Zhongqi Shi

Enhanced thermal conductivity of polymer composites filled with three-dimensional brushlike AlN nanowhiskers

The thermal conductivity of polymer composites was improved by loading three-dimensional (3D) brushlike AlN nanowhiskers fillers synthesized by simple combustion method. Through filling 47 vol % of the synthesized AlN nanowhiskers, the thermal conductivity of the composite was significantly increased to 4.2 W m−1 K−1, which was 2.3 times higher than that of the composite filled with the same content of commercial AlN equiaxed particles. According to Agari model analysis and microstructure observation, the thermal conductivity enhancement can be ascribed to the 3D brushlike AlN nanowhiskers promoted the formation of a more effect percolating network in the matrix with lower thermal resistance.

CoSe2 necklace-like nanowires supported by carbon fiber paper: a 3D integrated electrode for the hydrogen evolution reaction

Pyrite-type CoSe2 necklace-like nanowires (NWs) were successfully grown on carbon fiber paper (CFP) and proven to be an efficient electrocatalyst towards the hydrogen evolution reaction (HER). By combining the use of mesoporous CFP and the nano-structuring of the electrocatalyst, the highly active CoSe2 necklace-like NWs on CFP only need the modest overpotentials of 188 and 199 mV to afford the current densities of 50 and 100 mA cm−2, respectively. A small Tafel slope of 34 mV dec−1 and a charge transfer resistance of 7.05 Ω illustrate the prominent electrocatalytic performance. After continual electrolysis for 20 h or conducting cycling for 5000 times, the high activity of CoSe2 NWs toward the HER is still perfectly preserved. The outstanding electrocatalytic performance and stability make the CoSe2 necklace-like NWs on CFP a promising earth-abundant electrocatalyst for the HER and other renewable energy applications.

Nanowires as Building Blocks to Fabricate Flexible Thermoelectric Fabric: The Case of Copper Telluride Nanowires

A general approach to fabricate nanowires based inorganic/organic composite flexible thermoelectric fabric using a simple and efficacious five-step vacuum filtration process is proposed. As an excellent example, the performance of freestanding flexible thermoelectric thin film using copper telluride nanowires/polyvinylidene fluoride (Cu1.75Te NWs/PVDF = 2:1) as building block is demonstrated. By burying the Cu1.75Te NWs into the PVDF polymer agent, the flexible fabric exhibits room-temperature Seebeck coefficient and electric conductivity of 9.6 μV/K and 2490 S/cm, respectively, resulting in a power factor of 23 μW/(mK(2)) that is comparable to the bulk counterpart. Furthermore, this NW-based flexible fabric can endure hundreds of cycles of bending tests without significant performance degradation.

Morphology-Controllable Synthesis of Cobalt Telluride Branched Nanostructures on Carbon Fiber Paper as Electrocatalysts for Hydrogen Evolution Reaction

Cobalt telluride branched nanostructures on carbon fiber paper (CFP) with two different morphologies were synthesized via solution-based conversion reaction. Both the CoTe2 with nanodendrite and CoTe with nanosheet morphologies on the CoTe2 nanotube (CoTe2 NDs/CoTe2 NTs and CoTe NSs/CoTe2 NTs) supported by CFP exhibit high activities toward hydrogen evolution reaction (HER). Particularly, the CoTe NSs/CoTe2 NTs only require an overpotential of 230.0 mV to deliver the current density of 100 mA cm(-2) in acid solution. After cycling for 5000 cycles or 20 h continual electrolysis, only a small performance loss is observed.

Environmentally benign synthesis of high-quality, band gap-tunable, homogeneous Te/Se alloyed nanowires

Ultrathin trigonal Te/Se alloyed nanowires with a tunable composition and band gap were fabricated using a nonhazardous reducing agent, ascorbic acid. The as-synthesized nanowires displayed a tunable direct band gap (3.39 to 3.78 eV) and indirect band gap (1.99 eV to 2.93 eV).

Ultralight, Recoverable, and High-Temperature-Resistant SiC Nanowire Aerogel

Ultralight ceramic aerogels with the property combination of recoverable compressibility and excellent high-temperature stability are attractive for use in harsh environments. However, conventional ceramic aerogels are usually constructed by oxide ceramic nanoparticles, and their practical applications have always been limited by the brittle nature of ceramics and volume shrinkage at high temperature. Silicon carbide (SiC) nanowire offers the integrated properties of elasticity and flexibility of one-dimensional (1D) nanomaterials and superior high-temperature thermal and chemical stability of SiC ceramics, which makes it a promising building block for compressible ceramic nanowire aerogels (NWAs). Here, we report the fabrication and properties of a highly porous three-dimensional (3D) SiC NWA assembled by a large number of interweaving 3C-SiC nanowires of 20-50 nm diameter and tens to hundreds of micrometers in length. The SiC NWA possesses ultralow density (∼5 mg cm-3), excellent mechanical properties of large recoverable compression strain (>70%) and fatigue resistance, refractory property, oxidation and high-temperature resistance, and thermal insulating property (0.026 W m-1 K-1 at room temperature in N2). When used as absorbents, the SiC NWAs exhibit an adsorption selectivity of low-viscosity organic solvents with high absorption capacity (130-237 g g-1). The successful fabrication of such an attractive material may provide promising perspectives to the design and fabrication of other compressible and multifunctional ceramic NWAs.

