Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

http://science.sciencemag.org/content/sci/297/5582/787.full.pdf

Carbon Nanotubes--the Route Toward Applications

Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then-despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of approximately 2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.

Thin-film thermoelectric devices with high room-temperature figures of merit

[Liu, Chang; Li, Feng; Ma, Lai-Peng; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

Advanced Materials for Energy Storage

Metal hydride materials for solid hydrogen storage: a review

Increased attention is being focused on metal-organic frameworks as candidates for hydrogen storage materials. This is a result of their many favorable attributes, such as high porosity, reproducible and facile syntheses, amenability to scale-up, and chemical modification for targeting desired properties. A discussion of several strategies aimed at improving hydrogen uptake in these materials is presented. These strategies include the optimization of pore size and adsorption energy by linker modification, impregnation, catenation, and the inclusion of open metal sites and lighter metals.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.200462786

Strategies for hydrogen storage in metal--organic frameworks.

We have studied the transport properties in a family of pure and doped intermetallics of the form MNiSi (M=Zr, Hf), the structures known as the half-Heusler alloys. We have shown that the transport is very sensitive to structural arrangements of the constituent atoms, and this can be manipulated by annealing, isostructural alloying, and doping. The unusual transport properties are viewed in the context of a semimetal-semiconductor transition that in pure alloys sets in near 150 K. Doping with indium can shift the transition upward towards 200 K. The high-temperature transport is dominated by the presence of heavy electrons that are responsible for surprisingly large values of thermopower. Minute amount of antimony (n-type doping) have a spectacular influence on the nature of transport and drive the electrical resistivity and Hall effect to be metal-like at all temperatures. Sb-doped alloys display very high thermoelectric power factors, but the thermal conductivity is still too high to make the material a prospective thermoelectric.

Transport properties of pure and doped mnisn (m=zr, hf)

CeFe4Sb12 is a member of a class of advanced thermoelectric materials. In order to evaluate this material’s potential for such applications, we have measured a variety of its properties at low temperature, including thermal conductivity, thermoelectric power, electrical resistivity, Hall coefficient, and magnetic susceptibility.

Low temperature properties of the filled skutterudite CeFe4Sb12

Hydrogen storage capacity of carbon nanotubes, filaments, and vapor-grown fibers

We report on the effects of partial substitution of nickel by palladium on the thermoelectric properties of ZrNiSn-based half-Heusler compounds. It is shown that the substitution of palladium for nickel results in a significant, beneficial reduction of the thermal conductivity. The Seebeck coefficient also decreases, but only by a small amount. In the Hf0.5Zr0.5Ni0.8Pd0.2Sn0.99Sb0.01 compound, a power factor of 22.1 μW K−2 cm−1 and a thermal conductivity as low as 4.5 W/m K are measured at room temperature. The dimensionless figure of merit ZT increases with increasing temperature and reaches a maximum value of 0.7 at about 800 K.

/pdf/effects-of-partial-substitution-of-ni-by-pd-on-the-1b68swan6z.pdf

Effects of partial substitution of Ni by Pd on the thermoelectric properties of ZrNiSn-based half-Heusler compounds

We present a model calculation of the lattice thermal conductivity of ZrNiSn-based half-Heusler thermoelectric compounds for temperatures where phonon scattering is dominated by Umklapp and point defect scattering. The difference in mass between impurity and host atoms dominates point defect scattering for alloying Hf on the Zr sublattice, whereas differences in size and interatomic coupling forces between impurity and host atoms dominate point defect scattering for alloying Pd on the Ni sublattice. Because Pt is heavier and larger than Pd, we predict that Pt will further reduce lattice thermal conductivity when alloyed on the Ni sublattice of these half-Heusler compounds.

Gregory P. Meisner

Papers

Transport properties of pure and doped mnisn (m=zr, hf)

Low temperature properties of the filled skutterudite CeFe4Sb12

Hydrogen storage capacity of carbon nanotubes, filaments, and vapor-grown fibers

Effects of partial substitution of Ni by Pd on the thermoelectric properties of ZrNiSn-based half-Heusler compounds

Strain field fluctuation effects on lattice thermal conductivity of ZrNiSn-based thermoelectric compounds