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[Display omitted] • A solvent-freely polymerizing catechol and paraformaldehyde method was developed. • The present method derived carbon owns high nitrogen functionalties of 21.7 atom%. • The derived carbon achieves high energy density of 34.5 Wh L−1@1370 W/L. Fabrication of nitrogen functionalized carbon with high nitrogen content (over 10 atom%) by a route with simplified and solvent-free procedures would be both economically and environmentally scalable. We demonstrate here a simple solvent-free route towards synthesizing porous carbon doped by nitrogen functionalties (21.7 atom%) involving solid state catalytic polymerization of catechol and paraformaldehyde with g -C 3 N 4 as catalyst. Upon high-temperature treatment, the vaporized catechol and paraformaldehyde would be in situ polymerized on the surface of g -C 3 N 4 forming the composite of g -C 3 N 4 @resin. During the following carbonization process, the resin was carbonized to carbon skeleton, while the g -C 3 N 4 would be decomposed in situ doping the carbon skeleton. In our design, the avoidance of solvents in the whole synthesis procedure and the usage of g -C 3 N 4 in the preparation not only reduces the waste production, but also introduces high nitrogen species (21.7 atom%). As electrode for supercapacitor, the resultant SFC based electrode achieves a large specific capacitance of 391F cm−3@1.0 A/g and high energy density of 34.5 Wh/L@1370 W/L, suggesting a potential as electrode for energy storage. And more, the developed method offers a promising and alternative route for the fabrication of new materials in manner of green and environmentally friendly. [ABSTRACT FROM AUTHOR]

In this paper, porous NiO nanoflake arrays@V 2 O 5 nanoparticles (PNFAs@VNPs) composite is fabricated on Ni foam through a facile hydrothermal process. The PNFAs@VNPs composite has an ordered array structure, a large active surface, and favorable physical stability. Based on the CV profile, the specific capacitance can achieve 950 F g−1 and remain stable at 95.8 % of the original value after 5000 loops. When the PNFAs@VNPs composite is assembled into a symmetric supercapacitor, the energy density can reach 67.0 W h kg−1 at a power density of 550 W kg−1. Even if the power density rises to 11,000 W kg−1, the energy density can still be held at 25.3 W h kg−1. The high supercapacitive property of the PNFAs@VNPs composite is owed to the synergic action of the PNFAs and VNPs. The PNFAs@VNPs composite with the advantages of battery-type and capacitive-type pseudocapacitances has higher charge transfer dynamics, making it a potential supercapacitive electrode material. [Display omitted] • Porous NiO nanoflake arrays (PNFAs) is successfully prepared on nickel foam. • V 2 O 5 nanoparticles (VNPs) are loaded on the PNFAs to form a hierarchical structure. • The PNFAs@VNPs has the advantages of Faraday and intercalation type pseudocapacitor. • The PNFAs@VNPs shows a specific capacitance of 950 F g−1at 5 mV s−1. • The PNFAs@VNPs supercapacitor has an energy density of 67.0 W h kg−1 at 550 W kg−1. [ABSTRACT FROM AUTHOR]

V 2 O 5 nanobelt arrays (VNBAs) is fabricated on Ni foam by using an easy hydrothermal route and then NiO nanosheet arrays (NNSAs) is grown on VNBAs by using a simple chemical bath deposition approach to form VNBAs/NNSAs composite. It is found that the monocrystalline VNBAs with a lamellar structure is uniformly distributed on nickel foam and the polystalline NNSAs with a close packed structure is closely covered on the VNBAs. CV, GCD, EIS and CA electrochemical techniques are used to test the supercapacitive properties of the VNBAs/NNSAs composite. The single electrode displays a high specific capacity of 875 F g−1, a good cycling stability of 96.1%, a small charge transfer resistance of 1.32 Ω and a rapid ion diffusivity of 2.5 × 10−8 cm2 s−1. The symmetric supercapacitor combined by the VNBAs/NNSAs displays a large energy density of 120.1 W h kg−1 at 400 W kg−1 and it retains 68.3 W h kg−1 at 8000 W kg−1. The VNBAs/NNSAs composite with high electrochemical performance is a potential supercapacitor electrode material. [Display omitted] • The V 2 O 5 nanobelt arrays (VNBAs) is successfully prepared on a nickel foam. • The NiO nanosheet arrays (NNSAs) is compounded on the VNBAs to form a hierarchy. • The VNBAs/NNSAs shows a high specific capacitance of 875 F g−1 at 5 mV s−1. • The VNBAs/NNSAs has an energy density of 120.1 W h kg−1 at 400 W kg−1. • The high performance of the VNBAs/NNSAs are ascribed to its synergistic effect. [ABSTRACT FROM AUTHOR]

