to obtain enhanced performance of energy storage devices has attracted considerable attention. Herein, a hierarchical nanostructure of carbon nanotubes supported electrospun carbon nanofiber networks (CNTs@CNFs) was successfully fabricated by using two facile techniques: – electrospinning and chemical vapor deposition (CVD). Such CNTs@CNFs hybrid showed the uniform and high density of CNTs directly grown on the surface of carbon nanofiber networks, leading to the formation of a hierarchical nanostructure with a large surface area and highly porous characteristics. The enhanced interactions between the CNTs and the CNFs networks were found to improve the electrical conductivity and electrochemical stability of the material. Owing to its unique nanoarchitectures and physicochemical properties, the CNTs@CNFs hybrid was demonstrated to be a potential electrode material for an electrochemical capacitor, in which a high specific capacitance of 464.2 F g −1 at 0.5 A g −1 and long-term stability with 97% retention after 10,000 repeated charge–discharge cycles were achieved. The obtained results suggest that the present CNTs@CNFs hybrid is a promising candidate for an electrochemical capacitor in energy storage technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • The active sites-rich Ni-Co-P@C/Ni-B material enables fast transfer of electron/ion. • DFT results verify stable OH* adsorption energy and metallic nature of the hybrid. • The Ni-Co-P@C/Ni-B shows a high specific capacity of 306 mAh g−1 at 3 mA cm−2. • Highly porous N-doped C nanofibers with nanocages was made as negative electrode. • The hybrid supercapacitor device shows 68.3 Wh kg−1 energy density at 472 W kg−1. In recent times, a lot of research effort has been performed to develop hybrid supercapacitors (HSCs) because of their ability to produce high energy density as well as superb power density. The key issue for realizing high-performance HSCs is to minimize the kinetic mismatch between rapid capacitor-type anode and sluggish battery-type cathode. Optimizing the interface, morphology and microstructure of the electrode material is a favorable approach to surmount kinetic imbalance. Herein, a core–shell nanoarrays of ultrathin carbon layer-coated crystalline Ni-Co-phosphide (Ni-Co-P@C) and amorphous Ni-boride (Ni-B) is fabricated on a nickel foam substrate as a positive electrode material (Ni-Co-P@C/Ni-B). Theoretical analyses validate the best metallic characteristic and most stable OH* absorption energy for Ni-Co-P@C/Ni-B, which enhance its charge storage performance than analogous Ni-Co-P and Ni-Co-P/Ni-B. The porous nitrogen (N)-doped carbon (C) nanofibers consisting of tightly embedded metal–organic framework (ZIF-8)-derived interconnected N-C nanocages (HP-N-CFs) showed excellent charge storage kinetics as a negative electrode. The battery-type Ni-Co-P@C/Ni-B electrode revealed a specific capacity of 306.2 mA h g−1 at 3 mA cm−2, while highly porous capacitive HP-N-CFs electrode showed the highest capacity of 56 mA h g−1 at 2.5 mA cm−2. In addition, the assembled quasi-solid-state (Ni-Co-P@C/Ni-B//HP-N-CFs) HSCs exhibited the highest energy density of 68.3 W h kg−1 at a power density of 472 W kg−1 with a superb rate capability (68% at 50 mA cm−2) and decent cyclic durability (90% retention over 10,000 cycles). [ABSTRACT FROM AUTHOR]

A freestanding, binder-free carbon nanofibers@polypyrrole@reduced graphene oxide (CNFs@PPy@rGO) core-double-shell supercapacitor electrode is prepared by carbonization of electrospun PAN nanofibers network follow by the electrochemical deposition of PPy and then reduced graphene oxide layer coating. The flexible all-solid-state supercapacitor based on the CNFs@PPy@rGO core-double-shell electrode with PVA/H 3 PO 4 gel electrolyte demonstrates a highest specific capacitance of 188 F/g at the scan rate of 2 mV/s and good cycling stability. Due to the synergistic effect of three materials, the newly designed composite electrode shows the highest specific capacitance of 336.2 F/g at the scan rate of 2 mV/s, which increases by 10% than that of CNFs@PPy electrode (302.7 F/g) at the same scan rate in a three-electrode system. Furthermore, it shows excellent cycling stability performance with 98% capacitance retention after 2500 cycles, which is better than that of CNFs@PPy electrode (90%). [ABSTRACT FROM AUTHOR]

