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[Display omitted] • Self-O-doped Alpinia galanga stem-based carbon nanofiber succesfully synthesis. • The hierarchical porous carbon exhibit high specific surface area of 1065.58 m2/g. • The porous carbon was performed in solid-free binder form. • In 2-electrode system, supercapacitor possessed specific capacitance of 226F g−1. In this study, activated carbon with hierarchical pores and a nanofiber structure doped with oxygen was prepared using a pure biomass-based sustainable strategy involving integrated chemical impregnation and pyrolysis. Alpinia galangal stem was chosen as it functions as fast conductive network with abundant electrochemical active sites for high-grade electrode materials. The optimal precursor exhibited self-doping of oxygen ranging from 6.15 to 15.69 % with 1065.58 m2/g, which contributed to the redox reaction of the electrode material. When tested in a 2-electrode system, the porous carbon nanofibers showed a high specific capacitance of 226F g−1 at 1 A g−1 in 1 M H 2 SO 4 electrolyte, producing an energy density of 9.3483 Wh kg−1 with a coulombic efficiency of 89.01 %. The results showed that oxygen-doped hierarchical porous carbon nanofibers produced from Alpinia galangal stem biomass and designed to be solid-free of binders are highly promising as high-quality electrode materials that can improve sustainable supercapacitor performance. [ABSTRACT FROM AUTHOR]

• A facile method was reported by us to sustainably obtain 3D and defective nanocarbon from waste RS residue. • The key role of bacterial played in the formation of RS residue with unque structure and composition was revealed. • The underlying pyrolysis mechanism of RS residue is explored. • The obtained bio-char was demonstrated as a promising candidate for supercapacitor. Defective carbon nanomaterials with three-dimensional (3D) structure are showing great potential for advanced electrochemical storage and conversion devices, but its application is restricted by the synthesis, which is usually involved with complicate and energy-intensive processes. Herein, pyrolysis of rice straw (RS) residue, of which is collected from the bacterial assisted hydrolysis, is proposed by us here, and the obtained bio-char is defective with 3D structure and rich in oxygen-containing functional groups. Compared to the pristine one, specific surface area of the representative RS carbon (RSC2) was increased from 428.8 to 1131.7 m2 g−1. The assembled supercapacitor with RSC2 showed a high specific capacitance of 331F g−1 at a charge–discharge current density of 0.5 A g−1, and a capacity retention of 97.6% was maintained at 5 A g−1 even after 10,000 cycles. [ABSTRACT FROM AUTHOR]

• Series of Cu x NiCo 2−x O 4 synthesized by Microwave hydrothermal method. • The average grain size is in the range of 30–55 nm. • Highest Specific capacitance, C sp = 250.66 Fg−1 is observed for x = 0.06 sample. • Highest E = 22.22 Whkg−1 and P = 757.80 Wkg−1 were observed for x = 0.06 sample. A series of NiCu x Co 2-x O 4 with x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10 samples were synthesized using microwave hydrothermal method (MH). The structural, microstructural, and spectroscopic characterizations were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). All the samples are in Cubic phase with space group Fd3m. The samples x ≥ 0.08 shows some impurity phases. The average grain size for all the samples is in the range of 30–55 nm. The specific capacitance (C sp) 250.66 Fg−1, energy density (E) 22.22 Whkg−1 and power density (P) 757.80 Wkg−1 was observed for x = 0.06 with a mass loading of 7 mgcm−2 and in 2 M aqueous KOH electrolyte solution at a current density of 1 Ag−1. Therefore, the Cu doping with x = 0.06 shows good redox activities and hence can be used in electric batteries and supercapacitors. [ABSTRACT FROM AUTHOR]

Highlights • BCNT/CNF composites were synthesized by a single step method. • BCNT/CNF-based supercapacitors exhibit very high specific capacitance. • BCNT/CNF-based supercapacitors deliver an energy density of 63.7 Wh kg−1. Abstract We describe the in situ synthesis of branched carbon nanotubes/carbon nanofibers (BCNT/CNF) nanocomposite by a simple chemical vapor deposition method. Electrochemical characterization indicated that the BCNT/CNF based supercapacitors carried a high value of specific capacitance up to 207 F g−1 at a charge/discharge rate of 1 A g−1, which is much higher than branched carbon nanotubes (BCNT) in H 2 SO 4 electrolyte. The supercapacitor showed a very good cycling stability of 95.6% after 5000 charge/discharge cycles at a very high current density of 20 A g−1, and high energy density of 63.7 Wh kg−1 in EMIBF 4 organic electrolyte. [ABSTRACT FROM AUTHOR]

