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Highlights • Highly porous carbon nanofoams (CNFs) were synthesized by a vapor plasma process. • It has a 3D hierarchical morphology, continuous porosity, and high surface area. • Annealing and N doping enhanced electrical and electrochemical properties of CNFs. • The N doped CNFs showed high specific capacitance and excellent cycling stability. Abstract Highly porous carbon nanofoams (CNFs) could be massively synthesized at room temperature from acetylene gas precursor by a plasma-enhanced chemical vapor deposition technique. The synthesized CNFs had a three-dimensional framework structure composed of aggregations of nano-sized spherical carbon particles, in which the open-connected micron- and nano-pores were hierarchically distributed. Afterwards, thermal treatment and nitrogen doping process were conducted to enhance both electrical conductivity and electrochemical properties of the CNFs. The nitrogen-doped CNFs (N-CNFs) exhibited very high specific surface area of up to 920.4 m2 g−1 and a pore volume of approximately 0.70 cm3 g−1. Due to their hierarchical porous structure, large ion-accessible surface area, and good conductivity for fast ion sorption and electron transfer, the N-CNFs exhibited excellent electrochemical performance for supercapacitor application, such as high specific capacitance of 362.6F g−1 at a current density of 1 A g−1 and super stability in cycle life test. In addition, a symmetric supercapacitor assembled with N-CNFs could deliver a maximum energy density of 24.4 Wh kg−1 and a power density of 8.8 kW kg−1. [ABSTRACT FROM AUTHOR]

Abstract Polycrystalline and mesoporous bismuth oxide (Bi 2 O 3) micro-sponge-balls of 4–7 μm in diameter comprising of 58–65 (±2) nm upright standing petals, separated by 100–700 (±50) nm crevices, are synthesized directly onto 3D Ni-foam at room-temperature (27 °C) using Tritonx-100 surfactant-mediated soft wet chemical method. After knowing the phase purity, surface area, pore-size distribution, micro-sponge-ball-type surface morphology, elemental analysis and binding energy confirmations of Bi 2 O 3 , a material with quasi-faradaic redox reactions responsible for supercapattery type behavior, are measured and explored. At a low scan rate, the specific capacitance of Bi 2 O 3 sponge-ball electrode, measured from 0.4 to 1.80 A g−1 current density, decreases from 559 to 211 F g−1 which is equivalent to a capacity from 155 to 58 mAh.g−1. An asymmetric supercapacitor (ASC) device assembly of Bi 2 O 3 sponge-ball electrode with graphite i.e. Bi 2 O 3 //graphite demonstrates excellent electrochemical properties with 8 Wh kg−1 energy density at 2040 W kg−1 power density, and about 80% cycling retention over 5000 redox cycle operations. A demonstration of LED with full-bright intensity during discharge process of the Bi 2 O 3 //graphite ASC device suggests its practical potentiality and industrial viability. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Since the discovery of two-dimensional (2D) graphene, a new class of 2D materials with excellent electrical conductivity has recently been attracting attention in studying promising electrode materials in energy storage applications. Herein, bismuth oxychloride nanosheets-immobilised Ti 3 C 2 T x MXene material (TCBOC) is synthesised by a facile and cost-effective chemical bath deposition (CBD) route. The bismuth oxychloride (BiOCl) nanosheets are grown and immobilised on surfaces of Ti 3 C 2 T x -MXene flakes. An electrode based on the TCBOC nanocomposite exhibited a remarkably volumetric specific capacitance of 396.5 F cm -3  at 1 A g −1 and 228.0 F cm -3  at 15 A g −1 . Furthermore, a symmetric supercapacitor (SSC) assembled using TCBOC material proves to have a high energy density of 15.2 Wh kg −1 at a power density of 567.4 W kg −1 compared to SSCs using previously reported Ti 3 C 2 T x MXene materials. The SSC shows cycle life retention of 85.0% after 5000 cycles (at 5 A g −1 ). The enhanced capacitive performance is attributed to the increased surface area due to BiOCl nanosheets anchored on a 2D MXene surface, the activities of BiOCl sheets, and the excellent conductivity of a Ti 3 C 2 T x MXene material. [ABSTRACT FROM AUTHOR]

Hierarchical chestnut-like manganese cobalt oxide (MnCo 2 O 4 ) nanoneedles (NNs) are successfully grown on nickel foam using a facile and cost-effective hydrothermal method. High resolution TEM image further verifies that the chestnut-like MnCo 2 O 4 structure is assembled by numerous 1D MnCo 2 O 4 nanoneedles, which are formed by numerous interconnected MnCo 2 O 4 nanoparticles with grain diameter of ∼10 nm. The MnCo 2 O 4 electrode exhibits high specific capacitance of 1535 F g −1 at 1 A g −1 and good rate capability (950 F g −1 at 10 A g −1 ) in a 6 M KOH electrolyte. An asymmetric supercapacitor is fabricated using MnCo 2 O 4 NNs on Ni foam (MnCo 2 O 4 NNs/NF) as the positive electrode and graphene/NF as the negative electrode. The device shows an operation voltage of 1.5 V and delivers a high energy density of ∼60.4 Wh kg −1 at a power density of ∼375 W kg −1 . Moreover, the device exhibits an excellent cycling stability of 94.3% capacitance retention after 12000 cycles at 30 A g −1 . This work demonstrates that hierarchical chestnut-like MnCo 2 O 4 NNs could be a promising electrode for the high performance energy storage devices. [ABSTRACT FROM AUTHOR]