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The hydroxyl-functionalized poly (amic acid) (PAA) is first synthesized from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and electrospun into nanofibers. Then, the PAA nanofibers are thermally imidized at 300 °C and rearranged at 450 °C, followed by an ultimate carbonization to obtain hydroxyl-functionalized polyimide (HPI) based carbon nanofibers (CNFs). When the PAA concentration and carbonization temperature are respectively optimized as 28 % and 800 °C, the obtained CNF specimen HPI(6FAP-6FDA)-28-800 exhibits a better electrochemical performance, with a specific capacitance of 226.3 F g−1 at 0.5 A g−1. Subsequently, the HPI(6FAP-6FDA)-28-800 is subjected to KOH activation treatment. When the CNF/KOH mass ratio is 1/3, the activated sample CNF(6FAP-6FDA)-1/3 displays a maximum specific capacitance of 354.0 F g−1, coupled with a high rate-performance of 75 % (10 A g−1). Furthermore, a button-type supercapacitor (SC) assembled by two pieces of self-supporting CNF(6FAP-6FDA)-1/3 membrane attains an energy density maximum of 11.39 W h kg−1 at a power density of 250 W kg−1. Under 10,000 cycles of charging-discharging, the SC demonstrates an outstanding working stability. In brief, this study reports a novel polymer precursor for the preparation of N, O co-doped active CNFs, and provides an insight into the relationship between the chemical structure, microstructure and electrochemical performance for self-supporting SC electrodes. • The N, O co-doped activated carbon nanofibers were prepared. • The o -hydroxyl polyimides containing rich –C(CF 3) 2 - structures were used as precursors. • The self-supporting electrodes exhibited superior capacitive performances. [ABSTRACT FROM AUTHOR]

Using renewable biomass precursors to develop high-performance carbon electrodes is a promising approach for the advancement of supercapacitors. This work proposes a feasible strategy to prepare self-supporting flexible porous carbon nanofibers by electrospinning and carbonizing the mixture of cuttlefish ink, polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA). The impacts of cuttlefish ink precursor on the structure, elemental composition, and capacitance properties of carbon nanofibers have been studied. Herein, the unique structural advantage of cuttlefish ink can significantly optimize the porous structure of carbon nanofibers. Due to the hierarchical porous structure, large specific surface area, hollow channels and high nitrogen content, the carbon nanofibers offer a high specific capacitance of 364.8 F g−1 at 0.5 A g−1 current density, alongside desirable rate performance and cycle life. Furthermore, the carbon nanofiber electrode performs good mechanical flexibility. The flexible solid-state supercapacitor based on this electrode exhibits 14.1 Wh kg−1 energy density at 0.4 kW kg−1 power density, and 97.8% capacitance retention after 5000 cycles. The favorable capacitive properties make this carbon nanofiber material a potential candidate for supercapacitor electrodes. [Display omitted] • Electrospun porous carbon nanofibers (CPP–CNF) were prepared from cuttlefish ink. • CPP-CNF features hierarchical pores and hollow channels. • CPP-CNF is mechanically flexible with superior capacitive performance. • The flexible supercapacitor achieves high energy density and cycling stability. [ABSTRACT FROM AUTHOR]

Although high-rate, long-cycle energy storage devices play a crucial role in the field of energy storage, they are relatively under-reported. This work reports the preparation of fibrous porous carbons ultra-high specific surface area of 3384 m2g-1 derived from medical waste degreased cotto. As electrode material for supercapacitors, the resulted porous carbons demonstrate an ultra-high specific capacitance of 505.5 F g−1 at 0.5 A g−1 in a three-electrode system with 6 M KOH as electrolyte. Assembled symmetric supercapacitors show a specific capacitance of 403.84 F g−1 at 0.5 A g−1 and 294.95 F g−1 at 20 A g−1, with a capacity retention rate of 73.62 %, impressively retaining 82.66 % of the capacity after 300000 cycles at 10 A g−1. The average capacity loss is minimal, at 0.000557 % per cycle. The as-assembled zinc-ion hybrid capacitors (ZIHCs) demonstrate a high energy density of 69.33 Wh kg−1 at 2400 W kg−1 in 2 M ZnSO 4 electrolyte and retain 99.3 % capacity after 120000 cycles at 7 A g−1, suggesting the excellent long cycling stability. These outstanding performances demonstrate a promising solution for recycling and utilizing medical waste-degreased cotton in energy storage devices, also addressing the research gap in high-rate, long-cycle applications. • Medical decreased waste cotton is efficiently transformed into porous carbons. • Porous carbons exhibit an ultra-high specific surface area of 3384 m2g-1. • As For supercapacitors (SCs), it exhibits high capacitance of 505.5 F g−1. • After 300000 cycles, SCs maintain a high-capacity retention rate of 82.66 %. • After 120000 cycles, the ZIHCs maintain a high-capacity retention rate of 99.3 %. [ABSTRACT FROM AUTHOR]