Abstract WO 3 nano-fibers with super large aspect ratio are synthesized on a Cu conductive current collector by using a simple hydrothermal method. The as-prepared WO 3 nano-fibers can accommodate a large number of electrolyte ions and provide a rapid route for the migration of electrons and electrolyte ions due to its direct growth, high specific surface area, and one dimensional (1D) pipeline structure. The WO 3 nano-fibers exhibit excellent cyclic reversibility (98% at 1.0 A g−1), good cycling stability (93% after 5000 cycles), high specific capacitance (436 F g−1 at 1.0 A g−1) and low charge transfer resistance (29 Ω). After the WO 3 nano-fibers are assembled into a symmetric supercapacitor, the symmetric supercapacitor device has a wide effective operating range of 0–1.8 V and high energy density of 99.0 W h kg−1 at the power density of 450 W kg−1. The good electrochemical performances of as-prepared WO 3 nano-fibers make it an attractive candidate for high energy storage systems and promising supercapacitor electrode material. Graphical abstract Image 1 Highlights • WO 3 nano-fibers with super large aspect ratio are prepared directly on a Cu foil. • The WO 3 nano-fibers exhibit a high specific capacitance of 436 F g−1 at 1.0 A g−1. • The WO 3 nano-fibers have a high energy density of 99.0 W h kg−1 at 450 W kg−1. • The good properties of WO 3 nano-fibers are ascribed to their special structure. [ABSTRACT FROM AUTHOR]

Abstract We report a heterojunction composite of V 2 O 5 nanobelt arrays/TiO 2 nanoflake arrays grown directly on nickel foam. The morphology evolution and growth mechanism of TiO 2 nanoflake arrays on V 2 O 5 nanobelt arrays are investigated in detail. The heterojunction composite nano-arrays have a large specific capacitance of 587 F g−1 at a current density of 0.5 A g−1, a high coulombic efficiency (>92%), an excellent cycle stability (92%) after 5000 cycles and a low charge transfer resistance of 2.6 Ω. When the heterojunction composite nano-arrays are assembled into symmetric supercapacitor, the device shows a high energy density of 100.8 W h kg−1 at a power density of 399 W kg−1. The high supercapacitive performance is attributed to their direct growth on conductive current collector and the synergistic effect of V 2 O 5 and TiO 2. Graphical abstract Image 1 Highlights • V 2 O 5 nanobelt arrays (VNBs) is prepared directly on a nickel foam. • TiO 2 nanoflake arrays (TNFs) is prepared on VNBs to form a heterojunction. • The VNBs/TNFs shows a high specific capacitance of 587 F g−1 at 0.5 A g−1. • The VNBs/TNFs exhibits a high energy density of 100.8 W h kg−1 at 399 W kg−1. • The high performance of VNBs/TNFs is ascribed to their synergistic effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • V 2 O 5 nanobelt arrays@RuO 2 nanosheet arrays (VNBs@RNSs) is prepared on a nickel foam. • The VNBs@RNSs electrode shows a specific capacitance of 971F g−1 at 5 mV s−1. • The VNBs@RNSs supercapacitor has an energy density of 174.2 W h kg−1 at 450 W kg−1. • The cyclic steadiness of the supercapacitor is retained at 80.4% after 10,000 cycles. • The high performance of VNBs@RNSs is ascribed to their synergistic effect. V 2 O 5 nanobelt arrays (VNBs) are directly synthesized on porous nickel as the primary structure, and then the VNBs are completely covered by RuO 2 nanosheets (RNSs) as the secondary structure to create a core–shell heterojunction. The as-prepared VNBs@RNSs core–shell heterojunction is systematically researched through SEM, EDS, XRD, XPS and TEM, and the growth process is investigated in detail by sampling at different time. The VNBs@RNSs has a superb specific capacitive value of 971F g−1 at a voltage scanning speed of 5 mV s−1, a better cyclic steadiness of 80.4 % after recycling 10,000 times, a small charge transferring resistance value of 1.8 Ω and a fast effective diffusion coefficient of 1.01 × 10−8 cm2 s−1 calculated by CV, GCD, AC impedance and CA electrochemical techniques in a three-electrode testing system. A symmetrical electrochemical capacitor assembled by the as-prepared VNBs@RNSs electrode material has a superior energy density of 174.2 W h kg−1 at a power density of 450 W kg−1 and still retains 95.9 W h kg−1 at 9000 W kg−1 in a two-electrode testing system. The improved supercapacitive performance makes the VNBs@RNSs as a superior electrode material for supercapacitor. [ABSTRACT FROM AUTHOR]