Scalable solution-based synthesis of component-controllable ultrathin PbTe1−xSex nanowires with high n-type thermoelectric performance

As an important candidate for thermoelectric (TE) applications, the preparation of PbTe-based one-dimensional nanostructures with controllable components and properties remains a challenge. Herein, we report a new approach for the scalable solution-based synthesis of component-controllable ultrathin Se-doped PbTe (PbTe1−xSex, 0 ≤ x ≤ 0.5) single-phase ternary nanowires (NWs), which serve as building blocks for fabricating bulk nanostructured TE materials. Unexpectedly, Se dopant stabilized the NWs and favored the formation of a unique long-range-ordered nanonetwork structure inside the bulk, which led to a peak figure of merit (ZT) of 1.1 at 643 K and an average ZT of 0.9 in the range of 300–673 K, which was one of the highest values reported for the n-type nanostructured PbTe-based materials.

Microstructure and Tensile Behavior of Ni-Base Metal-Intermetallic Laminate Composites Prepared by Plasma Activated Sintering

Abstract Ni-base metal-intermetallic laminate (MIL) composites were obtained from in-situ combustion reaction between the Ni and Al foils by a plasma activated sintering (PAS). Microstructural observation reveals that the laminates consist of alternate residual Ni layers and reacted layers which can be further divided into multiple layers of Ni-aluminides. The compositional gradient series of these intermetallic phases change in a stepwise fashion from Al-rich phases to Ni-rich phases with the increasing of the treatment temperature. Accordingly, the tensile strength of the composite increases steadily with the increase of temperature. The composites fabricated at 1473 K have the highest tensile strength and elongation. The fractographies of the tensile samples indicate that the failure of the composites treated at lower temperatures (1073 K and 1173 K) result from the interaction between the transversal cracks in the intermetallic layers and the shear bands in the Ni layers. When the treatment temperature increases, a transition from multiple cracking to a single cracking of the intermetallic layers can be observed.

Tuning the structures and electron transport properties of ultrathin Cu nanowires by size and bending stress using DFT and DFTB methods

The electron transport properties of ultrathin Cu nanowires (NWs) with diameters of 0.2–1.0 nm under different bending stresses are reported for potential future application in flexible displays and flexible solar cells. Density functional theory (DFT) and density-functional-based tight-binding (DFTB) approaches have been combined to systematically discover the ballistic transport and diffusive transport of ultrathin Cu NWs at the nanoscale. Our DFT calculations show that with an increase of bending stress (f), the structures of both nonhelical and helical wires become disordered, then exhibit a phase transition and eventually collapse. Therefore, the quantum conduction (G) values are reduced. In addition, as the size of the nanowires increases, the maximum bearable bending stress (fc) reduces. fc of a helical atomic strand is decided by its diameter, while fc of a nonhelical atomic strand is decided by the area of the cross section. Our DFTB calculations reveal that the intermediary atoms are the most important for forming the loop between two electrodes and implementing diffusion transport. Among the seven structures, 6-1b exhibits the best properties, after comprehensively considering the results of quantum transport, diffusive transport and collapse-resistance.

Synthesis, crystal structure and photoluminescence of novel blue-emitting Eu2+-doped (SiC)x–(AlN)1−x phosphors by a nitriding combustion reaction

Novel blue-emitting phosphors with the chemical composition of (SiC)x–(AlN)1−x:yEu2+ (x = 0.06–0.50, y = 0.001–0.01) were synthesized by a nitriding combustion reaction route, and the crystal structure, luminescence properties and thermal stability of the (SiC)x–(AlN)1−x:yEu2+ phosphors were investigated by theoretical and experimental approaches. First-principles calculation results prove that the solid solution of SiC with AlN promotes the doping of Eu2+ ions into the (SiC)x–(AlN)1−x host lattice, and Eu2+ ions tend to occupy Al sites of the host. The synthesized (SiC)x–(AlN)1−x:yEu2+ phosphors absorb light in the region of 250–425 nm and show a single and symmetric broadband emission centered at about 470 nm due to the 4f65d–4f7 transitions of Eu2+. The luminescence intensity increases with the SiC content and reaches its maximum at x = 0.20. The critical quenching concentration of Eu2+ in the (SiC)0.20–(AlN)0.80:yEu2+ phosphor is about y = 0.006. The composition-optimized (SiC)0.20–(AlN)0.80:0.006Eu2+ phosphor shows a small thermal quenching, retaining the luminance of 91.1% at 150 °C. The CIE coordinates were measured as (0.135, 0.167) with high color purity. The above results indicate that (SiC)x–(AlN)1−x:yEu2+ is a promising candidate as a blue-emitting ultraviolet convertible phosphor for white LEDs, and the combustion reaction route is expected to be applicable to the synthesis of other kinds of nitride phosphors.