Search

Three-dimensional (3D) porous MnO 2 array assembled from one-dimensional tubular MnO 2 with ultrathin sheets were fabricated by a one-pot hydrothermal method using polycarbonate membrane as the template. The diameter and thickness of nanotubes can be controlled by the membrane. Detailed electrochemical characterization reveals that the porous MnO 2 arrays exhibited good rate performance and cycle life. The highest specific capacitance in a three-electrode system was 411.9 F g −1 at a current density of 0.25 A g −1 . An asymmetric supercapacitor with porous MnO 2 nanotubes arrays as the positive electrode and activated graphene as the negative electrode yielded an energy density of 22.6 Wh kg −1 at a power density of 225.3 W kg −1 . The capacitive performance was correlated with the hierarchical structure of the porous MnO 2 nanotubes. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we developed a one-pot approach to fabricate CoFe2O4/FeOOH nanocomposites without any surfactant. By tailoring the urea concentration, flower-like nanostructures of CoFe2O4/FeOOH nanocomposites can be obtained. The electrochemical properties of the CoFe2O4/FeOOH electrodes were elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 6M KOH electrolyte. Flower-like CoFe2O4/FeOOH exhibited a specific capacitance of 332.4Fg−1 at the current density of 0.5Ag−1, and excellent cycling stability (91.3% retention after 1000 cycles, 5Ag−1). These findings suggested that this facile synthetic strategy could be useful to design and synthesize hierarchical electrode nanocomposites with enhanced supercapacitive performance. [Copyright &y& Elsevier]

Abstract: The hierarchically porous NiO-modified diatomite structures are prepared for the first time by a one-pot hydrothermal method, which possess a moss-like structure assembled from NiO nanofibres arrays. Furthermore, the electrochemical properties of the NiO-modified diatomite electrodes are elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 1M KOH electrolyte. The electrochemical results demonstrate that this unique NiO-modified diatomite structures exhibit a specific capacitance of 218.7Fg−1 and excellent cycling stability (90.61% retention after 1000 cycles). Such high-performance capacitive behavior indicates that the low-cost NiO-modified diatomite structures are promising electrode materials for the fabrication of supercapacitors. [Copyright &y& Elsevier]

Supercapacitors have drawn intensive attention in recent years due to their high specific power, long cycle life, and ability to fully fill the need for capacitors and batteries of hybrid energy applications. Electrodes of nanomaterials have shown superior electrochemical properties in performing high-performance supercapacitors. This feature article describes our recent progress in designing on different nanostructure of birnessite-type of manganese oxide-based materials for these applications. In order to fully understand the potential of manganese oxide-based electrode nanomaterials, sketchy appreciation of these morphology ranging from different dimensions and material properties are carried out critically, which may serve as a guidance for further development of fabricating supercapacitor electrode. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we developed a simple and cost-effective approach to prepare the hierarchical NiO/CuO nanocomposite without any surfactant. The morphology and structure of the hybrid nanostructure was examined by focus ion beam scanning electron microscopy (FIB/SEM), X-ray diffraction spectroscopy (XRD) and high-resolution transmission electron microscopy (HRTEM). Furthermore, the electrochemical properties of the hierarchical NiO/CuO nanocomposite electrodes were elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 6M KOH electrolyte. The electrochemical results demonstrated that this unique NiO/CuO nanostructure exhibited a specific capacitance of 280Fg−1 and excellent cycling stability (91.4% retention after 3000 cycles). The remarkable electrochemical performance coupled with the facile synthesis of the hierarchical NiO/CuO nanocomposite indicated the great application potential in supercapacitors. [Copyright &y& Elsevier]

Graphical abstract Naturally abundant diatomite was used as a biotemplate for the large-scale production of 3D N-doped graphene@MnO 2 porous structure for use in high-performance supercapacitor and oxygen reduction reaction catalyst. Abstract Natural diatomite with abundant pores was used as a biotemplate for the massive production of three-dimensional (3D) porous graphene by chemical vapor deposition method. Subsequent template removal and nitrogen doping treatment yield nitrogen doped 3D graphene with preserved shape and complex internal features of the diatomite. After further deposition with MnO 2 nanosheets, the N-doped 3D graphene@MnO 2 (N-G@MnO 2) hybrid exhibited excellent supercapacitor and good oxygen reduction reaction (ORR) performance. Accordingly, the porous N-G@MnO 2 electrode exhibited a high specific capacitance (411.5 F g−1) and a good cycling performance (88.3% capacitance retention after 4000 charge/discharge cycling test). When tested in a two-electrode configuration, N-G@MnO 2 achieved a wide potential window up to 1.8 V with a high energy density of 46.1 Wh kg−1. Furthermore, the as-prepared N-G@MnO 2 showed good performance in oxygen reduction reaction, which is comparable to those of commercially available Pt/C electrode. The enhanced capacitive and electrocatalytic properties and stability is due to the synergistic interactions between the porous 3D graphene and MnO 2 nanosheets. The results indicate that the 3D N-G@MnO 2 could be useful for supercapacitor and ORR catalyst. [ABSTRACT FROM AUTHOR]