Mesoporous carbon nanofibers (MCNFs) were prepared by electrospinning, carbonization and pickling process using phenolic resin as carbon source, pluronic F127 and Mg(NO 3 ) 2 ·6H 2 O as dual template. The obtained samples contained numerous oriented and parallel-to-fiber-axised mesopores and presented a specific surface area of 674 m 2 g −1 as well as high mesoporosity of 95%. The MCNFs were directly cut into electrodes free of binder for supercapacitors and tested in 6 M KOH electrolyte. In three-electrode system, the MCNFs showed a high specific capacitance (270 F g −1 at 0.2 A g −1 ) and outstanding rate performance (186 F g −1 at 20 A g −1 ). In two-electrode cell, the MCNFs presented a high capacitance of 160 F g −1 (86% of value at 0.1 A g −1 ) and excellent cycling stability (95% of capacitance retention after 5000 cycles). The free-standing nature and outstanding capacitance made the MCNFs a good candidate as electrode materials for next-generation flexible supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bi-metallic MOF-derived (Ni-Fe)-P-C@HCNFs and Fe P C@HCNFs are obtained as positive and negative electrodes of ASC. • Co-existence of redox-active bi-metallic phosphide at the inside and outside of HCNFs improves redox kinetics. • The (Ni-Fe)-P-C@HCNFs showed a high specific capacitance of 1392 F g−1 at 1 A g−1. • As fabricated ASC device shows a maximum energy density of 62.7 W h kg−1 at 8.23 kW kg−1 of power density. Bi-metallic metal–organic framework (MOF) generated phosphides within and outside the hollow carbon nanofibers (HCNFs) show remarkable potential for energy storage owing to their improved conductivity and high specific capacitance. A novel approach is used to synthesize (Ni-Fe)-P-C on the outer and inner surfaces of HCNFs. The synthesized material's substantial electrochemical performance is owing to the co-existence of numerous Ni and Fe-based redox-active species with porous carbon and open channels from MOF-derived Carbon at HCNFs for fast electrolyte ions/electron diffusion. Consequently, the (Ni-Fe)-P-C@HCNFs electrode has a high specific capacitance of 1392 F g−1 at 1 A g-1 and good cycling stability, with capacitance retention of approximately 89 % at 25 A/g. Moreover, after 10,000 cycles, the asymmetric supercapacitor (ASC): (Ni-Fe)-P-C@HCNFs//Fe P C@HCNFs has an optimal energy density of 62.7 Wh kg−1 and a power density of 8238.2 W kg−1, with cycling stability of 92.4 percent at a high current density of 25 A g-1. [ABSTRACT FROM AUTHOR]

• Co-MOF structures were anchored on the flexible MX-CNF. • Co-PC@MX-CNF and MnO 2 @Co 3 O 4 -PC@MX-CNF electrodes were derived from Co-MOF@MX-CNF. • A flexible and wearable hybrid supercapacitor was assembled using these electrodes. • The device shows an energy density of 72.5 Wh kg−1 at 832.4 W kg−1. Freestanding and flexible electrodes are crucial for advancing flexible and wearable energy storage devices (FW-ESD). However, the significant trade-off between mechanical flexibility and electrochemical performance of electrodes limits the development of high-performance FW-ESD. Therefore, flexible and freestanding multi-component hybrid electrodes with improved electrochemical properties are in high demand. This work reports a rational design of cobalt-metal organic framework (Co-MOF) structures on a highly flexible and electroconductive MXene-carbon nanofiber mat (MX-CNF). Further, the Co-MOF@MX-CNF was used as a starting material to derive capacitive-type Co-PC@MX-CNF and battery-type MnO 2 @Co 3 O 4 -PC@MX-CNF functional multi-component electrodes for a high-performance flexible wearable hybrid supercapacitor (FW-HSC). Owing to their high specific surface area (SSA), wettability, conductivity, and abundant active sites, Co-PC@MX-CNF and MnO 2 @Co 3 O 4 -PC@MX-CNF exhibited a specific capacitance of 426.7 F g−1 and a specific capacity of 475.4 mAh g−1 at 1 A g−1, respectively, with excellent mechanical flexibility. Moreover, the two electrodes were used to fabricate an FW-HSC with an operating voltage window of 1.5 V, delivering an energy density of 72.5 Wh kg−1 at a power density of 832.4 W kg−1 with long-term stability (90.36 % capacitance retention). Furthermore, a series connection of two identical FW-HSC devices could power a digital clock and light up a green LED, demonstrating its potential as a power source for various wearable devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • The fancy carbon nanofibers (CNFs) were prepared via coaxial electrospinning and carbonization. • The CNFs featured hollow and hierarchical porous structure. • The bridging structure formed by the carbon nanotubes (CNTs) endowed the CNFs with outstanding flexibility. • The CNFs decorated with polyaniline showed good electrochemical performance. • The assembled device could successfully power the electronics. Supercapacitors are considered to be the next generation of wearable energy storage devices because of reliable safety, high power density, and long cycle life, but the flexibility and energy density limit their practical applications. Herein, the flexible hollow hierarchical porous carbon nanofibers bridged by carbon nanotubes (HPCNFs@CNTs) are designed and constructed, followed by polyaniline (PANI) decorating to fabricate PANI@HPCNFs@CNTs. The synergistic effect of the hollow structure, hierarchical pores, in-situ nitrogen doping, and the bridging structure endows the HPCNFs@CNTs with a high specific capacitance of 461.0F g−1 (207.4 mF cm−2) while maintaining glorious flexibility under various deformation states. Besides, PANI@HPCNFs@CNTs possesses a high specific capacitance of 629.1F g−1 (405.2 mF cm−2) and remarkable cycle stability with 88.5 % capacitance retention after 5000 charging-discharging cycles. The device assembled by PANI@HPCNFs@CNTs renders an ultra-high energy density of 23.3 Wh kg−1 at a power density of 202.7 W kg−1. Furthermore, the device provides remarkable cycle stability and high-rate capability with a capacity retention of 91.3 % after 5000 cycles at 5 A g−1 and 76.7 % at 10 A g−1, respectively, demonstrating a tremendous potential to construct high-performance flexible energy storage devices. [ABSTRACT FROM AUTHOR]