Herein, a kind of hydroxyl and sulfonyl-containing diamine 2,2-bis[4-(3-hydroxy-4-aminophenoxy)phenyl]sulfone (BHAPS) was first synthesized and polymerized with pyromellitic dianhydride (PMDA) to obtain poly(amic acid) (PAA) solution. Then, the PAA nanofibers were fabricated by electrospinning technology, which were further thermally treated at 300 °C for imidization, 450 °C for rearrangement and a certain final temperature for carbonization to obtain carbon nanofibers (CNFs). The PAA concentration, carbonization temperature and thermal rearrangement time were separately optimized, and the HPI-CNF-20-2-800 exhibited better electrochemical properties. Next, the HPI-CNF-20-2-800 was chemically activated with KOH to enhance specific surface area. The preferred A-HPI–CNF–1/3 demonstrated a specific capacitance maximum of 335.0 F g−1 at 0.5 A g−1, with a 73 % capacitance retention at 10 A g−1. Furthermore , the SC device was symmetrically assembled with self-supporting A-HPI–CNF–1/3 membranes, which showed a maximum energy density of 10.42 Wh kg−1 at a power density of 250.0 W kg−1. In addition, the capacitance retention rate of the SC reached 99.94 % even after 50,000 charge/discharge cycles at a current density of 1 A g−1. Thus, this work reports a new precursor to prepare N, O, S co-doped active CNFs with better electrochemical performance, which will provide a reference for the preparation of co-doped self-supporting SC electrodes. • A new kind of diamine monomer containing hydroxyl and sulfonyl was synthesized. • The N, O, S co-doped activated carbon nanofibers were prepared. • The capacitive performance of self-supporting electrode was effectively boosted. [ABSTRACT FROM AUTHOR]

In this work, the carbon nanofibers (CNFs) are first prepared by electrospinning the poly(amic acid) (PAA) solution containing aryl imidazole and hydroxyl groups, followed by thermal imidization, rearrangement and carbonization. Then, the CNFs are further treated with KOH to obtain activated CNFs. The effects of the PAA concentration, rearrangement time, carbonation temperature and mass ratio of CNFs/KOH on the electrochemical properties are investigated. The results show that the sample HPI-CNF-20-2-800 displays the best electrochemical performance. After activation, the A-HPI–CNF–1/3 exhibits a maximum specific surface area of 1762 m2 g−1 and pore volume of 0.92 cm3 g−1, leading to a high specific capacitance of 325.0 F g−1 at 0.5 A g−1. Moreover, the specific capacitance can reach 234.6 F g−1 when the current density is 20 A g−1. Furthermore, the symmetric supercapacitor fabricated by A-HPI–CNF–1/3 shows a maximum energy density of 29.17 Wh kg−1, coupled with a power density of 500.0 W kg−1. The capacitance retention rate of the supercapacitor maintains about 99.95% after 20,000 charge-discharge cycles at 1 A g−1. Therefore, this work provides a novel rearrangeable precursor for the preparation of activated CNFs with a considerable electrochemical performance, which will be considered as excellent electrode materials for supercapacitors. [Display omitted] • A novel polyimide precursor with aryl imidazole and hydroxyl groups was synthesized. • The CNFs contained abundant N and O atoms and high specific surface areas. • The supercapacitor with activated CNFs showed a high energy density of 29.17 Wh kg−1. [ABSTRACT FROM AUTHOR]

