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[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]

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]

• 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]

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]

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]