Highlights: [•] Porous carbon nanofiber paper was prepared by surface chemical etching. [•] Specific surface area and surface functionality were greatly increased. [•] Carbon nanofiber paper had high specific capacitance of 362Fg− 1. [•] High power density, energy density and good cycling stability were combined. [•] The carbon paper can find applications in desalination, absorption and catalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A ternary ZnMgAl-LDH@Fe 2 O 3 /3DHPCNF were successfully prepared. • The electrode showed excellent electrochemical activity as both anode and cathode. • The structural and electrochemical effect of Zn has been studied in detail. • The optimized ZnMgAl-LDH@Fe 2 O 3 /3DHPCNF has yielded capacity of 3437 mF cm−2. • The supercapacitor device delivered high energy density of 11.622 mW cm−3 at 9.999 mW cm−3. Nano confinement of Layered double hydroxide (LDHs) nanosheets and metal oxide is a compelling way to develop new functional materials with unique physiochemical features for various energy storage devices with enhanced performance. Herein, ternary zinc-magnesium-aluminum layered double hydroxide (ZMA-LDH) nanosheets and hematite (α-Fe 2 O 3) nanorods are confined in a hetero-interfacial orientation on electrospun three-dimensional hollow and porous carbon nanofibers (3DHPCNF) by a subsequent hydrothermal process, resulting in the formation of a multi-dimensional nanoarchitecture. Such a structure can incorporate a conductive matrix and eliminate the need of current collectors, thereby minimizing the dead mass in electrochemical energy storage materials. The amount of Zn significantly determines the structural, morphological, and electrochemical properties of ZMA-LDH nanostructures. ZMA-LDH@Fe 2 O 3 /3DHPCNF was used as a free-standing electrode material for supercapacitors and endowed high capacitive behavior at both positive and negative working potentials. With the well-arranged 1D-3D hollow and porous interconnection, increased terrestrial surface area, and superior electrical conductivity, the hierarchical composite electrode offers a high areal capacitance of 3437F cm−2 at 1 mA cm−2 and ultrahigh cyclic stability. This fascinating electrochemical performance is attributed to the synergistic effect of 1D/2D/3D hollow and porous nanostructures, bimetallic compositions, top-to-bottom utilization of electrode materials, and unique combinations of surface interfacial diffusion and faradaic reduction governed by carbon and LDH/Fe 2 O 3 , respectively. Furthermore, a flexible all solid-state ZMA-LDH@Fe 2 O 3 /3DHPCNF symmetric supercapacitor exhibited a high areal energy density at a high power density along with excellent cyclability. This result suggests new prospects to design highly efficient multi material based electrodes for energy storage devices. [ABSTRACT FROM AUTHOR]

Highlights: [•] A facile spinning-based process was reported as novel nanofiber yarn fabricating method. [•] Aligned polyacrylonitrile precursor nanofiber yarn was prepared using the process. [•] Carbon nanofiber yarn (CNFY) was prepared as one-dimensional supercapacitor electrode. [•] The CNFY electrode possessed high conductivity, large specific capacitance and perfect cyclic performance. [ABSTRACT FROM AUTHOR]

