The influence of convection and interfacial-reaction resistance on the response of microsensors, including the effects of: (i) fluid flow rates; (ii) reactant (to be sensed) concentration and diffusion coefficient; (iii) fluid conduit and microsensor size; and (iv) sensor potential and interfacial-reaction resistance, are clarified. For steady-state convective diffusion to a niicrodisk sensor, it is shown that sensor response is a monotonic function of two dimensionless groups: the Péclet number Pe, which characterizes the magnitude of convective transport relative to that of diffusion, and the group tan (8), which provides a measure of diffusive-transport resistance relative to that of the interfacial charge-transfer reaction. A singular-perturbation solution provides the sensor response vs. Pe and 0 for small Pe, corresponding to slow fluid flows and small disks, and numerical calculations extend the analysis to higher Pe values. The analysis suggests a method for increasing the signal-to-noise ratio through altering the sensor bias potential.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 136.167.3.36 Downloaded on 2014-11-02 to IP

We have previously reported a preparation process for the catalyst layer of polymer electrolyte fuel cells (PEFCs) using perfluorosulfonate ionomer (PFSI) colloid. In this paper we report recent improvements in this method of preparation. In the present method, a carbon-supported platinum catalyst (Pt-C) was mixed with poor solvent for PFSI, and PFSI solution was added to this mixture. The colloidal PFSI formed was immediately adsorbed on Pt-C without coagulation. As a result, the reaction area was increased, the internal resistance was decreased, and the gaseous reactants were more readily supplied to the reaction area. We also studied the influence of the carbon support on the microstructure of the catalyst layer. We have found that the performance of a PEFC prepared by this process with optimum carbon support and with very low platinum loading (0.1 mg/cm2) was superior to that prepared by our previous process with conventional carbon support and with a 0.5 mg/cm2 platinum loading.

Although several types of chiral hypervalent iodine reagents have been used for asymmetric induction, all of them have needed more than a stoichiometric amount of chiral reagents and have shown low enantioselectivities. The described new catalytic asymmetric oxidation using a hypervalent iodine(V) reagent, iodoxybenzene (PhIO(2)), in a cationic reversed micellar system provides the first example of a catalytic asymmetric oxidation of sulfides to sulfoxides in high chemical yield with moderate to good enantioselectivity without the use of any transition-metal catalysts. The solubilization and activation of PhIO(2) by adding catalytic amounts of both cetyltrimethylammonium bromide (CTAB) and a chiral tartaric acid derivative were found to be indispensable for the enhancement of chemical and optical yields.

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