C.J. Song

Enhanced thermoelectric performance of Cu2Se/Bi0.4Sb1.6Te3 nanocomposites at elevated temperatures

Bi2Te3-based thermoelectric materials with large thermoelectric figure of merit, ZT, at elevated temperatures are advantageous in power generation by using the low-grade waste heat. Here, we show that incorporation of small proportion (0.3 vol. %) of nanophase Cu2Se into BiSbTe matrix causes an enhanced high-temperature thermopower due to elevated energy filtering of carriers and inhibition of minority transport besides enhanced phonon blocking from scattering at interfaces, which concurrently result in an ∼20% increase in the power factor and an ∼60% reduction in the lattice thermal conductivity at 488 K. As a result, ZT = 1.6 is achieved at 488 K in the composite system with 0.3 vol. % of Cu2Se. Significantly, its ZT is larger than unit in broad high-temperature range (e.g., ZT = 1.3 at 400 K and ZT = 1.6 at 488 K), which makes this material to be attractive for applications in energy harvesting from the low-grade waste heat.

Enhanced thermoelectric performance of BiSbTe-based composites incorporated with amorphous Si3N4 nanoparticles

Thermoelectric properties of BiSbTe-based composites dispersed with a small amount (<1 vol%) of amorphous Si3N4 (a-Si3N4) nanoparticles (∼25 nm) were investigated in the temperature range from 303 K to 483 K. The results indicate that with a-Si3N4 content increasing, the thermopower (S) of the a-Si3N4/BiSbTe composites increases substantially at T < ∼370 K, due to the decreased carrier concentrations and the enhanced energy-dependent scattering of the carrier at the heterojunction potential. Simultaneously, a-Si3N4 nanodispersion causes ∼20–30% reduction in thermal conductivity (κ) owing to phonon scattering of nanoparticles as well as phase boundaries. As a result, high dimensionless figure of merit (ZT) values of up to 1.20 (∼303 K) and 1.38 (∼383 K) are obtained in Bi0.4Sb1.6Te3 incorporated with only 0.44 vol% a-Si3N4 nanoparticles, demonstrating that the thermoelectric performance of the BiSbTe alloy can be improved effectively through incorporation of a-Si3N4 nanoparticles.

Effect of Graphitic Carbon Nitride on the Electronic and Catalytic Properties of Ru Nanoparticles for Ammonia Synthesis

AbstractGraphitic carbon nitrides were employed to prepare the Ruthenium-based ammonia synthesis catalysts by thermal decomposition of Ru3(CO)12 under N2 or H2 atmosphere. Different pretreatment atmospheres significantly affected the interaction between Ru nanoparticles and the graphitic carbon nitride. The strong metal support interaction enhanced the electronic density transfer from rich-electron π-plane of the support to the Ru nanoparticles. And it further caused the upshift of d-band center of Ru nanoparticles. The upshift of d-band center improved the ability of surface to bond to N2, and consequently the ammonia synthesis activity was enhanced.Graphical AbstractElectron-rich and graphitic carbon nitride enhanced the electron density of Ru nanoparticles. And that caused the upshift of d-band center of Ru nanoparticles. This upshift of d-band center improved the ability of surface to bond to N2, and consequently the ammonia synthesis activity was enhanced.

Improved thermoelectric properties for solution grown Bi2Te3−xSex nanoplatelet composites

We herein report the large-scale synthesis of Bi2Te3−xSex (0.6 ≤ x ≤ 0.75) nanoplatelets through a hydrothermal method and subsequent spark plasma sintering. The effect of selenium alloying and the spark plasma sintering temperature on the thermoelectric properties of the Bi2Te3 nanostructured bulk materials were investigated. The results indicate that compared to samples fabricated in an autoclave, preparing Bi2Te3−xSex in glass beaker with suitable Se alloying and appropriate sintered temperature is an efficient way to reduce the lattice thermal conductivity due to a large number of Bi2TeO5 nanodots with sizes of around 10 nm. Meanwhile, a decrease in electrical resistivity due to increase in carrier mobility and an enhancement of the Seebeck coefficient attribute to decrease in carrier concentration were observed. As a result, the thermoelectric figure-of-merit, ZT, is significantly improved and the maximum value reaches 0.96 for Bi2Te2.25Se0.75 at 490 K.

Electronic metal–support interactions enhance the ammonia synthesis activity over ruthenium supported on Zr-modified CeO2 catalysts

Here we report that the electronic metal–support interaction influences the catalytic activity of ammonia synthesis. This effect produces an upwards shift of the d-band center of Ru nanoparticles. The upward shift of the d-band center of the Ru nanoparticles is considered to enhance the dissociation of the N2 molecule.

Thermoelectric Performance for SnSe Hot-Pressed at Different Temperature

Herein, nanoparticles SnSe are prepared by fusion method together with ball-milling technique and the effect of hot-pressing temperatures on the thermoelectric properties of the dense materials is explored. Due to the optimization of carrier concentration, the peak figure of merit (ZT) value of the compacted material reaches 0.73 for SnSe sample hot-pressed at 400°C and 450°C. The present investigation indicates that the thermoelectric performance of the SnSe compound can be significantly improved by sintering with suitable temperature.

Thermoelectric anisotropy of n-type Bi2Te3−xSex prepared by spark plasma sintering

The anisotropy of the thermoelectric properties of Bi2Te3−xSex (0.3 ≤ x ≤ 0.9) is investigated at temperatures from 300 to 523 K. The results indicate that due to the anisotropic microstructures, the anisotropic resistivity ρ and thermal conductivity κ of Bi2Te3−xSex are obtained. For example, the resistivity ratio ρp/ρn (here subscript n and p denote the directions normal and parallel to the pressing direction, respectively) and thermal conductivity ratio κp/κn for Bi2Te3−xSex are around 1.55–2.25 and 0.53–0.79, respectively. As a result, a highly anisotropic figure of merit (ZT) is obtained. A maximum ZTn of ∼0.7 is obtained in the temperature range of 440–470 K for Bi2Te2.1Se0.9. Moreover, the maximum ZTp for Bi2Te2.6Se0.4 is ∼0.6 in the temperature range from 400 to 470 K.