Carbon nanofibers modified with carboxyl groups (CNF-COOH) possessing good wettability and high porosity are homogeneously deposited with amorphous manganese dioxide (amorphous MnO 2 ) by potentiodynamic deposition for asymmetric super-capacitors (ASCs). The potential-cycling in 1 M H 2 SO 4 successfully enhances the hydrophilicity of carbonized polymer nanofibers and facilitates the access of electrolytes within the CNF-COOH matrix. This modification favors the deposition of amorphous MnO 2 and improves its electrochemical utilization. In this composite, MnO 2 homogeneously dispersed onto CNF-COOH provides desirable pseudocapacitance and the CNF-COOH network works as the electron conductor. The composite of CNF-COOH@MnO 2 -20 shows a high specific capacitance of 415 F g −1 at 5 mV s −1 . The capacitance retention of this composite is 94% in a 10,000-cycle test. An ASC cell consisting of this composite and activated carbon as positive and negative electrodes can be reversibly charged/discharged to a cell voltage of 2.0 V in 1 M Na 2 SO 4 and 4 mM NaHCO 3 with specific energy and power of 36.7 Wh kg −1 and 354.9 W kg −1 , respectively. This ASC also shows excellent cell capacitance retention (8% decay) in the 2V, 10,000-cycle stability test, revealing superior performance. [ABSTRACT FROM AUTHOR]

In this article, vanadium nitride quantum dot/nitrogen-doped microporous carbon nanofibers (VNQD/CNF) is developed by a method of combination of electrostatic spinning and high-temperature calcination under the atmosphere of NH 3 : N 2 = 3: 2 for high performance supercapacitors. VNQD dispersing into CNF, enrichment of N atom doped in carbon bulk, and abundant porous structure not only prevent the growth and aggregation of VN nanoparticles, improve electrical conductivity, wettability, and stability of the electrode materials, but also enhance fast migration of electrolyte ions during the electrochemical process. Thus, VNQD/CNF exhibits a high specific capacitance of 406.5 F g −1 at 0.5 A g −1 and a good rate capability with a capacitance retention of 75.1% at 5.0 A g −1 . Additionally, VNQD/CNF as a negative electrode are combined with Ni(OH) 2 as a positive electrode to fabricate the hybrid supercapacitor of VNQD/CNF//Ni(OH) 2 . Remarkably, at a power density of 774.6 W kg −1 , the supercapacitor device delivers an ultrahigh energy density of 31.2 Wh kg −1 . [ABSTRACT FROM AUTHOR]

Helical carbon nanofibers (HCNFs) assembly structure possesses huge development prospects in sorts of applications. Here we report a facile yet versatile strategy for synthetic HCNFs assembly structures (Sn-HCNFs) from Sn-based metal-organic framework (Sn-MOF) via an ethanol flame method (EFM) in atmospheric environment. As Sn-MOF is burned in ethanol flame, HCNFs grow on the surface of Sn-MOF progressively, forming an assembly structure with SnO 2 core and HCNFs-forest shell. The process of Sn-HCNFs formation is also investigated by a series of experiments, which demonstrate that, in ethanol flame, Sn-MOF is first converted to SnO 2 , and then SnO 2 catalyzes the formation of Sn-HCNFs. Furthermore, our strategy can also be extended to the preparation of various MOFs-based HCNFs and carbon nanotubes (CNTs)/carbon nanofibers (CNFs) assembly architectures. By electrochemical tests, Sn-HCNFs as electrode materials in supercapacitors exhibit superior electrochemical performances than pure HCNFs. The supercapacitors with the Sn-HCNFs electrode can remain the energy density of 21.67 Wh kg−1 at a very high-power density of 5000 W kg−1. Our strategy provides an alternative route to acquire various HCNFs or CNTs/CNFs assembly structures conveniently and will stimulate further researches on preparation and applications of them. [Display omitted] • HCNFs assembly structure (HCAS) grows from Sn-MOF in ethanol flame facilely. • SnO 2 derived from Sn-MOF in ethanol flame acts as the catalyzer for HCAS growth. • HCAS has more excellent electrochemical performance than HCNFs in supercapacitors. • Various CNFs/CNTs assembly structures form from different MOFs in ethanol flame. [ABSTRACT FROM AUTHOR]

