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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]

Summary: The development of efficient methods to achieve a porous activated carbon nanostructures electrode for high‐performance electrochemical double‐layer capacitor (EDLC) is urgently needed at present. In this study, biomass‐based porous hollow carbon nanofiber/nanosheet with suitable micro/mesopores was successfully prepared using a low‐cost simple approach through chemical activation at direct pyrolysis. Biomass‐based porous carbon was performed in two different chemical activation of KOH and ZnCl2. The effects of the different KOH/ZnCl2 concentrations at high‐temperature pyrolysis on the morphological structure and porosity were investigated. The synthesized activated carbon possesses micro/mesopores hollow nanofiber/nanosheet, which enhanced specific surface area from 15.163 m2 g−1 to ultrahigh specific surface area of 1041.900 m2 g−1. These behaviors exhibit a high specific capacitance of 213 F g−1 in a two‐electrode system with excellent energy and power density of 29.6 Wh kg−1 and 106.6 W kg−1 at 1 M H2SO4 aqueous electrolyte. These results provided accurate information about a feasible approach to synthesize biomass‐based porous hollow carbon nanofiber/nanosheet to boost high‐performance energy storage devices. [ABSTRACT FROM AUTHOR]

Summary: The design of inexpensive, binder‐free electrodes with high energy densities from naturally occurring compounds poses an interesting challenge for the construction of high‐performance supercapacitors. In particular, the synthesis of highly conductive carbon electrodes starting from miscanthus‐derived (silver grass) lignin with inorganic active sites is of interest for hybrid supercapacitors. In this work, Ni‐Mn sulfide nanograin networks are embedded on lignin‐derived carbon nanofibers (LCNFs) by electrospinning, followed by either direct vapor‐phase sulfidation or peroxidation‐induced sulfidation in an inert atmosphere. After either of the two different sulfidation processes, the direct transformation of Ni‐Mn sulfide on carbon nanofibers results in highly mechanically flexible freestanding electrodes, with a good specific capacity of 652.3 C g−1 at 1 A g−1, excellent current rate properties (73.6% capacity retention at 20 times the initial current density), and a cycling stability of 91.3% after 5000 cycles, even at the high current density of 10 A g−1. These outstanding properties are attributed to the rational design of surface‐embedded Ni‐Mn sulfide nanograins on the 3D LCNFs and the fascinating synergetic and graphitic nature of the fibrous web, which increases conductivity, influences the interfacial contact, and promotes highly electrochemically active sites on the electrode surface. Furthermore, an aqueous hybrid supercapacitor assembly of LCNFs‐NiMnS//activated carbon (AC) is demonstrated, with a maximum energy density of 52.4 W h kg−1 at a power density of 800 W kg−1, as well as 92.3% capacitance retention even after 10 000 cycles. This work not only establishes a high‐capacity anode but also provides an ideal strategy for designing flexible and conductive heterostructure network for various energy storage applications. [ABSTRACT FROM AUTHOR]

Summary: A hybrid nanostructure with partially reduced graphene oxide (rGO) and carbon nanofibers (CNFs) was fabricated and used as supercapacitor electrodes. A straightforward, environmentally friendly, and low‐cost microwave‐assisted reduction process was developed for the synthesis of rGO/CNF hybrid structures. The fabricated supercapacitor devices showed a specific capacitance of 95.3 F g−1 and a superior long‐term cycling stability. A capacitance retention of more than 97% after 11 000 galvanostatic charge discharge cycles was obtained. These and other results reported in this paper indicate that high‐rate, all‐carbon, rGO/CNF hybrid nanostructures are highly promising supercapacitor electrode materials. [ABSTRACT FROM AUTHOR]

Carbon nanomaterials such as carbon nanotubes, carbon nanofibers, and graphene are exploited extensively due to their unique electrical, mechanical, and thermal properties and recently investigated for energy storage application (supercapacitor) due to additional high specific surface area and chemical inertness properties. The supercapacitor is an energy storage device which, in addition to long cycle life (one million), can give energy density higher than parallel plate capacitor and power density higher than battery. In this paper, carbon nanomaterials and their composites are reviewed for prospective use as electrodes for supercapacitor. Moreover, different physical and chemical treatments on these nanomaterials which can potentially enhance the capacitance are also reviewed. [ABSTRACT FROM AUTHOR]

We report the fabrication and electrochemical performance of a flexible thin film supercapacitor with a novel nanostructured composite electrode. The electrode was prepared by in situ coprecipitation of two-dimensional (2D) MnO2 nanosheets at room temperature in the presence of carbon nanofibers (CNFs). The highest specific capacitance of 142 F/g was achieved for CNFs-MnO2 electrodes in sandwiched assembly with PVA-H4SiW12O40·nH2O polyelectrolyte separator. [ABSTRACT FROM AUTHOR]