Influence of electrode structure on the performance of a direct methanol fuel cell

Direct methanol fuel cells (DMFCs) consisting of multi-layer electrodes provide higher performance than those with the traditional electrode. The new electrode structure includes a hydrophilic thin film and a traditional catalyst layer. A decal transfer method was used to apply the thin film to the Nafion(R) membrane. Results show that the performance of a cell with the hydrophilic thin film is obviously enhanced. A cell with the optimal thin film electrode structure operating at I M CH3OH, 2 atm oxygen and 90degreesC yields a current density of 100 mA/cm(2) at 0.53 V cell voltage. The peak power density is 120 mW/cm(2). The performance stability of a cell in a short-term life operation was also increased when the hydrophilic thin film was employed. (C) 2002 Elsevier Science B.V. All rights reserved.

Direct synthesis and characterization of titanium-substituted mesoporous molecular sieve SBA-15

Ti-substituted mesoporous SBA-15 (Ti-SBA-15) materials have been synthesized by using a new approach in which the hydrolysis of the silicon precursor (tetramethoxysilane, TMOS) is accelerated by fluoride. These materials were characterized by powder X-ray diffraction patterns (XRD), X-ray fluorescence spectroscopy (Y-RF), N-2 sorption isotherms, diffuse-reflectance UV-visible (UV-vis) and UV-Raman spectroscopy, Si-29 MAS NMR, and the catalytic epoxidation reaction of styrene. Experiments show that Ti-SBA-15 samples of high quality can be obtained under the following conditions: F/Si greater than or equal to 0.03 (molar ratio), pH less than or equal to 1.0, aging temperature less than or equal to 80 degreesC, and Ti/Si less than or equal to 0.01. It was found that the hydrolysis rate of TMOS was remarkably accelerated by fluoride, which was suggested to play the main role in the formation of Ti-SBA-15 materials of high quality. There is no stoichiometric incorporation of Ti, and the Ti contents that are obtained are quite low in the case of the approach that is proposed. The calcined Ti-SBA-15 materials show highly catalytic activity in the epoxidation of styrene.

Direct observation of subsurface oxygen on the defects of Pd(100)

Oxygen adsorption and desorption on a Pd(100) surface with a mesoscopic defect were studied by photoemission electron microscopy (PEEM). The defect surface, with an area of approximately 200 x 60 mu m(2), behaved differently from the perfect Pd(100) surface towards the adsorption of oxygen. When saturated, both surface oxygen and subsurface oxygen coexisted on the defect surface, whereas only surface oxygen was present on the Pd(100) surface. Upon heating, subsurface oxygen diffused back to the surface and desorbed with surface oxygen at the same time. The difference in oxygen adsorption ability between the defect surface and the perfect Pd(100) surface can be attributed to different structures of these two surfaces. (C) 1999 Elsevier Science B.V. All rights reserved.

Direct enantiomer separation of 2-phenylcyclopropanecarboxylate esters on cyclodextrin derivatives stationary phases in GC

Direct enantiomeric separation of all four optical isomers of 2-phenylcyclopropane carboxylate ester was first achieved on each of the three different beta-cyciodextrin chiral stationary phases (CSPs) in GC. Using these CSPs, enantiomeric excess of the products of enantioselective cyclopropanation can be determined directly, conveniently and fast.