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• MnO 2 /CNF/Ag nanofabric electrodes are developed for flexible supercapacitors. • The brittle issue in the CNF electrode is greatly improved by an Ag incorporation. • The optimized MnO 2 /CNF/Ag electrode has a specific capacitance of 184 F/g at 1 A/g. • An energy density of 16.3 Wh/kg and a power density of 400 W/kg was achieved. • A capacitance retention rate of 87 % was demonstrated when subjected to bending. Flexible supercapacitors are gaining increasing popularity due to their potential in powering portable, wearable, and lightweight electronic devices. In this study, we have successfully developed a high-performance flexible electrode for quasi-solid-state supercapacitors by incorporating Ag into carbon nanofibers (CNF) through electrospinning, and growing MnO 2 as an active material on the electrode using an in-situ redox method. The Ag and MnO 2 co-decorated CNF electrode offers several advantages over conventional CNF electrodes, including an enlarged reaction area, higher charge storage capacity, and improved resistance to brittleness issues. Among all the quasi-solid-state supercapacitors tested, the MnO 2 -decorated electrode with an optimized Ag incorporation exhibited the highest specific capacitance of 184 F/g at a current density of 1 A/g, representing a remarkable 17-fold increase compared to the reference CNF electrode. Furthermore, the Ag and MnO 2 co-decorated electrode demonstrated an energy density of 16.3 Wh/kg and a power density of 400 W/kg at the same current density. Notably, the electrode exhibited excellent flexibility, with a capacitance retention rate of 87 % when subjected to bending with a curvature ranging from 5 to 1.25 cm. Our results suggest that the Ag and MnO 2 co-decorated CNF electrode holds great promise for flexible energy storage applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In most of the porous carbon based electrode materials reported to date, the pores were open and directly exposed to electrolyte, and the materials suffered from a huge stress during long-term cycle at a large current density. These would inevitably cause an irreversible damage to the material structure, resulting in a dramatic capacity fade. In this work, the metal oxides composite nanofibers are first fabricated using an electrospinning technique, and then an oxidative polymerization of dopamine and a subsequent calcination are conducted to form a protecting shell. The inner carbon nanofibers have been obtained after removing the metal oxides nanoparticles. Owing to the robust dense carbon shell and inner porous carbon framework as well as intrinsic nitrogen doping, the prepared nanofibers electrode delivers high capacitances of 328 F g −1 at 1 A g −1 and 160 F g −1 even at an extremely high current density of 100 A g −1 in a 6 M KOH aqueous solution. The electrode maintains 77% of the initial capacity after 5000 cycles at 5 A g −1 . The assembled symmetric supercapacitor exhibits a high capacitance of 97.9 F g −1 at 1 A g −1 and still maintains at 60 F g −1 even at a high current density of 50 A g −1 . 73% of the initial capacitance is remained after 5000 cycles at a current density of 10 A g −1 . The experimental results reveal that the inner porous carbon nanofibers may be a promising electrode material for high-rate supercapacitors. [ABSTRACT FROM AUTHOR]

Electrochemical capacitors (ECs) can provide ultra-long cycle life and ultra-fast energy delivery, characteristics which most battery technologies lack. Making composites out of carbon and pseudocapacitive materials is a popular strategy directed on narrowing the gap in energy density with regard to batteries. Usually, the incorporation of pseudocapacitive materials leads to a decrease in power performance compared to a pure carbon matrix, due to inferior electrical conductivity. This work, however, presents significant improvement in rate capability demonstrated by a composite electrode containing carbon nanofibers (NCNF) and manganese oxides (MnO 2). The NCNF/MnO 2 is prepared with a common method through the reaction with permanganate. The material has excellent performance metrics, especially a 78.2% rate capability (capacitance retention at 15 A g−1 relative to 0.5 A g−1), more than 10 times that for the NCNF carbon matrix. The exceptional enhancement can be explained by the development of micropores and surface area of NCNF, thus alleviating the "pore starvation" issue, and surface functional groups variation that enhances capacitive performance. This work highlights the importance of paying attention to the modification of carbon substrate when investigating carbon composite electrodes e.g. carbon/MnO 2 networks. • N-doped carbon nanofiber (NCNF) electrodes were derived from cellulose. • Compositing NCNF with MnO 2 led to surprising enhancement in rate capability. • 88.8 F g−1 capacitance was obtained at 15 A g−1 for the composite electrode. • Porosity and surface chemistry of NCNF were improved during compositing. [ABSTRACT FROM AUTHOR]