Composite of two metal oxides, SnO 2 and TiO 2 , is synthesized as 3D nanoflowers in large quantities by electrospinning technique. They show superior energy storage properties and photocatalytic performance than their components or conventional electrospun 1D nanofibers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu 0.95 Co 2.05 O 4 /Metal/NF exhibited relatively excellent performance. • The performance of Cu 0.95 Co 2.05 O 4 /Au/NF is good due to the close lattice spacing. • The metal buffer layer can effectively reduce the transfer resistance. The method of forming Cu or Au buffer layer on nickel foam (NF) by magnetron sputtering technology to enhance the energy storage capacity of following prepared supercapacitor anode material of Cu X Co 3-X O 4 was carried out in this paper, and the feasibility of surface treatment to improve the performance of supercapacitors was discussed. The buffer layer of Cu or Au can attenuate the lattice mismatch between NF and Cu X Co 3-X O 4 , and thus greatly reducing the transfer resistance and improving the electrochemical performance of the electrode material. The effect of Au is more obvious than Cu. The transfer resistance could be decreased effectively from 1.213 Ω to 0.012 Ω after Au sputtered, and the specific capacity increased spontaneously from 442.1C/g to 744.5C/g at a current density of 1A/g. The asymmetric supercapacitor (ASC) based on the modified anode material can achieve an energy density of 51.04Wh/kg when the power density is about 800 W/kg, and 93.9 % capacity retention rate after 4000 cycles. [ABSTRACT FROM AUTHOR]

In this study, a pulse-mode electrochemical deposition technique was employed to deposit dense and homogeneous Ni nanoparticles on the three-dimensional graphene network (3DGN) as the catalysts for growing the vertical aligned one-dimensional carbon nanofibers (CNFs) to fabricate the full-carbon hybrid nanoarchitecture of CNFs/3DGN for the supercapacitors. When tested as electrode for a supercapacitor, the CNFs/3DGN hybrid nanoarchitecture demonstrated to possess a large surface area and showed an excellent specific capacitance of 59.28 F g −1 at a current density of 0.17 mA cm −2 , also displayed good cycle stability with capacitance retention of 93.9% after 10,000 cycles in 6 M KOH electrolyte. [ABSTRACT FROM AUTHOR]

An easy method for preparing porous carbon nanospheres is presented by using commercial spherical poly(vinylidene fluoride) (PVDF) as precursors. The PVDF nanospheres are simply converted to porous carbon nanospheres by a low temperature defluorination treatment with an organic alkali and followed high temperature carbonization. The as-prepared carbon exhibits monodispersed spherical morphology with size of ~170nm, porous structure with a surface area of 523m²g-1 and nitrogen-doped functionality, which affords a capacitance of 190Fg-1 with good rate capability in 6molL-1KOH. [ABSTRACT FROM AUTHOR]

• The 3D honeycomb-like carbons (3DHCs) constructed by interconnected carbon nanosheets were prepared. • The 3DHCs present high specific surface area and 3D honeycomb-like structures. • The 3DHCs display high capacitance, high energy density and excellent cycle stability. Herein, the 3D honeycomb-like carbons constructed by interconnected carbon nanosheets (3DHCs) were prepared by salt template strategy. The 3DHCs present high specific surface area, honeycomb-like structures and 3D interconnected sheet-like network. As a result, the 3DHC displays high gravimetric capacitance of 326.5F g−1 at 0.05 A g−1, excellent rate capability of 246.3F g−1 at 50 A g−1 and high energy density of 11.3 Wh kg−1 when used as electrode for supercapacitor. Impressively, the capacitance of 3DHC 850 -based supercapacitor only decays 0.2% after 15,000 cycles. This work offers a low-cost, environmental-friendly method for the design of electrode materials for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]