No abstract

In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the enhancement of the direct thermal to electrical thermoelectric efficiency of n-type PbTe by Na and Cl co-doping.

Three materials containing Ni 2 P, Ni 12 P 5 , and Ni 3 P phases on silica gel with surface area 320 m 2 /g at loadings of 32-37 wt % and the crystal size of Ni x P phases 30, 9, and 13 nm, respectively, were prepared by a combination of impregnation and TPR methods and tested in hydrodesulfurization (HDS) and adsorptive desulfurization (ADS) of diesel fuel. There were established opposite trends in changing the DS efficiency in two processes: The HDS rate constant decreased while the ADS sulfur capacity (breakthrough at 1 ppmw) increased with increasing the Ni to P ratio in Ni x P from 2 to 3. The observed behavior was attributed to the specific features of the densities of states (DOS) obtained from the density functional theory calculations of total and partial DOS for Ni and P in Ni x P phases and revealed in XPS measurements of binding energy of Ni 2p 3/2 -and P 2p-electrons. This attribution was consistent with the analysis of the relative part of d-electrons of Ni participating in bonding with p-electrons of phosphorus in these phases.

Novel approaches for the development of highly efficient thermoelectric materials capable of a direct conversion of heat into electricity, are being constantly investigated. TiNiSn based half-Heusler alloys exhibit a high thermoelectric potential for practical, renewable power generation applications. The main challenge of further enhancement of the thermoelectric efficiency of these alloys lies in the reduction of the associated high lattice thermal conductivity values without adversely affecting the electronic transport properties. The current manuscript theoretically investigates two possible routes for overcoming this limitation in TiNiSn alloys. On the one hand, the influence of nano-grained structure of TiNiSn on the electronic structure of the material is theoretically demonstrated. On the other hand, the potential for thermal conductivity reduction upon increasing the Ni fraction in the intermetallic TiNiSn compound via the formation of metallic TiNi2Sn nanoparticles is also shown. Using the applied approach, a useful route for optimizing both the electronic and thermal properties of half-Heusler TiNiSn, for practical thermoelectric applications, is demonstrated.

We show how the growth mode of a thin metallic film on an insulating substrate can be predicted theoretically by combining thermodynamic considerations with ab initio calculations for ordered metal/insulator interfaces at low coverage. Our approach is illustrated by calculations for Ag film deposited on an MgO substrate. Ab initio calculations predict high mobility of adsorbed Ag atoms on MgO, even at low temperatures, which greatly aids their aggregation.