Zhenghua Wang

Homogeneous core–shell NiCo2S4 nanostructures supported on nickel foam for supercapacitors

In this study, we report the fabrication of NiCo2S4 with a homogeneous core–shell nanostructure in which NiCo2S4 nanotubes are wrapped by NiCo2S4 nanosheets. The core–shell structured NiCo2S4 was in situ grown on nickel foam and can be directly applied as a supercapacitor electrode. Electrochemical tests demonstrate that the NiCo2S4 electrode achieved a high specific capacitance of 1948 mF cm−2 at a current density of 1 mA cm−2, a good rate capability, and an excellent cycling stability. The outstanding performance of the NiCo2S4 electrode can be attributed to its core–shell architecture with good mechanical and electrical contact and rich redox reactions, as well as high transport rate for both electrolyte ions and electrons. By applying NiCo2S4 as the positive electrode and porous carbon as the negative electrode, an asymmetric supercapacitor device was fabricated and it exhibited an excellent electrochemical performance. These results demonstrate that the homogeneous core–shell NiCo2S4 nanostructure is promising for supercapacitor applications.

Co9S8 nanotubes synthesized on the basis of nanoscale Kirkendall effect and their magnetic and electrochemical properties

Polycrystalline Co9S8 nanotubes were successfully fabricated by using Co(CO3)0.35Cl0.20(OH)1.10 nanorod bunches as sacrificial hard templates through a hydrothermal route. The samples were characterized by means of XRD, XPS, SEM and TEM. The Co9S8 nanotubes were formed due to the nanoscale Kirkendall effect, which can be explained by the difference in diffusion rates between the cobalt source and the sulfur ion. Magnetic measurements indicate that the Co9S8 nanotubes show a paramagnetic property instead of a ferromagnetic property, which can be attributed to the tiny sizes of the component nanoparticles. The electrochemical properties of the Co9S8 nanotubes demonstrate that they deliver a large discharge capacity, which might find possible applications as an electrode material in lithium batteries.

Photocatalytic synthesis of M/Cu2O (M = Ag, Au) heterogeneous nanocrystals and their photocatalytic properties

M/Cu2O (M = Ag, Au) heterogeneous nanocrystals are successfully prepared by depositing noble metal nanoparticles onto the surfaces of Cu2O octahedral nanocrystals through a simple photocatalytic process. The samples are characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). The influence of the light source and solution temperature on the deposition of noble metal (taking Ag as an example) nanoparticles has been studied. The experimental results show that visible light is more favorable for the deposition of Ag nanoparticles onto Cu2O nanocrystals, and a solution temperature of more than 30 °C can prevent the erosion of Cu2O. The photocatalytic properties of the prepared M/Cu2O heterogeneous nanocrystals are studied, showing enhanced photocatalytic activities.

Synthesis of polycrystalline cobalt selenide nanotubes and their catalytic and capacitive behaviors

Polycrystalline Co0.85Se nanotubes are successfully prepared by using Co(CO3)0.35Cl0.20(OH)1.10 nanorods as precursor through a solvothermal process. The as-prepared Co0.85Se nanotubes show efficient catalytic performance for decomposition of hydrazine hydrate at room temperature. The catalysts can be repeatedly used and their repeatability is also excellent. The Co0.85Se nanotubes can also be applied as supercapacitor electrode materials. Galvanostatic charge–discharge measurements show that the Co0.85Se nanotube electrode has a specific capacitance of 238 F g−1 at a current density of 1 A g−1 after 100 cycles of activation, and retaining 90.3% of the capacitance after the next 1900 cycles.

Synthesis of Core-Shell @@ Microspheres and Their Application as Recyclable Photocatalysts

We report the fabrication of core-shell Fe3O4@SiO2@TiO2 microspheres through a wet-chemical approach. The Fe3O4@SiO2@TiO2 microspheres possess both ferromagnetic and photocatalytic properties. The TiO2 nanoparticles on the surfaces of microspheres can degrade organic dyes under the illumination of UV light. Furthermore, the microspheres are easily separated from the solution after the photocatalytic process due to the ferromagnetic Fe3O4 core. The photocatalysts can be recycled for further use with slightly lower photocatalytic efficiency.

Hierarchical NiCo2O4@NiCo2S4 Nanocomposite on Ni Foam as an Electrode for Hybrid Supercapacitors

In this work, NiCo2O4@NiCo2S4 nanocomposite with a hierarchical structure is prepared by a multistep process. First, NiCo2O4 nanowires array on Ni foam is prepared by a hydrothermal and a subsequent calcination process. Then, the NiCo2O4 nanowires array is converted to NiCo2O4@NiCo2S4 nanocomposite through a vapor-phase hydrothermal process. The NiCo2O4@NiCo2S4/Ni foam electrode exhibits a specific capacitance of 1872 F g–1 at 1 A g–1, a capacitance retention of 70.5% at 10 A g–1, and a retention ratio of 65% after 4000 charge–discharge cycles. The capacitance of NiCo2O4@NiCo2S4 nanocomposite is much higher than that of the NiCo2O4 nanowires array. The excellent electrochemical capacitive performances of the NiCo2O4@NiCo2S4 nanocomposite can be attributed to the hierarchical nanostructure, which can provide large surface areas and short diffusion pathways for electrons and ions. By using the NiCo2O4@NiCo2S4/Ni foam as the positive electrode and activated carbon/Ni foam as the negative electrode, a hybrid supercapacitor device is fabricated. The device achieves an energy density of 35.6 W h kg–1 and a power density of 1.5 kW kg–1 at 2 A g–1.