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The combination of multiple electrode materials and their reasonable structural design are conducive to the preparation of composite electrodes with excellent performance. In this study, based on carbon nanofibers grown with Ni(OH)2 and NiO (CHO) prepared by electrospinning, hydrothermal growth, and low-temperature carbonization, five transition metal sulfides (MnS, CoS, FeS, CuS, and NiS) were hydrothermally grown on their surfaces, exhibiting that CHO/NiS had the optimal electrochemical properties. Subsequently, the effect of hydrothermal growth time on CHO/NiS revealed that the electrochemical performance of CHO/NiS-3h was optimal, with a specific capacitance of up to 1717 F g−1 (1 A g−1), due to its multistage core–shell structure. Moreover, the diffusion-controlled process of CHO/NiS-3h dominated its charge energy storage mechanism. Finally, the asymmetric supercapacitor assembled with CHO/NiS-3h as the positive electrode demonstrated an energy density of 27.76 Wh kg−1 at a maximum power density of 4000 W kg−1, and it still maintained a power density of 800 W kg−1 at a maximum energy density of 37.97 Wh kg−1, exhibiting the potential application of multistage core–shell composite materials in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

• 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]

Zinc-ion hybrid supercapacitors are garnering widespread interest in wearable energy storage devices due to their high power density, intrinsic safety and cost-effectiveness. However, the primary obstacle to their progress lies in the scarcity of cathode materials that concurrently demonstrate excellent flexibility and high energy density. Herein, we deliberately design a coaxial electrospinning ZIF-8 derived hollow carbon nanofiber film electrode (C-PAN(ZIF-8)@PVP) to achieve high-performance flexible ZHSCs. The distinctive configuration of C-PAN(ZIF-8)@PVP electrode comprises a shell of homogeneously distributed ZIF-8 derived porous carbon nanoparticles, which are bound together by N-doped carbon fibers derived from polyacrylonitrile (PAN), and a channel through the fiber created by the decomposition of polyvinylpyrrolidone (PVP). This unique architecture coupled with N, O co-doping bestows ample electrolyte infiltration, complete exposure of active sites, and a rapid pathway for electron conduction, resulting in facilitated ion diffusion kinetics, abundant active sites and enhanced electronic conductivity of the C-PAN(ZIF-8)@PVP electrode. As a result, the assembled ZHSC delivers a high reversible capacity of 116 mAh g−1 at 0.1 A g−1 and remarkable capacity retention of 100% over 4000 cycles at 5 A g−1. Moreover, it exhibits exceptional mechanical flexibility, capable of delivering stable output under arbitrary deformation. The intricate structural design strategy offers valuable insights for the development of high-performance electrode materials. Low reversible capacity and poor mechanical flexibility are the major obstacles that restrict the application of zinc-ion hybrid capacitors in wearable energy storage. We report a coaxial electrospinning strategy to construct C-PAN(ZIF-8)@PVP cathode which delivers a high reversible capacity of 116 mAh g−1 at 0.1 A g−1, offering profound insights in the realm of wearable electronic devices. [Display omitted] • Non-aggregated ZIF-8 derived hollow carbon nanofiber electrode is deliberately designed via co-axial electrospinning process. • Hollow architecture with N, O co-doping enhances electrolyte infiltration, active sites exposure, and electron conduction. • The distinctive electrode exhibits exceptional mechanical flexibility and remarkable capacity retention. [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]

In this paper, we proposed the synthesis of CoFe nanoparticles (NPs) which have been deposited on carbon nanofibers (CNFs) with a facile electrospinning route followed by thermal reduction. The performance of obtained CNF supercapacitors are improved from 51 to 190 F/g (247 mF/cm2) at 0.5 A/g with the combination of CoFe NPs and graphitized carbon layers The device possessed an energy and power density of 6.6 Wh/kg and 125 W/kg, respectively. Furthermore, the capacitance retention can still maintain about 96.6% after 10,000 cycle test and it is worth noting that the cycling stability is ultrahigh. This research proves that bimetallic nanoparticles embedded in CNFs can elucidate new insights into the development new nanofiber electrode materials for the next generation of symmetric supercapacitors. [ABSTRACT FROM AUTHOR]