• Flexible supercapacitors were fabricated using Ni-electroplated carbon nanofibers with NiGa 2 S 4 nanosheets. • The impact of the Ni/Ga ratio on the electrochemical performance of the supercapacitor was studied. • The NiGa 2 S 4 nanosheets promoted electrolyte diffusion and intensified the charge transport rate. • The specific capacitance was the highest at 488F·g−1 at a current rate of 0.5 A·g−1. Herein, high-power flexible supercapacitor electrodes were fabricated by decorating Ni-electroplated carbon nanofibers (Ni@CNF) with two-dimensional NiGa 2 S 4 nanosheets. The electrical conductivity of carbon nanofibers was enhanced by the addition of nickel, and the energy storage capability was enhanced by decoration with NiGa 2 S 4. The impact of metal (Ni/Ga) ratio on the overall electrochemical performance of the supercapacitor was studied by varying the Ga concentration. The NiGa 2 S 4 nanosheets promoted diffusion of the electrolyte into the electrode, thereby improving the electrochemical activity. The nanosheets also intensified the charge transfer rate within the composite electrode, which contributed to the overall improvement in the electrochemical performance. The optimal Ga concentration was the concentration at which the specific capacitance was the highest at 488 F·g−1 with a potential window of 1.1 V and current rate of 0.5 A·g−1. The long-term stability test revealed that the capacitance retention of the electrode with this optimal Ni/Ga ratio was 109% after 20,000 cycles. This flexible supercapacitor electrode was subjected to 2000 bending cycles, and the corresponding cyclic voltammetry performance was assessed. In combination, the outstanding electrochemical performance and durable mechanical properties render the NiGa 2 S 4 /Ni@CNF electrode highly suitable for flexible energy storage applications. [ABSTRACT FROM AUTHOR]

• Flexible supercapacitors were fabricated using Ni-electroplated carbon nanofibers with NiGa 2 S 4 nanosheets. • The impact of the Ni/Ga ratio on the electrochemical performance of the supercapacitor was studied. • The NiGa 2 S 4 nanosheets promoted electrolyte diffusion and intensified the charge transport rate. • The specific capacitance was the highest at 488F·g−1 at a current rate of 0.5 A·g−1. Herein, high-power flexible supercapacitor electrodes were fabricated by decorating Ni-electroplated carbon nanofibers (Ni@CNF) with two-dimensional NiGa 2 S 4 nanosheets. The electrical conductivity of carbon nanofibers was enhanced by the addition of nickel, and the energy storage capability was enhanced by decoration with NiGa 2 S 4. The impact of metal (Ni/Ga) ratio on the overall electrochemical performance of the supercapacitor was studied by varying the Ga concentration. The NiGa 2 S 4 nanosheets promoted diffusion of the electrolyte into the electrode, thereby improving the electrochemical activity. The nanosheets also intensified the charge transfer rate within the composite electrode, which contributed to the overall improvement in the electrochemical performance. The optimal Ga concentration was the concentration at which the specific capacitance was the highest at 488 F·g−1 with a potential window of 1.1 V and current rate of 0.5 A·g−1. The long-term stability test revealed that the capacitance retention of the electrode with this optimal Ni/Ga ratio was 109% after 20,000 cycles. This flexible supercapacitor electrode was subjected to 2000 bending cycles, and the corresponding cyclic voltammetry performance was assessed. In combination, the outstanding electrochemical performance and durable mechanical properties render the NiGa 2 S 4 /Ni@CNF electrode highly suitable for flexible energy storage applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hybrid film is prepared by a facile and patternable vacuum-filtration method. • The hybrid film is porous, conductive, ultrathin, and flexible. • The fabricated supercapacitors can withstand an ultrahigh scan rate of 500 mV s−1. • A large areal specific capacitance of 143 mF cm−2 is achieved at 0.1 mA cm−2. Traditional porous carbon (PC)-based supercapacitors (SCs) are generally stiff and heavy owing to their rigid components and bulky additives, such as binders, conducting materials, and current collectors. Herein, a porous (574.5 m2 g−1), conductive (83.1 S cm−1), and flexible MXene (Ti 3 C 2 T x)/cellulose nanofiber (CNF)/PC hybrid film is prepared by strong interfacial interactions among its components via a facile vacuum-filtration method. Three-dimensional PC provides abundant micropores for charge storage and considerable amount of meso/macropores for fast diffusion of ions. Two-dimensional Ti 3 C 2 T x offers a significantly high conductivity of 2.6 × 103 S cm−1 and a good film-forming ability. A one-dimensional CNF ensures high mechanical properties with a tensile strength of 38.6 MPa for the hybrid film by binding the adjacent Ti 3 C 2 T x flakes and PC. Additionally, the presence of CNF and PC increases the interlayer distance between Ti 3 C 2 T x flakes, thereby providing more ion-accessible surface areas on Ti 3 C 2 T x and creating open gaps for fast ion transport. Benefiting from these electrochemically attractive properties, this film is further employed as a free-standing electrode to fabricate a high-performance quasi-solid-state SC, which demonstrates an ultrathin thickness of 0.2 mm, a high flexibility, a significantly high areal capacitance of 143 mF cm−2 at 0.1 mA cm−2, and a large areal energy density of 2.4 μWh cm−2 at 17.5 μW cm−2, with a high retention of ~50% even after increasing the power density by ~100 fold. This work will pave the way for developing free-standing MXene-based hybrid films that simultaneously possess excellent conductivity, good mechanical properties, and large charge storage capacity for flexible and high-performance SCs. [ABSTRACT FROM AUTHOR]

