Xinbing Zhao

Self-supported hydrothermal synthesized hollow Co3O4 nanowire arrays with high supercapacitor capacitance

We report a facile hydrothermal synthesis method for the large-area growth of self-supported hollow Co3O4 nanowire arrays. The Co3O4 nanowires have an average diameter of 200 nm and grow vertically to the substrates forming aligned nanowire arrays. Interestingly, the as-prepared Co3O4 nanowire arrays combine properties of hollow structure and quasi-single crystallinity. A plausible formation mechanism of hollow Co3O4 nanowire arrays is proposed here. The Co3O4 nanowire arrays grown on the nickel foam are tested as a cathode electrode material for supercapacitor by cyclic voltammograms (CVs) and galvanostatic charge–discharge tests in 1 M KOH. The self-supported hollow Co3O4 nanowire arrays exhibit superior supercapacitor performances with high specific capacitances (599 F g−1 at 2 A g−1 and 439 F g−1 at 40 A g−1) as well as excellent cycle life, making them suitable for high-rate supercapacitor application. The enhanced supercapacitor performances are due to its unique porous structure providing fast ion and electron transfer, large reaction surface area and good strain accommodation.

Bismuth telluride nanotubes and the effects on the thermoelectric properties of nanotube-containing nanocomposites

Nanotubes of quasilayered bismuth telluride compound were prepared by hydrothermal synthesis. Nanotubes have diameters smaller than 100nm and spiral tube-walls. The low-dimensional morphology and hollow structure enable bismuth telluride nanotubes to be a potential thermoelectric material with a high figure of merit due to the efficient phonon blocking effect. The experimental results show that the addition of nanotubes leads to a remarkable decrease in the thermal conductivity with the electrical conductivity much less affected and thus to an increase in the figure of merit of the Bi2Te3-based material.

Freestanding Co3O4 nanowire array for high performance supercapacitors

We report a single-crystalline Co3O4 nanowire array grown on a nickel foam prepared by a hydrothermal synthesis method for supercapacitor application. The Co3O4 nanowires show sharp tips and have an average diameter of 70 nm, and a length up to 25 μm. Impressively, the as-prepared single-crystalline Co3O4 nanowire array exhibits noticeable pseudocapacitive performance with a high capacitance of 754 F g−1 at 2 A g−1 and 610 F g−1 at 40 A g−1 as well as excellent cycling stability. The enhanced supercapacitor performance is due to the unique one-dimensional (1D) architecture, which provides fast diffusion paths for ions and facilitates the electron and ion transfer on the Co3O4/electrolyte interfaces. Moreover, the 1D nanowire array can accommodate the volume expansion and restrain the pulverization and deterioration of Co3O4 during the repeated cycling process, resulting in enhanced cycling stability.

Hierarchically porous NiO film grown by chemical bath deposition via a colloidal crystal template as an electrochemical pseudocapacitor material

Hierarchically porous NiO film has been successfully prepared by chemical bath deposition through monolayer polystyrene sphere template. The film possesses an architecture with a substructure of NiO monolayer hollow-sphere array and a superstructure of porous net-like NiO nanoflakes. The pseudocapacitive behavior of the NiO film is investigated by cyclic voltammograms (CV) and galvanostatic charge-discharge tests in 1 M KOH. The hierarchically porous NiO film exhibits weaker polarization, better cycling performance and higher specific capacitance in comparison with the dense NiO film. The specific capacitance of the porous NiO film is 309 F g−1 at 1 A g−1 and 221 F g−1 at 40 A g−1, respectively, much higher than that of the dense NiO film (121 F g−1 at 1 A g−1 and 99 F g−1 at 40 A g−1). The hierarchically porous architecture is responsible for the enhancement of electrochemical properties.

Syntheses and thermoelectric properties of Bi2Te3∕Sb2Te3 bulk nanocomposites with laminated nanostructure

Nanocomposites with constituent sizes of <50nm are considered as a promising approach to enhance the figure of merit of bulk thermoelectric materials. A simple route involving hydrothermal synthesis and hot pressing was used in this work to prepare Bi2Te3∕Sb2Te3 bulk nanocomposites. It is shown that the composites have a laminated structure composed of Bi2Te3 and Sb2Te3 nanolayers with the thickness varying alternately between 5 and 50nm. The transport measurements indicate that the nanoscale laminated structure improves the thermoelectric performance with the maximal dimensionless figure of merit of 1.47 for the nanocomposite hot pressed from Bi2Te3 and Sb2Te3 nanopowders.