There is a growing interest to hybrid energy storage devices, such as lithium-ion capacitors, in which battery-type electrodes are combined with capacitor-type ones. It is anticipated that the energy density (either gravimetric or volumetric) of lithium-ion capacitors is improved if pseudocapacitive or fast insertion materials are used instead of conventional activated carbon (AC) in the capacitor-type electrode. MXenes, a new family of two-dimensional transition metal carbides, demonstrate metallic conductivity and fast charge-discharge behavior that make them suitable for this application. In this study, we move beyond single electrodes, half-cell studies and demonstrate three types of hybrid cells using Nb 2 CT x –carbon nanotube (CNT) films. It is shown that lithiated graphite/Nb 2 CT x -CNT, Nb 2 CT x -CNT/LiFePO 4 and lithiated Nb 2 CT x -CNT/Nb 2 CT x -CNT cells are all able to operate within 3 V voltage windows and deliver capacities of 43, 24 and 36 mAh/g (per total weight of two electrodes), respectively. Moreover, the polarity of the electrodes can be reversed in the symmetric Nb 2 CT x -CNT cells from providing a positive potential between 0 and 3 V to a negative one from −3 to 0 V. It is shown that the volumetric energy density (50–70 Wh/L) of our first-generation devices with MXene electrodes exceeds that of a lithium titanate/AC capacitor. [ABSTRACT FROM AUTHOR]

• N-doped porous carbon nanofibers are synthesized via a simple hydrothermal method. • Carbon nanofibers are derived from their phenolic-resin-based analogues. • The mechanism underlying is proposed in the viewpoint of micelle evolvement. • N-doped carbon as electrode material offers superior electrochemical performance. Carbon nanofibers (CNFs), possessing high electrical conductance and facilitating fast electron transfer due to 1D structure, attract more research interests in the field of energy storage/conversion. It is highly desirable to develop a simple synthetic approach to prepare high quality CNFs for high efficient electrode material. Herein, a facile method is developed to prepare nitrogen-doped porous CNFs with high aspect ratio by direct pyrolysis of phenolic-resin-based precursors which are synthesized via a simple hydrothermal approach. After activation by KOH, the nitrogen-doped porous CNFs demonstrate a high surface area up to 1814.1 m2/g thereby offering a high capacitance while working as the electrode material assembled in a supercapacitor. The activated CNFs as electrode material present a high specific capacitance of 333.5F g−1 at a current density of 0.5 A g−1 in a three-electrode cell. After 10,000 cycles of charge–discharge tests at 5A g−1, the decay in specific capacitance is only 3.7 %, indicating a high reversibility. Also, the tests in a two electrode system show a high energy density of 8.6 Wh kg−1 at a power density of 25 W kg−1. Therefore, the nitrogen-doped CNFs derived from its phenolic-resin-based precursor hold a promise for an efficient electrode material in supercapacitor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel NPR structure for electrospun carbon-based electrode by LDW were obtained. • All-in-one AMSC was assembled from versatile nanofiber as electrode and separator. • The solid-state AMSC showed excellent mechanical and electrochemical properties. It is very necessary to design electrodes with satisfactory electrochemical performance and robust mechanical properties for flexible energy storage devices. Herein, a self-supporting electrode with Negative Poisson's Ratio (NPR) structure was fabricated by combining electrospinning and laser direct writing technology, which overcame the limitation that the traditional carbon-based materials cannot be stretched and avoided the integration problem of rigid electrodes and soft substrates in the conventional stretchable devices. Furthermore, a quasi-solid-state asymmetric micro-supercapacitor with NPR structure was assembled by an as-spun separator coated with gel electrolyte and two composite electrodes composed of carbon nanofibers and nanoarrays (CNF@Fe 2 O 3 nanorods and CNF@MnO 2 nanosheets). The apparatus not only reached an extended voltage window of 2 V, but also achieved an area energy density of 26 μWh·cm−2 at a power density of 0.55 mW·cm−2, which was superior to other wearable micro-supercapacitors. [ABSTRACT FROM AUTHOR]