Recently, a new class of mixed polyanionic compounds with general formula Na 3 MPO 4 CO 3 (M = Ni, Mn, Fe, Co, Cu), discovered through high-throughput computations have attracted much attention for its secondary battery applications and safety aspects. Here, we combine electrochemical measurements with inductively coupled plasma-optical emission spectrometer (ICP-OES), energy-dispersive X-ray (EDX), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and an ab-initio DFT approach to unravel the dynamic self-limiting surface restructuring of Na 3 NiCO 3 PO 4 in aqueous 1 M KOH/NaOH electrolyte. The etching of lattice CO 3 2-, PO 4 3- and Na serves as the key to trigger the surface reconstruction. This work establishes a fundamental understanding of the pseudocapacitance mechanism associated with surface self-reconstruction of mixed polyanionic compounds. The reconstruction-derived self-limiting dense Ni(OH) 2 layers at the surface and its oxidation to NiOOH at anodic potentials can be attributed to the observed high-performance pseudocapacitive behavior. The surface reconstructed Na 3 NiCO 3 PO 4 electrode exhibits high specific capacitance (2378.2 F g−1 at 1 A g−1). The assembled symmetric pseudocapacitor delivers a high energy density (57.2 Wh kg−1), power density (1500 W kg−1) at 1 Ag-1 and long cycle life (13000 cycles) with 100% retention. [Display omitted] • The pseudocapacitive behavior of the Na 3 NiCO 3 PO 4 is tested. • The Na 3 NiCO 3 PO 4 undergo surface self-reconstruction. • The etching of lattice CO 3 2-, PO 4 3- and Na lead to the formation of Ni(OH) 2 at the surface. • The electrode exhibits high specific capacitance 2378.2 F g−1 at 1 A g−1 • The assembled device delivers a high energy density, power density and long cycle life. [ABSTRACT FROM AUTHOR]

Carbon-based supercapacitors with outstanding electrochemical performances are strongly desired for the development of portable and wearable electronics. From the free radical engineering point of view, this study innovatively developed carbon/carbon gradient-structured microspheres (CCGMs) by the strategy of "third-order graduation polymerization" and "dynamic radical oxidation". Compared to conventional hybrid materials, for the first time, the gradient structure is proved to be extremely beneficial for improving the capacitive performance. Benefiting its gradient-structured advantages, the CCGMs exhibited "three-ultrahigh" performance with gravimetric, volumetric, and areal capacitances of 408.23 F g−1, 741.11 F cm−3, and 4390 μF cm−2, respectively. In addition, the assembled all-solids-state micro-supercapacitors delivered superior volumetric and areal specific capacitances (7.704 F cm−3 and 9.245 mF cm−2 at 5 μA cm−2), excellent life-span (100% after 12000 cycles), excellent volumetric and areal energy densities (1070 mWh cm−3 and 1284 μWh cm−2). This work paves a new way to develop unique carbon composites for high‐performance energy storage devices. • A third-order graduation polymerization method was developed. • The dynamic radical oxidation method was used for ultramicroporous-confined defects. • The gradient structure could improve the "three-ultrahigh" performance of carbons. [ABSTRACT FROM AUTHOR]

Achieving high specific surface area and ion accessibility in graphene-based electrodes with a high mass loading for supercapacitors poses a significant challenge because strong π-π stacking of graphene sheets often blocks the access of electrolyte ions to active sites. Herein, we report a novel protocol to prepare free-standing laminated graphene/carbon nanofiber films as high areal mass-loading electrodes through a layer-by-layer electrospinning technique. The unique laminated structure of graphene/carbon nanofiber thin films can enhance electrolyte penetration and increase transportations of ions/electrons. The symmetric supercapacitors (SCs) using the as-obtained graphene/carbon nanofiber films as electrodes reach areal specific capacitance of 1536 mF cm−2 at a current density of 1 mA cm−2. Most importantly, the areal energy density of the SCs can reach 0.22 mWh cm−2 at a power density of 1 mW cm−2 with a high areal mass loading of 24 mg cm−2. The exceptional electrochemical properties of the laminated graphene/carbon nanofiber films render them promising materials for electrodes in SCs. [Display omitted] • Laminated graphene/CNFs were prepared via layer-by-layer electrospinning. • The unique laminated structure enhances ions accessibility at high mass loading. • The assembled symmetric supercapacitor exhibits high areal specific capacitance. [ABSTRACT FROM AUTHOR]