A flexible membrane electrode by embedding vanadium/cobalt oxides on carbon nanofibers is purposely designed and fabricated by electrospinning and controllable post-calcination, which can be directly used as the binder-free non-polarity electrodes for the assembly of asymmetric solid-state supercapacitor with extraordinarily high areal metrics. • Vanadium/cobalt oxides embedded on carbon nanofibers (VCO/CNFs) are fabricated. • The integration of V promotes the formation of CoO and boosts electroactivity. • VCO/CNFs can be used as binder-free non-polarity membrane electrodes. • VCO/CNFs yield superior areal metrics and flexibility as supercapacitor electrodes. For flexible capacitive energy storage units in wearable devices, areal metrics, such as areal capacitance and energy density, are exceptionally important, because of limitations on device volume and weight. One-dimensional carbon nanofibers composited with active metal oxides, such as cobalt monoxide (CoO), possess extraordinary electrochemical properties. However, low areal metrics and the polarity in the flexible asymmetric supercapacitor device are two crucial challenges. Herein, vanadium/cobalt oxides on carbon nanofibers (VCO/CNFs) are purposely designed and fabricated by electrospinning and controllable post-calcination, which can be used as a binder-free non-polarity membrane electrode for the assembly of high-performance flexible supercapacitor (FSC). Importantly, the rational incorporation of vanadium with varying valence states helps promote the formation of CoO phase, enriches the reaction sites and enhances the capability of local electron transport. As expected, the single electrode of VCO/CNFs yields an extraordinarily high areal capacitance of 1.83 F cm−2 at the current density of 8 mA cm−2. The as-obtained FSC with VCO/CNFs as both anode and cathode delivers an excellent areal energy density of 44.2 μWh cm−2 at a power density of 2.8 mW cm−2, a long-term cycling stability (retention rate of 95.2% over 10,000 cycles), and a good flexibility under even various bending conditions. To our best knowledge, these areal metrics are among the superior values reported. [ABSTRACT FROM AUTHOR]

• Ultrathin in-plane 1T-2H MoS 2 heterostructures are coaxially arrayed on 3D CFs. • The 1T-2H ultrathin heterostructures exhibit surprising structure stability. • Our ASC device exhibits an ultrahigh energy density of 81.4 Wh kg−1. Metallic 1T MoS 2 is a promising anode candidate for supercapacitors due to its intrinsically excellent electrical conductivity and high electrochemical activity. However, it is quite unstable and hard to be massively synthesized through common methods. Herein, structurally stable ultrathin (1–3 layers) in-plane 1T-2H MoS 2 heterostructures have been rationally modulated and coaxially aligned on three-dimensional carbon nanofibers (MoS 2 /CF) through a facile hydrothermal approach for supercapacitors and electrocatalysis. Benefiting from the unique heterostructure, the MoS 2 /CF composite shows amazing stability with no obvious change after being stored in air for over 36 months. In addition, it presents high specific capacitance of 310 F g−1 and remarkable rate capability of 78% at 100 mV s−1. The fabricated asymmetric supercapacitor delivers an impressive energy density of 81.4 Wh kg−‍‍‍‍‍1 in 1 M Na 2 SO 4 solution attributed to the high specific capacitance and large operating voltage range of 2 V. Moreover, the MoS 2 /CF composite also demonstrates enhanced electrocatalytic activity for hydrogen evolution reaction with a low overpotential of 194 mV at 10 mA cm−2. The work may promote the developments of high-performance bifunctional energy conversion and storage systems in future. [ABSTRACT FROM AUTHOR]