Ting Lin

In situ growth of burl-like nickel cobalt sulfide on carbon fibers as high-performance supercapacitors

Nickel cobalt sulfide (NiCo2S4), a recently reported novel electrode material, has a higher electric conductivity than that of NiCo2O4. We describe a facile one-step route to the development of burl-like NiCo2S4 on carbon fiber paper/cloth (CFP/CFC) used as electrodes for supercapacitors. The influence of the carbon substrate on the crystal structure and electrochemical performance of the NiCo2S4 electrodes is evaluated. We obtained a pure phase of NiCo2S4 over a CFP substrate, whereas, a mixed phase over a CFC substrate. Superior pseudocapacitive performance is achieved over NiCo2S4/CFP with a large specific capacitance of 0.83 F cm−2 at a high current density of 25 mA cm−2. The capacitance loss is 24.1% after 5000 cycles at a current density of 20 mA cm−2, displaying good cyclability and high rate capability.

Controlled synthesis of nanostructured manganese oxide: crystalline evolution and catalytic activities

A hydrothermal process has been used to synthesize manganese oxides of various crystalline structures and morphologies, such as α-, β-, γ-MnO2, MnOOH and Mn3O4. The nanostructured materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and hydrogen temperature-programmed reduction (H2-TPR) techniques. The crystalline evolution mechanism of converting β-MnO2 or MnOOH to α-MnO2 was studied. The crystalline-dependent effect of the nanostructured manganese oxides was explored by using toluene combustion as a probe reaction. Results indicated that the catalytic activity of α-MnO2 with ultra-long nanowires is higher than that of manganese oxides with other crystalline structures. The catalytic activity was correlated with the H2-TPR and XPS results.

Multifunctional free-standing membrane from the self-assembly of ultralong MnO2 nanowires.

In this work, we report the preparation of a free-standing membrane with strong mechanical stability and flexibility through a facile vacuum filtration approach. A field-emission scanning electron microscopy image demonstrates that the membrane composed of MnO2 nanowires is 50 nm in width and up to 100 μm long and the nanowires are assembled in parallel into bundles. A possible formation mechanism for the ultralong nanowires and the free-standing membrane has been proposed. Meanwhile, the properties of the membrane could be controlled by incorporating different materials to achieve composite membranes. In order to demonstrate the broad applicability of the MnO2 membrane, we fabricate a variety of composite membranes exhibiting various novel properties including magnetism and reversibly switchable wettability between hydrophilicity and hydrophobicity through various material modification, including CoFe2O4 nanoparticles and organic triethoxy(octyl)silane. Furthermore, the free-standing membrane could also simultaneously be functionalized with two materials, which reveal multiple properties. The synthesis method of a free-standing MnO2 membrane is simple and environmentally friendly, and it is easily scalable for industry. These composite membranes constitute a significant contribution to advanced technology.

A facile one-pot hydrothermal synthesis of branched α-MnO2 nanorods for supercapacitor application

Branched α-MnO2 nanorods are synthesized using a facile hydrothermal method without surfactants or templates. The formation of α-MnO2 with different morphologies, including branched nanorods and nanorods with controllable length, is achieved by controlling the starting concentration of reactants. The morphology and structure of the branched α-MnO2 nanorods are fully characterized and the growth mechanism is proposed based on the experimental observation. The novel structures presented here enrich the nanoscale community of α-MnO2 materials, thus enabling greater potential applications. The electrochemical properties of as-synthesized branched α-MnO2 nanorods are also studied by cyclic voltammetry (CV) and galvanostatic charge/discharge measurement. The branched α-MnO2 nanorod electrode shows a high specific capacitance of 182 F g−1 at a current density of 2 A g−1, with a good rate capability (72.5% at 64 A g−1) and excellent cycling stability.

Hydrothermal synthesis of boron-doped MnO 2 and its decolorization performance

To functionalize MnO2 with foreign ions is one of the commonly used methods to improve the adsorption/oxidation properties of MnO2. Boron-doped MnO2 was prepared by the reaction of MnSO4, KMnO4, and boric acid by a facile hydrothermal method. Boron-MnO2 was characterized by X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction pattern (SAED), and X-ray photo-electron spectroscopy (XPS) techniques. The characterization of XPS and EDX confirms that boron has been doped into MnO2, but the boron dopant has no obvious effect on the crystallization of MnO2 as shown by the results of XRD and Raman characterization. The boron-doped MnO2 nanorods display high performance in the methyl orange degradation with a decolorization degree of 90% in 2 min (5% B-MnO2 dosage, 5mg; methyl orange concentration, 20mg L-1).