Carbon nanofibers from electrospun polymer nanofibers have received considerable attention. However, most of the carbon nanofibers with a surface area above 1000 m2/g were reported to have a supercapacitor electrode capacitance far below 350 F g−1. Herein, we report a novel carbon nanofibrous material that has a supercapacitor electrode capacitance as high as 394 F g−1 (1.0 A g−1). We used a polymer blend of polyacrylonitrile (PAN) and novolac (NOC) as materials, to electrospin them into precursor nanofibers and subsequently carbonize the nanofibers into carbon nanofibers. The carbon nanofibers prepared had a specific surface area as high as 1468 m2 g−1 with a meso-micro pores (average pore size 2.2 nm) predominated porous structure. The carbon nanofiber electrodes after 10,000 cycles of charging and discharging at 1.0 A g−1 maintained the capacitance almost unchanged. At the optimal condition, the supercapacitor device made of the electrodes had an energy density as high as 13.6 Wh∙kg−1 (at 0.5 kW kg−1). The high capacitance value comes from the carbon nanofibers with a large surface area and a unique porous structure. The high inter-fiber interconnection contributes to high capacitance. This super-high surface area carbon may be useful for the development of high-performance supercapacitors and other energy devices. Image 1 • Carbon nanofibers are prepared from electrospun polyacrylonitrile/novolac. • They contain micro-mese pores with a surface area as high as 1468 m2 g−1. • Electrodes made from the carbon nanofibers show a capacitance of 394 F g−1. • High capacitance originates from the unique structure and large surface area. [ABSTRACT FROM AUTHOR]

Bimetallic carbides have aroused wide attention for energy-storage applications recently. In this work, one-dimensional Fe 2 MoC/CNFs (Fe 2 MoC/C nanofibers) are successfully synthesized via a facile electrospinning method for the first time. To obtain the most integrated structure between the Fe 2 MoC nanoparticles and carbon nanofibers, we explore the optimal heating rate during the carbonization treatment. Fe 2 MoC/CNFs exhibits an integrated one-dimensional structure under 800 °C with a heating rate of 5 °C/min. As revealed in the experimental results, Fe 2 MoC/CNFs possesses a high specific surface area of 196.9 m2/g, a high specific capacitance of 347.8 F/g at the current density of 1 A/g, an excellent rate capability of 91% capacitance retention from 1 A/g to 40 A/g, and shows superior cycling stability with the capacitance retention of about 85.6% and Coulombic efficiency of about 100% after 5000 cycles. An asymmetric supercapacitor coin-cell device using Fe 2 MoC/CNFs as the positive electrode displays an energy density of 14.5 Wh/kg at a power density of 300 W/kg and an outstanding cycling life of 93% retention after 5000 cycles. The impressive electrochemical performance indicates that the Fe 2 MoC/CNFs composite is a promising material for efficient supercapacitors. Image 1 • Fe 2 MoC nanofibers can be prepared via a facile electrospinning method. • Fe 2 MoC/CNFs-5 exhibits a superior rate capability and cycle stability. • ASC coin-cell device shows a promising energy and power density. [ABSTRACT FROM AUTHOR]

Persuing both high energy and power density in one supercapacitor at low cost is very challenging to date. Here, we report the fabrication of nitorgen and Sulphur co-doped graphene (GN) modified lignin/polyacrylonitrile (PAN)-based carbon nanofiber (ACNFs) from mainly the biomass of lignin following a process of electrospinning, carbonization and activation. GN is used as nitrogen/sulphur immobilization agent to successfully capture HCN, NH 3 and SO 2 released from lignin and PAN during carbonization, and thus the content of heteroatoms of N and S in ACNFs is increased. The resulting ACNF with 0.30 wt% GN content possesses the maximum specific surface area of 2439 m2 g−1. It shows a typical three-dimensional porous network structures with the highest heteroatom doping content and high degree of crystallinity. The assembled supercapacitor exhibits superior electrochemical performance with ultra-high specific capacitance of 267.32 F g−1, low equivalent series resistance of 5.67 Ω, and outstanding cycling stability of 96.7% capacitance retention after 5000 cycles of charge/discharge in a two-electrode system with 6 mol L−1 KOH as electrolyte. Most importantly, the assembled symmetric supercapacitor shows that ACNFs doping with GNs increases the energy density from 4.12 to 9.28 Wh kg−1 and at the same time with barely reduced power density. • Using GNs as an adsorbent to capture HCN, NH 3 , SO 2 released in carbonization. • Proposing the water wetting behaviour to evaluation the supercapacitor performance. • Elucidated the mechanism between heteroatom doping and electrochemical properties. [ABSTRACT FROM AUTHOR]