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Previous research on iron oxides/hydroxides has focused on the crystalline rather than the amorphous phase, despite that the latter could have superior electrochemical activity due to the disordered structure. In this work, a simple and scalable synthesis route is developed to prepare amorphous FeOOH quantum dots (QDs) and FeOOH QDs/graphene hybrid nanosheets. The hybrid nanosheets possess a unique heterostructure, comprising a continuous mesoporous FeOOH nanofilm tightly anchored on the graphene surface. The amorphous FeOOH/graphene hybrid nanosheets exhibit superior pseudocapacitive performance, which largely outperforms the crystalline iron oxides/hydroxides-based materials. In the voltage range between −0.8 and 0 V versus Ag/AgCl, the amorphous FeOOH/graphene composite electrode exhibits a large specific capacitance of about 365 F g−1, outstanding cycle performance (89.7% capacitance retention after 20 000 cycles), and excellent rate capability (189 F g−1 at a current density of 128 A g−1). When the lower cutoff voltage is extended to −1.0 and −1.25 V, the specific capacitance of the amorphous FeOOH/graphene composite electrode can be increased to 403 and 1243 F g−1, respectively, which, however, compromises the rate capability and cycle performance. This work brings new opportunities to design high-performance electrode materials for supercapacitors, especially for amorphous oxides/hydroxides-based materials. [ABSTRACT FROM AUTHOR]

A novel core–shell structured Co 11 (HPO 3 ) 8 (OH) 6 –Co 3 O 4 hybrid material was synthesized in a hydrothermal condition from the microporous Co 11 (HPO 3 ) 8 (OH) 6 microrod precursor. Due to the unique nano/microstructures, the assembled asymmetric all-solid-state supercapacitor (Co 11 (HPO 3 ) 8 (OH) 6 –Co 3 O 4 and graphene) showed a high gravimetric specific capacitance of 1.84 F cm −3 at 0.5 mA cm −2 and an excellent cycling stability with only 1.3% ca decay after 3000 cycling. The device delivered a maximum power density of 105 mW cm −3 at a current density of 1.5 mA cm −2 and possessed a maximum volumetric energy density of 0.48 mW h cm −3 at a current density of 0.5 mA cm −2 . The device also exhibited excellent flexibility. [ABSTRACT FROM AUTHOR]

1D Co 2.18 Ni 0.82 Si 2 O 5 (OH) 4 architectures assembled by ultrathin nanoflakes are synthesized for the first time by a hydrothermal method. We present a self-reacting template method to synthesize 1D Co 2.18 Ni 0.82 Si 2 O 5 (OH) 4 architectures using Ni(SO 4 ) 0.3 (OH) 1.4 nanobelts. A high-performance flexible asymmetric solid-state supercapacitor can be successfully fabricated based on the 1D Co 2.18 Ni 0.82 Si 2 O 5 (OH) 4 architectures and graphene nanosheets. Interestingly, the as-assembled 1D Co 2.18 Ni 0.82 Si 2 O 5 (OH) 4 architectures//Graphene nanosheets asymmetric solid-state supercapacitor can achieve a maximum energy density of 0.496 mWh cm −3 , which is higher than most of reported solid state supercapacitors. Additionally, the device shows high cycle stability for 10,000 cycles. These features make the 1D Co 2.18 Ni 0.82 Si 2 O 5 (OH) 4 architectures as one of the most promising candidates for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a novel macro–microporous architecture is successfully constructed in a honeycomb-like structure by directly using rape seed shell via impregation-activation route. This approach permits the high specific surface area (SSA) and a unique hierarchical porous structure which consists of interconnected macroporous skeleton and a significant microporosity. The unique honeycomb-like network combined with high specific surface area is favorable for charging the electric double-layer. The resulting carbon is highly suitable as electrodes of electric double layer capacitors, with remarkable values of capacitance of up to 225Fg−1 at a current density of 1Ag−1 in 2M KOH electrolyte. Therefore, the as-prepared carbon can be a potential candidate for supercapacitors. [Copyright &y& Elsevier]

Abstract: Two kinds of functionalized graphene sheets were produced by thermal exfoliation of graphite oxide. The first kind of functionalized graphene sheets was obtained by thermal exfoliation of graphite oxide at low temperature in air. The second kind was prepared by carbonization of the first kind of functionalized graphene sheets at higher temperature in N2. Scanning electron microscopy images show that both two kinds of samples possess nanoporous structures. The results of N2 adsorption–desorption analysis indicate that both of two kinds of samples have high BET surface areas. Moreover, the second kind of functionalized graphene sheets has a relatively higher BET surface area. The results of electrochemical tests is as follows: the specific capacitance values of the first kind of functionalized graphene sheets in aqueous KOH electrolyte are about 230Fg−1; the specific capacitance values of the second kind of functionalized graphene sheets with higher BET surface areas are only about 100Fg−1; however, compared with the first kind of functionalized graphene sheets, the second kind has a higher capacitance retention at large current density because of its good conductive behaviors; furthermore, in non-aqueous EC/DEC electrolyte, the specific capacitance values of the first kind sample and the second kind sample are about 73Fg−1 and 36Fg−1, respectively. [Copyright &y& Elsevier]

