Enhanced Thermoelectric Performance of CoSb3 Thin Films by Ag and Ti Co-Doping

The Skutterudites CoSb₃ material has been the focus of research for the conversion applications of waste heat to electricity due to its ability to accommodate a large variety of ions in the cages that have been proven effective in improving the thermoelectric performance. Although the co-doped CoSb₃ bulk materials have attracted increasing attention and have been widely studied, co-doped CoSb₃ thin films have been rarely reported. In this work, Ag and Ti were co-doped into CoSb₃ thin films via a facile in situ growth method, and the influence of doping content in the thermoelectric properties was investigated. The results show that all the Ag and Ti co-doped CoSb₃ thin films contain a pure well-crystallized CoSb₃ phase. Compared to the un-doped thin film, the co-doped samples show simultaneous increase in the Seebeck coefficient and the electrical conductivity, leading to a distinctly enhanced power factor. The high power factor value can reach ~0.31 mWm^-1K^-2 at 623 K after appropriate co-doping, which is two times the value of the un-doped thin film we have been obtained. All the results show that the co-doping is efficient in optimizing the performance of the CoSb₃ thin films; the key point is to control the doping element content so as to obtain high thermoelectric properties.

Enantiomer separation of mandelates and their analogs on cyclodextrin derivative chiral stationary phases by capillary GC

Enantiomer separation of mandelates and their analogs, which are important intermediates in asymmetric synthetic and pharmaceutical chemistry, was investigated by capillary gas chromatography using different cyclodextrin derivative chiral stationary phases (CD CSPs). The used cyclodextrin derivatives included permethylated beta-CD (PMBCD), permethylated gamma-CD, heptakis(2,6-di-O-butyl-3-O-butyryl)-beta-CD, heptakis(2,6-di-O-pentyl-3-O-acetyl)-beta-CD and heptakis(2,6-di-O-nonyl-3-O-trifluoroacetyl)-beta-CD (DNTBCD), respectively. Among all the CSPs used, PMBCD and DNTBCD exhibited the broadest and best enantioselectivity for all the racemates investigated. Some thermodynamic parameters were evaluated and an enthalpy-entropy compensation effect was observed in enantiomer separation processes of mandelates and their analogs. Based on thermodynamic data and molecular mechanics calculations, the chiral recognition mechanism of mandelate derivatives on CD CSPs is discussed.

Fabrication and Electrochemical Behavior Investigation of a Polypyrrole/4-Hydroxy-6-methyl-2-mercaptopyrimidine Comodified Gold Electrode

A polypyrrole (PPy)/4-hydroxy-6-methyl-2-mercaptopyrimidine (HMMP) comodified gold electrode was prepared and characterized in the form of PPy/HMMP/Au. The polymerization mechanisms of pyrrole on a bare Au electrode, a dodecanethiol-modified gold electrode, and a HMMP/Au electrode are compared and discussed. With ascorbic acid as a probe, various factors affecting the electrochemical characteristics of the PPy/HMMP/Au electrode are investigated. The catalytic activity for the electrochemical oxidation of l-ascorbic acid was studied in 0.1 mol. L-1 NaCl and 1.0 x 10(-3) mol. L-1 HCl. Both the kinetics of oxidation and the reproducibility of the electrochemical response are enhanced at the comodified electrode compared to that of an unmodified metal electrode or the PPy/Au electrode in determination of ascorbic acid. Copyright 1999 Academic Press.