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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]

[Display omitted] • PVP/ZIF-7/PAN nanofibers carbonized at 900 °C yielded flexible ZnO P /C. • A capacitance of 382.5 mF cm−2 was obtained at a current density of 1 mA cm−2. • ZnO P /C demonstrated a capacitance retention of ∼ 101 % over 10,000 cycles. • ZnO P /C delivered an energy density of 49 μWh cm−2 at a power density of 2 mW cm−2. This study investigates the carbonization of electrospun fibers derived from zeolitic imidazolate framework (ZIF)-7/polyacrylonitrile solutions containing urea or polyvinylpyrrolidone (PVP). The carbonization yields highly flexible composites comprising nitrogen-doped carbon nanofibers and ZnO. Notably, using PVP as a nitrogen source generates a composite exhibiting excellent electrochemical performance. Specifically, it delivers a high capacitance of 382.5 mF cm−2 at a current density of 1 mA cm−2. Furthermore, this composite demonstrates capacitance retentions of approximately 101 % and 80 % after 10,000 cycles and a 90° bending test, respectively. The charge-storage capability of the PVP-based ZnO P /C composite surpasses that obtained without PVP by 1.4 times. Additionally, a composite fiber mat of ZnO P /C obtained via one-step electrospinning exhibits exceptional electrical conductivity and an energy density of 49 μWh cm−2 at a power density of 2 mW cm−2. These findings highlight the potential of this material as an electrode for supercapacitors. [ABSTRACT FROM AUTHOR]

The increasing commercialization of flexible electronic products has sparked a rising interest in flexible wearable energy storage devices. Supercapacitors are positioned as one of the systems with the most potential due to their distinctive advantages: high power density, rapid charge and discharge rates, and long cycle life. However, electrode materials face challenges in providing excellent mechanical strength while ensuring sufficient energy density. This study presents a method for constructing a flexible composite electrode material with high capacitance and mechanical performance by electrochemically depositing high-quality manganese dioxide (MnO 2) onto the surface of a nanocellulose (CNF) and carbon nanotube (CNT) conductive film. In this electrode material, the CNF/CNT composite film serves as a flexible conductive substrate, offering excellent mechanical properties (modulus of 3.3 GPa), conductivity (55 S/cm), and numerous active sites. Furthermore, at the interface between MnO 2 and the CNF/CNT substrate, C-O-Mn bonds are formed, promoting a tight connection between the composite materials. The assembled symmetric flexible supercapacitor (FSC) demonstrates impressive performance, with an areal specific capacitance of 934 mF/cm2, an energy density of 43.10 Wh/kg, a power density of 166.67 W/kg and a long cycle life (85 % Capacitance retention after 10,000 cycles), suggesting that they hold promise for FSC applications. [Display omitted] [ABSTRACT FROM AUTHOR]

SnS is an ideal material for supercapacitors because of its unique layered structure and excellent electrochemical performance, but the research of SnS based electrode materials of flexible self-supporting supercapacitors has been rarely exploited. In this study, microsphere like Co doped SnS grown on carbon nanofibers (Co-SnS@CNF) was prepared by electrospinning, hydrothermal method and annealing treatment. Co-SnS@CNF has great flexibility, high specific capacitance, excellent rate performance and cycle stability. Specifically, the specific capacitance is 750 F g−1 at the current density of 1 A g−1. The special microsphere structure with more electrochemical active sites and lower resistance of ion and charge transfer by Co doping are responsible for the superior electrochemical performances. Furthermore, when assembled Co-SnS@CNF as the symmetrical supercapacitor device, the energy density of 20.89 Wh Kg−1 and the power density of 376 W Kg−1 are achieved at the current density of 1 A g−1, while showing ultra-high cycle stability. Therefore, the Co-SnS@CNF offers excellent application potential for flexible self-supporting supercapacitors. • Revealing reasons for the high-performance of the microspherical Co-doped SnS. • The specific capacitance is 750 F g−1 at the current density of 1 A g−1. • The assembled symmetrical device exhibits the ultra-high cycle stability. [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]

The dramatic development of wearable electronics has led to extensive research into flexible supercapacitors as wearable energy storage devices. The practical application of supercapacitors to wearable electronics requires improved temperature tolerance and high energy density. Herein, we report the fabrication of a high-voltage flexible aqueous supercapacitor featuring high energy density and a wide operating temperature range. This is achieved by the strategy of simultaneously utilizing asymmetric electrodes and water-in-salt gel electrolyte (WISGE). Using NaClO 4 -based WISGE and asymmetric electrodes consisting of Na-inserted MnO 2 and N-doped carbon nanofibers, we obtain excellent electrochemical performance, including a gravimetric capacitance of 97.2 F g−1, energy density of 90 Wh kg−1, power density of 28.1 kW kg−1, operation voltage window of 2.6 V, and capacitance retention of 85.2% over 10,000 charge/discharge cycles. The fabricated flexible supercapacitor is stable under repeated temperature changes between − 20 and 80 °C, regardless of bending deformation. After three cycles of cooling and heating, the initial capacitance at room temperature is 95.1% recovered. This study demonstrates the potential application of our high-performance flexible aqueous supercapacitors to wearable devices, given their resistance to changes in environmental temperature and mechanical deformation. [Display omitted] • Supercapacitor consists of the asymmetric electrode and water-in-salt gel electrolyte. • Supercapacitor exhibits wide voltage window (2.6 V) and temperature range (−20 to 80 ℃). • The initial performance was maintained even after repeated temperature changes. • Performance is stable under repeated bending deformation over wide temperature ranges. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mn-doped PAN nanofibers were decorated with ZIF-67. • Oriented attachment of PVP/ZIF-67 occurred on Mn-doped PAN-2MI nanofibers. • PVP/ZIF-67/Mn-fibers carbonized at 900 ℃ resulted in flexible C/Co-CoO x /Mn-CNF. • The areal capacitance of 1263 mF·cm−2 was obtained at a current density of 0.25 mA·cm−2. • The energy density of 0.18 mWh·cm−2 was obtained at a power density of 0.5 mW·cm−2. Electrodes for flexible supercapacitors were fabricated from manganese-doped carbon nanofibers (Mn-CNF) decorated with carbon-coated Co-CoO x (C/Co-CoO x) nanotubes. The Mn-doped polyacrylonitrile (PAN)–2-methylimidazole (2MI) solution was electrospun using optimized Mn concentrations and ZIF-67 was then surface loaded by wet impregnation with added polyvinylpyrrolidone (PVP). These ZIF-67 loaded Mn-fibers, when annealed, resulted in carbon-coated C/Co-CoO x nanotubes on the Mn-CNF surface. In the presence of PVP, ZIF-67 oriented attachment occurs, forming evenly dispersed CoO x particles even after high temperature annealing. XRD spectra exhibit the formation of metallic Co nanoparticles (NPs), whereas Raman spectra and XPS indicate Co particle oxidation. A carbon coating limits the oxidation of Co; thus, the particles are called C/Co-CoO x. A symmetric supercapacitor cell prepared using the CNFs decorated with C/Co-CoO x using an aqueous electrolyte has a capacitance of 1263 mF⋅cm−2 at a current density of 0.25 mA⋅cm−2 and a wide potential window of 1.4 V for the optimal case. Long-term cycling showed 110 % capacitance retention after 10,000 cycles. Moreover, bending tests and powering LEDs demonstrated the flexibility and improved charge storage of the prepared nanofiber electrodes. [ABSTRACT FROM AUTHOR]