Highly porous carbon electrodes for supercapacitors with high energy storage performance were prepared by using a new precursor blend of aromatic polyimide (PI) and polyvinylidene fluoride (PVDF). Supercapacitor electrodes were prepared through the electrospinning and thermal treatment of the precursor blends of aromatic PI and PVDF. Microstructures of the carbonized PI/PVDF nanofibers were studied using Raman spectroscopy. Nitrogen adsorption/desorption measurements confirmed their high surface area and porosity, which is critical for supercapacitor performance. Energy storage performance was investigated and carbonized PI/PVDF showed a high specific capacitance of 283 F/g at 10 mV/s (37% higher than that of PI) and an energy density of 11.3 Wh/kg at 0.5 A/g (27% higher than that of PI) with high cycling stability. [ABSTRACT FROM AUTHOR]

Porous carbon nanofibers (CNFs) with high energy storage performance were fabricated with a single precursor polymer, 6FDA-TFMB, without the use of any pore-generating materials. 6FDA-TFMB was synthesized, electrospun, and thermally treated to produce binder-free CNF electrodes for electrochemical double-layer capacitors (EDLCs). Highly porous CNFs with a surface area of 2213 m2 g−1 were prepared by steam-activation. CNFs derived from 6FDA-TFMB showed rectangular cyclic voltammograms with a specific capacitance of 292.3 F g−1 at 10 mV s−1. It was also seen that CNFs exhibit a maximum energy density of 13.1 Wh kg−1 at 0.5 A g−1 and power density of 1.7 kW kg−1 at 5 A g−1, which is significantly higher than those from the common precursor polymer, polyacrylonitrile (PAN). [ABSTRACT FROM AUTHOR]

Tailoring the chemical structures of a precursor polymer for carbon nanofibers (CNFs) produced by thermal treatment of electrospun nanofibers was studied to prepare the electrodes for electrochemical double layer capacitors (EDLCs). To improve energy storage performance of CNF electrodes, 6FDA-durene nanofibers were crosslinked by a vapor crosslinking method, and subsequently carbonized. Chemical modification via crosslinking was confirmed by FTIR spectra while the conversion of crosslinked 6FDA-durene into carbon was done by Raman spectroscopy. Electrochemical performance of these CNF electrodes was evaluated by assembling coin cells, and the CNFs derived from crosslinked 6FDA-durene nanofibers showed higher specific capacitances, energy densities and cycling stability than those from non-crosslinked ones. It was also shown that CNFs prepared using 1 min crosslinking exhibit the highest energy storage performances, a specific capacitance of 301 F g−1 (at 10 mV s−1), and the maximum energy density of 11.1 Wh kg−1 (at 0.5 A g−1) and power density of 1.8 kW kg−1 (at 6 A g−1). Surface area and porosity of CNFs, which is critical for the performance of EDLC electrodes, were studied by nitrogen adsorption/desorption measurements, and it was clearly seen that surface crosslinking of precursor polymers improved surface properties of the resultant CNFs. [ABSTRACT FROM AUTHOR]

Lignin was blended with polyacrylonitrile (PAN) in different ratios and fabricated into carbon nanofiber electrodes by electrospinning followed by thermal stabilization, carbonization and subsequent activation by CO2 of the carbonized mats. These carbon fiber electrodes exhibit high surface area, high mesoporosity, high graphitic content and high electrical conductivity. Activated carbon nanofiber mats derived from PAN:Lignin 70:30 blends display a surface area of 2370 m2 g−1 with 0.635 cm3 g−1 mesopore volume. These results are due to the selective partial removal of carbonized lignin during the activation step. Coin cell supercapacitors employing these electrodes exhibit 128 Fg−1 specific capacitance, 59 Wh kg−1 energy density and a 15 kW kg−1 power density when operated at 3.5 V using an ionic liquid electrolyte. Since lignin is an inexpensive, abundant, and green polymer, incorporating it into carbon blends enhances the scalability of such materials in energy storage applications. [ABSTRACT FROM AUTHOR]