Graphene sheet/porous NiO hybrid film for supercapacitor applications.

We report the preparation of a nickel-foam-supported graphene sheet/porous NiO hybrid film by the combination of electrophoretic deposition and chemical-bath deposition. The obtained graphene-sheet film of about 19 layers was used as the nanoscale substrate for the formation of a highly porous NiO film made up of interconnected NiO flakes with a thickness of 10-20 nm. The graphene sheet/porous NiO hybrid film exhibits excellent pseudocapacitive behavior with pseudocapacitances of 400 and 324 F g(-1) at 2 and 40 A g(-1), respectively, which is higher than those of the porous NiO film (279 and 188 F g(-1) at 2 and 40 A g(-1)). The enhancement of the pseudocapacitive properties is due to reinforcement of the electrochemical activity of the graphene-sheet film.

Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials.

Solid-state thermoelectric technology offers a promising solution for converting waste heat to useful electrical power. Both high operating temperature and high figure of merit zT are desirable for high-efficiency thermoelectric power generation. Here we report a high zT of ∼1.5 at 1,200 K for the p-type FeNbSb heavy-band half-Heusler alloys. High content of heavier Hf dopant simultaneously optimizes the electrical power factor and suppresses thermal conductivity. Both the enhanced point-defect and electron–phonon scatterings contribute to a significant reduction in the lattice thermal conductivity. An eight couple prototype thermoelectric module exhibits a high conversion efficiency of 6.2% and a high power density of 2.2 W cm−2 at a temperature difference of 655 K. These findings highlight the optimization strategy for heavy-band thermoelectric materials and demonstrate a realistic prospect of high-temperature thermoelectric modules based on half-Heusler alloys with low cost, excellent mechanical robustness and stability.

High figures of merit and natural nanostructures in Mg2Si0.4Sn0.6 based thermoelectric materials

Mg2(Si,Sn) compounds have shown great promise for thermoelectric applications due to good thermoelectric properties, nontoxicity, and abundantly available constituent elements. Herein we report on the thermoelectric properties and microstructure of high performance Mg2Si0.4−xSn0.6Sbx (0⩽x⩽0.015) alloys. The state-of-the-art ZT value of ∼1.1 has been attained in the samples with x=0.0075 due to the relatively low thermal conductivity. In light of the simple cubic structure and mostly light constituent elements, the reduction in lattice thermal conductivity has been discussed in connection with a fairly large amount of in situ formed nanostructures in these samples.

Band engineering of high performance p-type FeNbSb based half-Heusler thermoelectric materials for figure of merit zT > 1

We report new p-type FeNb1−xTixSb (0.04 ≤ x ≤ 0.24) half-Heusler thermoelectric materials with a maximum zT of 1.1 at 1100 K, which is twice that of the ZrCoSb half-Heusler alloys. The electrical properties are optimized by a tradeoff between the band effective mass and mobility via a band engineering approach. A high content of Ti up to x = 0.2 optimizes the power factor and reduces the lattice thermal conductivity. In view of abundantly available elements, good stability and high zT, FeNb1−xTixSb alloys could be promising materials for high temperature power generation.

Preferential c-Axis Orientation of Ultrathin SnS2 Nanoplates on Graphene as High-Performance Anode for Li-Ion Batteries

A SnS2/graphene (SnS2/G) hybrid was synthesized by a facile one-step solvothermal route using graphite oxide, sodium sulfide, and SnCl4·5H2O as the starting materials. The formation of SnS2 and the reduction of graphite oxide occur simultaneously. Ultrathin SnS2 nanoplates with a lateral size of 5-10 nm are anchored on graphene nanosheets with a preferential (001) orientation, forming a unique plate-on-sheet structure. The electrochemical tests showed that the nanohybrid exhibits a remarkably enhanced cycling stability and rate capability compared with bare SnS2. The excellent electrochemical properties of SnS2/G could be ascribed to the in situ introduced graphene matrix which offers two-dimensional conductive networks, disperses and immobilizes SnS2 nanoplates, buffers the volume changes during cycling, and directs the growth of SnS2 nanoplates with a favorable orientation.