Shufen Fan

p-type Bi0.4Sb1.6Te3 nanocomposites with enhanced figure of merit

We report enhanced figure of merit, ZT, in p-type Bi0.4Sb1.6Te3 nanocomposites fabricated by a rapid and high throughput method of mixing nanostructured Bi0.4Sb1.6Te3 particles obtained through melt spinning with micronsized particles obtained via solid state reaction. Due to effective scattering of phonons over a wide wavelength spectrum, low thermal conductivity, and moderately good power factor were obtained in the nanocomposites to achieve ZT above 1.5 at room temperature. A maximum ZT of 1.80 was attained at 43 °C for the nanocomposite consisting 40 wt % nanoinclusions. This was a 56% increment over the bulk sample, and the highest ZT reported for Bi2Te3-based materials.

Flexible carbon nanotube papers with improved thermoelectric properties

Although theoretical calculations indicate that the thermoelectric figure of merit, ZT, of carbon nanotubes (CNTs) could reach >2, the experimentally reported ZT values of CNTs are typically in the range of 10−3–10−2, which is not attractive for thermal energy conversion applications. In this work, we report the preparation of flexible CNT bulky paper for thermoelectric applications. The ZT values of the CNT bulky papers could be significantly enhanced by Ar plasma treatment, i.e. increasing it from 0.01 for pristine CNTs to 0.4 for Ar-plasma treated CNTs. The improved thermoelectric properties were mainly due to the greatly increased Seebeck coefficients and a reduction in the thermal conductivities, although the electrical conductivities also decreased. Such an improvement makes the plasma treated CNT bulky papers promising as a new type of thermoelectric material for certain niche applications as they are easily processed, mechanically flexible and durable, and chemically stable.

Rapid fabrication of a novel Sn–Ge alloy: structure–property relationship and its enhanced lithium storage properties

A rapid solidification and high throughput melt spinning process is developed for the fabrication of new Sn–Ge alloys as anodes for high capacity lithium-ion batteries. Compared to pure micron-sized Sn and Ge, the alloy possesses enhanced lithium storage properties. High, reversible and stable capacities of over 1000 mA h g−1 are maintained over 60 cycles at 0.1 C. A good rate capability of 500 mA h g−1 at 5 C is also achieved, making it very attractive for very fast charge/discharge applications. More remarkably, it has a tap density of 2.05 g cm−3 and thus high volumetric capacities of 2050 mA h cm−3 at 0.1 C and 1025 mA h cm−3 at 5 C. The electrode was investigated via ex situ XRD, EXAFS and TEM at various cut-off voltages during the first cycle and after the first cycle to establish the structure–property relationship. The Sn–Ge alloy is observed to undergo a transformation from the crystalline Sn–Ge alloy into phase separated nanocrystalline Sn in an amorphous Ge matrix. The excellent lithium storage properties exhibited by Sn–Ge are attributed to the synergistic effect between the phases and the phase transformation occurred.

n-Type carbon nanotubes/silver telluride nanohybrid buckypaper with a high-thermoelectric figure of merit.

n-Type thermoelectric (TE) materials was made from carbon nanotube (CNT) buckypapers. We used silver telluride (Ag2Te) to achieve electron injection to the CNTs. The TE characterizations on more than 50 samples show that the CNTs/Ag2Te hybrids exhibit negative Seebeck coefficients (e.g., n-type) from -30 to -228 μV/K. Meanwhile, the tunneling coupling between the CNTs and Ag2Te increase the electrical conductance to the range of 10,000-20,000 S/m, which is higher than each single component (CNTs or Ag2Te). These n-type TE buckypapers are flexible and robust with ZT values of 1-2 orders of magnitude higher than previously reproted for CNT-based TE materials. In addition, the preparation of such buckypapers are very simple compared to a tranditonal inorganic process, without the need for hot pressing or spark sintering. These n-type TE buckypapers can provide important components for fabricating CNT-based flexible TE devices with good conversion efficiency.

Preparation and thermoelectric properties of sulfur doped Ag2Te nanoparticles via solvothermal methods

In this work, n-type Ag(2)Te nanoparticles are prepared by a solvothermal approach with uniform and controllable sizes, e.g. 5-15 nm. The usage of dodecanethiol during the synthesis effectively introduces sulfur doping into the sample, which optimizes the charge carrier concentration of the nanoparticles to >1 × 10(20) cm(-3). This allows us to achieve the desired electrical resistivities of <5 × 10(-6)Ω m. It is demonstrated that Ag(2)Te particles prepared by this solvothermal process can exhibit high ZT values, e.g. 15 nm Ag(2)Te nanoparticles with effective sulphur doping show a maximum ZT value of ~0.62 at 550 K.

Aqueous solution synthesis of (Sb, Bi)2(Te, Se)3 nanocrystals with controllable composition and morphology

The introduction of nanostructures has been considered as one of the promising strategies to enhance the thermoelectric performance of bulk materials. In this work, we report a low-cost and facile aqueous solution method to prepare (Sb, Bi)2(Te, Se)3 nanocrystals with controllable composition and morphology by using short ligands containing thiol, acid and amine groups. The control of the morphology of the nanostructures such as nanowires and nanosheets is studied, and both n-type and p-type nanoparticles have been prepared successfully. The results show that the thermal conductivities of these nanocrystals are effectively reduced due to phonon scattering and the thermoelectric performance is affected greatly by the morphology. TE measurements show that the electrical conductivity can be enhanced significantly by using Bi2Te3 nanosheets, and as a result, a maximum thermoelectric figure-of-merit (ZT) of 0.86 is obtained for Bi2Te3 nanosheets at 225 °C.