[Display omitted] • V 2 O 5 nanobelt arrays@RuO 2 nanosheet arrays (VNBs@RNSs) is prepared on a nickel foam. • The VNBs@RNSs electrode shows a specific capacitance of 971F g−1 at 5 mV s−1. • The VNBs@RNSs supercapacitor has an energy density of 174.2 W h kg−1 at 450 W kg−1. • The cyclic steadiness of the supercapacitor is retained at 80.4% after 10,000 cycles. • The high performance of VNBs@RNSs is ascribed to their synergistic effect. V 2 O 5 nanobelt arrays (VNBs) are directly synthesized on porous nickel as the primary structure, and then the VNBs are completely covered by RuO 2 nanosheets (RNSs) as the secondary structure to create a core–shell heterojunction. The as-prepared VNBs@RNSs core–shell heterojunction is systematically researched through SEM, EDS, XRD, XPS and TEM, and the growth process is investigated in detail by sampling at different time. The VNBs@RNSs has a superb specific capacitive value of 971F g−1 at a voltage scanning speed of 5 mV s−1, a better cyclic steadiness of 80.4 % after recycling 10,000 times, a small charge transferring resistance value of 1.8 Ω and a fast effective diffusion coefficient of 1.01 × 10−8 cm2 s−1 calculated by CV, GCD, AC impedance and CA electrochemical techniques in a three-electrode testing system. A symmetrical electrochemical capacitor assembled by the as-prepared VNBs@RNSs electrode material has a superior energy density of 174.2 W h kg−1 at a power density of 450 W kg−1 and still retains 95.9 W h kg−1 at 9000 W kg−1 in a two-electrode testing system. The improved supercapacitive performance makes the VNBs@RNSs as a superior electrode material for supercapacitor. [ABSTRACT FROM AUTHOR]

In this paper, four NiO nano-arrays with different morphology on nickel foam were synthesized by a hydrothermal approach. It is found that the porous single crystal NiO nanoflake array (PNFA) holds superior electrochemical properties, better than the other three samples. The specific capacitance of the PNFA obtained from the cyclic voltammetry curve was 716 F g−1 and that derived from the galvanostatic charge-discharge curve was 589 F g−1 in three-electrode system. The cycling stability of the PNFA could retain as high as 92.4% after 5000 cycles. When the PNFA was assembled into a symmetric supercapacitor, the PNFA//PNFA device exhibited an energy density of 39.3 W h kg−1 (at 550 W kg−1) and could retain 13.2 W h kg−1 (at 11,000 W kg−1) in two-electrode system. Furthermore, the SEM, XRD, TEM and XPS results prove that the PNFA is a special porous single crystal structure, which combines the advantages of the cross-linked single crystal structure for facilitating electron transfer and the porous structure providing more interfaces for insertion/exit of electrolyte ions from the active material. It indicates that the PNFA is a potential electrode material for supercapacitors. [Display omitted] • Porous single crystal NiO nanoflake array (PNFA) is directly grown on nickel foam. • The PNFA is prepared by a facile hydrothermal method following an annealing process. • The PNFA combines the advantages of porous material and single crystal material. • The PNFA shows a specific capacitance of 716 F g−1 at a scan rate of 5 mV/s. • The PNFA//PNFA supercapacitor has an energy density of 39.3 W h kg−1 at 550 W kg−1. [ABSTRACT FROM AUTHOR]