Hai Su

Controllable synthesis of self-assembly Co3O4 nanoflake microspheres for electrochemical performance.

Tuning the ratios of ethanol to water, self-assembling microspheres composed of Co3O4 nanoflakes are synthesized by the hydrothermal method. The scanning electron microscopy (SEM) images of as-grown samples obviously show that the dispersive multilayered structures gradually change into micro/nanobelts and cubic blocks structures, and then into the desired self-assembled microspheres with increasing ratios of ethanol to water. Also, all the x-ray diffraction (XRD) patterns evidently demonstrate that all obtained Co3O4 has cubic crystal structure. The corresponding synthesis mechanism is discussed in detail. More importantly, the unique self-assembling Co3O4 nanoflake microspheres have excellent electrochemical performance with large specific capacitance, good rate capability and excellent cycling performance, evidently presenting a potential capability of Co3O4 nanoflake microspheres to act as electrode materials for supercapacitors in sustainable power sources.

Composition controlled nickel cobalt sulfide core–shell structures as high capacity and good rate-capability electrodes for hybrid supercapacitors

Herein, we report a type of core–shell structured NixCo3−xS4 (x = 1, 1.5 and 2) through tuning the ratios of Ni to Co by a simple two-step hydrothermal method. Scanning electron microscopy and transmission electron microscopy images of all the Ni–Co sulfides show high porosity and uniform spherical morphology. Moreover, this study demonstrates that controlling the appropriate ratio of Ni to Co in the core–shell structure is crucial for improving the electrochemical performance in a hybrid supercapacitor. Among them, NiCo2S4 with core–shell structure possesses the highest capacity of 155 mA h g−1, whereas as Ni1.5Co1.5S4 shows the excellent rate-capability of up to 80% from 1 to 20 A g−1 and cycling stability, which retains 74% after 2000 cycles. Therefore, tuning the metal element contents provides a feasible approach to achieving the desired high-rate performance and cycling stability of electrode materials in polynary metal sulfides for hybrid supercapacitors.

Facile synthesis of ultrafine cobalt oxide nanoparticles for high-performance supercapacitors

The ultrafine Co3O4 nanoparticles are successfully prepared by a novel solvothermal-precipitation approach which exploits the supernatant liquid of Co3O4 nanoflake micropheres synthesized by solvothermal method before. Interestingly, the water is only employed to obtain the ultrafine nanoparticles in supernatant liquid which was usually thrown away before. The microstructure measurement results of the as-grown samples present the homogeneous disperse ultrafine Co3O4 nanoparticles with the size of around 5-10nm. The corresponding synthesis mechanism of the ultrafine Co3O4 nanoparticles is proposed. More importantly, these ultrafine Co3O4 nanoparticles obtained at 250°C show the highest specific capacitance of 523.0Fg-1 at 0.5Ag-1, 2.6 times that of Co3O4 nanoflake micropheres due to the quantum size effect. Meanwhile, the sample annealed under 350°C possesses the best cycling stability with capacitance retention of 104.9% after 1500 cycles. These results unambiguously demonstrate that this work not only provides a novel, facile, and eco-friendly approach to prepare high-performance Co3O4 nanoparticles electrode materials for supercapacitors but also develops a widely used method for the preparation of other materials on a large scale.

Visible and near-infrared luminescent properties of Pr3+ doped strontium molybdate thin films by a facile polymer-assisted deposition process

Quartz substrate supported Praseodymium (Pr) doped strontium molybdate (SrMoO4) thin films with good uniformity and outstanding fluorescent properties are successfully fabricated via a facile polymer-assisted deposition (PAD) method. In combination with the strong chelating effect of water-soluble polymer on metal cations, the free cations without chelating are effectively ruled out but the remaining chelating metal cations are employed for the highly uniform and accurate stoichiometry luminescent SrMoO4: Pr thin films, layer-by-layer mounting on the common quartz substrates. More importantly, the excellent release of stress from polymer during the growth process of epitaxial thin film can effectively overcome the mismatch between thin film and common quartz substrate and then guarantee the quality of thin film. Under the ultraviolet (UV) light excitation, the samples show high luminescence intensity both in visible and near-infrared (NIR) regions peaked at 646 nm and 1037 nm, mainly ascribing to the transitions of 3P0 → 3F2 and 1G4 → 3H4 of Pr3+ ions. The luminescent properties can be tailored by optimizing the number of spin-coated layers and doping concentrations. The maximum emission occurs at 4 mol% of Pr3+ dopant, and it exhibits an impressive high photoluminescence quantum yield (QY) of up to 86.12%. These results evidently demonstrate the present PAD method is a useful prototype for preparing high performance luminescent thin films even on the cheap quartz substrate.