A rational and hierarchical Diatom@CuO@MnO 2 hybrid was fabricated via a facile electroless copper plating technology, following by a one-pot hydrothermal reaction with KMnO 4 . Such unique architecture acts as a supercapacitor electrode, which exhibits a high specific capacitance (240 F g −1 at a current density of 0.5 A g −1 ), good rate capability (58.3% retention when the current density increases from 0.5 to 5 A g −1 ), and excellent electrochemical cycling stability (91.2% retention of the initial specific capacitance after 4000 cycles at a current density of 2 A g −1 ). The impressive electrochemical performance of this Diatom@CuO@MnO 2 electrode ascribed to the synergistic effect between the CuO particles and MnO 2 nanosheets. Therefore, it can be expected that this unique Diatom@CuO@MnO 2 electrode may have great promise for the application in supercapacitors. [ABSTRACT FROM AUTHOR]

Vertically assembled two-dimentional materials have great scientific and technological promise. In this work, altrathin atom doped graphitic carbon nitride (g-C 3 N 4 ) was synthesised via thermal treatment of thiourea and KBr/NaBr. Free-standing manganese dioxide nanoflakes were uniformly grown on K/Na doped g-C 3 N 4 through hydrothermal reaction. The K doped g-C 3 N 4 @ MnO 2 has a specific capacitance twice higher than that of pure g-C 3 N 4 @ MnO 2 . This unique design brought excellent specific capacitance (375 F g −1 ) and cycle stability, which showed that atom doping is an effective approach to enhance electrochemical performance. In addition, the low cost, facial synthesis and small amount of addings make this strategy an optimized approach to construct g-C 3 N 4 based electrode materials. [ABSTRACT FROM AUTHOR]

A novel copper/nickel-based manganese dioxide core-shell nanostructure can be prepared for supercapacitor electrodes using facile hydrothermal methods. Attributed to Kirkendall-type diffusion process, the “core” can transfer to hollow structure during the reaction interestingly. The faradic reaction occurs effectively in the electrode and electrolyte due to the high conductivity of Cu/Ni and large hollow channel structure. As a result, the electrode displays a high specific capacitance (374 F g −1 at current density of 0.25 A g −1 ), fine cycling stability (86.9% retention after 3000 cycles) and outstanding rate capability. These interesting findings suggest that the hybrid material can be a promising candidate for supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Low cost, non-toxic nanomaterials and their controllable synthesis are highly demanded in the field of supercapacitors. In this work, nanoneedle and nanosheet-like porous NiCo 2 O 4 architectures were directly fabricated on graphitic carbon nitride (g-C 3 N 4 ), indicating structure dependence on their capacitive performances. Electrochemical performances show that nanoneedle-assembled NiCo 2 O 4 /g-C 3 N 4 exhibits higher specific capacitance (253 F g −1 at a current density of 2 A g −1 ), while nanosheet-assembled NiCo 2 O 4 /g-C 3 N 4 possesses a better cycling durability (101.4% capacitance after 1000 cycles) in a three-electrode configuration. Further studies indicate that these electrochemical differences are related to the structure and electrochemical impedance of nanocomposites. [ABSTRACT FROM AUTHOR]

A simple, template-free strategy without organic dispersant or capping agent is developed to synthesize a novel monodispersed NiO@MnO 2 nanostructure as powdery electrode for supercapacitors. The first step in the synthesis involves the NaOH mediated evolution of Ni(OH) 2 nanosheets, further leading to the formation of NiO structure with different features. After calcination in air, via self-decomposition of KMnO 4 solution in a lower concentration, MnO 2 nanoflakes are elaborately grafted along the petal of NiO microspheres to form core–shell nanostructures, enhancing specific surface area and homogenizing pore-size distribution of NiO@MnO 2 . Owing to the hierarchical core–shell heterostructure configuration with rich mesoporous and synergetic contribution from the NiO core and MnO 2 shell, NiO@MnO 2 exhibits relatively high specific capacitance and good rate capability, which are better than those of the individual NiO structure. The enhanced performance of the NiO@MnO 2 core–shell structure demonstrates that integrated spherical structure constructed by two high capacitance materials is a rational design, which holds definite potential in supercapacitors and other kinds of energy storage systems. [ABSTRACT FROM AUTHOR]