Designing and preparing kinetically stable metal–organic frameworks through ligand functionalization can effectively improve their supercapacitive performances. Herein, we have successfully synthesized a novel polythreaded Co-based MOF by choosing a flexible N-donor ligand and a rigid multicarboxylate linker, [Co(HTATB)(dib)]·2H2O (1), where dib is the flexible N-donor 1,4-di(1H-imidazol-1-yl)butane linker and HTATB is the deprotonation mode from 4,4′,4′′-s-triazine-2,4,6-triyl-tribenzoic acid. The bulk Co-MOFs crystals and the corresponding nanorod powders have been evaluated as electrode materials for supercapacitors. The maximum gravimetric capacitance of the nanorod electrode is 2405 F g−1 at 0.75 A g−1 in 4 M KOH, which is higher than 1 M and 6 M KOH solution and seven times larger than that of the bulk-crystal electrode. Furthermore, the nanorod electrode also exhibits excellent Coulombic efficiency (92.2%), rate capability (53.5% after 20 times increase) and good cycling performance (93.5% after 3000 continuous cycles). The excellent electrochemical property may be ascribed to the 3D networks constructed from 2D entangled layered structures facilitating electron transport, sufficient interlayer spaces available for the storage and diffusion of OH− ions, and the small-size effect of the nanorods. Further, the dye adsorption performance of crystalline 1 for methyl orange and Congo red has also been investigated. [ABSTRACT FROM AUTHOR]

A template-free hydrothermal method is developed to prepare hierarchical hollow precursors. An inside-out Ostwald ripening mechanism is proposed to explain the formation of the hollow structure. After the calcination in the air, hierarchically meso/macroporous NaCoPO4-Co3O4 hollow microspheres can easily be obtained. When being evaluated as electrode materials for a supercapacitor, the hierarchically porous NaCoPO4-Co3O4 hollow microspheres electrode shows a specific capacitance of 268 F g−1 at 0.8 A g−1 and offers a good cycle life. More importantly, the obtained materials are successfully applied to fabricate flexible solid-state asymmetric supercapacitors. The device exhibits a specific capacitance of 28.6 mF cm−2 at 0.1 mA cm−2, a good cycling stability with only 5.5% loss of capacitance after 5000 cycles, and good mechanical flexibility under different bending angles, which confirms that the hierarchically porous NaCoPO4-Co3O4 hollow microspheres are promising active materials for the flexible supercapacitor. [ABSTRACT FROM AUTHOR]

For building high-energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe2O3 has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe2O3-based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe2O3 quantum dots (QDs, ≈2 nm) decorated on functionalized graphene-sheets (FGS) is prepared by a facile and scalable method. The Fe2O3 QDs/FGS composites exhibit a large specific capacitance up to 347 F g−1 in 1 m Na2SO4 between -1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe2O3/FGS as anode and MnO2/FGS as cathode in 1 m Na2SO4 aqueous electrolyte. The Fe2O3/FGS//MnO2/FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg−1 at a power density of 100 W kg−1 as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe2O3 QDs/FGS composites make them promising as anode materials for high-performance asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]

Carbon-coated Mn3O4 nanowires (Mn3O4@C NWs) have been synthesized by the reduction of well-shaped carbon-coated bixbyite networks and characterized by TEM, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical experiments. To assess the properties of 1D carbon-coated nanowires for their use in supercapacitors, cyclic voltammetry and galvanostatic charging-discharging measurements were performed. Mn3O4@C NWs could be charged and discharged faster and had higher capacitance than bare Mn3O4 nanostructures and other commercial materials. The capacitance of the Mn3O4@C NWs was 92 % retained after 3000 cycles at a charging rate of 5 A g−1. This improvement can be attributed to the carbon shells, which promote fast Faradaic charging and discharging of the interior Mn3O4 core and also act as barriers to protect the inner core. These Mn3O4@C NWs could be a promising candidate material for high-capacity, low-cost, and environmentally friendly electrodes for supercapacitors. In addition, the magnetic properties of the as-synthesized samples are also reported to investigate the influence of the carbon coating. [ABSTRACT FROM AUTHOR]