This work demonstrates a new and simple approach for fabrication a complex three-dimensional (3-D) composite for supercapacitor based on hollow diatom silica structures combined with interconnected coatings of TiO 2 nanospheres and MnO 2 mesoporous nanosheets (diatomite@TiO 2 @MnO 2 ) . The coating process is based on hydrolysis and metathetic reaction of TiF 4 precursor followed by the reaction with KMnO 4, which allows the coating of internal and external surface of diatom hollow structure with TiO 2 and MnO 2 layers. It was demonstrated that the introduction of anatase TiO 2 layer on the 3-D diatomite@TiO 2 @MnO 2 electrodes provides a superior performance in terms of the specific capacitance, rate capability and resistance, showing critical role of an additional conductive layer on diatom surface. Moreover, by virtue of the unique 3-D structure, diatomite@TiO 2 @MnO 2 electrode also displays a long cyclic stability (retain 94.1% after 2000 cycling) and a high coulombic efficiency (retain 98.2%-99.6% during 2000 cycling). The presented results show an enhanced supercapacitor behavior of the diatomite@TiO 2 @MnO 2 electrodes prepared using a low-cost natural diatomite material and simple scalable process and confirm their evident potential for energy storage/conversion applications. [ABSTRACT FROM AUTHOR]

Ultrathin MnO 2 nanosheets-built nanotubes have been fabricated via a large-scale chemical etching method. The diameter and thickness of MnO 2 nanotubes can be controlled by fine-tuning the concentration of KMnO 4 solution, and the relationship between electrochemical properties and different wall thickness is notably investigated. Besides, the MnO 2 nanotubes possess a high surface area of 179.5 m 2 g −1 and lots of mesopores. Such unique features are beneficial for providing easy access of the electrolyte to the structure and shortening the diffusion distance of ions. More significantly, recyclable copper ions after etching can be used to synthesize Cu nanowires again. The MnO 2 nanotubes in a three-electrode system display much high specific capacitance (377.5 F g −1 at current density of 0.25 A g −1 ), good rate performance. Moreover, an asymmetric supercapacitor on the basis of MnO 2 nanotubes as the positive electrode and activated graphenes (AG) as the negative electrode produced an energy density of 22.68 Wh kg −1 and a maximum power density of 4.5 kW kg −1 . These attractive discoveries suggest that it can be an aussichtsreich candidate as an efficient supercapacitive electrode. [ABSTRACT FROM AUTHOR]

We demonstrate a novel preparative strategy for the well-controlled MnCo 2 O 4.5 @MnO 2 hierarchical nanostructures. Both δ-MnO 2 nanosheets and α-MnO 2 nanorods can uniformly decorate the surface of MnCo 2 O 4.5 nanowires to form core–shell heterostructures. Detailed electrochemical characterization reveals that MnCo 2 O 4.5 @δ-MnO 2 pattern exhibits not only high specific capacitance of 357.5 F g −1 at a scan rate of 0.5 A g −1 , but also good cycle stability (97% capacitance retention after 1000 cycles at a scan rate of 5 A g −1 ), which make it have a promising application as a supercapacitor electrode material. [ABSTRACT FROM AUTHOR]

Abstract: In this work, dandelion-like NiCo2O4 mesoporous microspheres were uniformly assembled from slim nanowires via a large-scale and template-free method. The Brunauer–Emmett–Teller (BET) surface area of NiCo2O4 microspheres was determined to be about 35.2m2 g−1 with dominant pore diameter of 10.9nm and narrow size distribution of 8–20nm. Furthermore, the electrochemical properties of NiCo2O4 microspheres were evaluated by cycle voltammetric (CV) and galvanostatic charge–discharge (GCD) measurements. The results demonstrated that the NiCo2O4 microspheres exhibited high specific capacitance (372Fg−1 at 1Ag−1), good rate capability, and excellent cycling stability (88.3% retention after 2000 cycles). In principle, this synthetic approach could be extended for the fabrication of other microstructure materials for promising electrode candidates in energy storage devices. [Copyright &y& Elsevier]