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SUMMARYHydrogen permeation across the membrane is unavoidable in proton exchange membrane fuel cells, especially for super‐thin membranes, which lowers the open‐circuit voltage and could even be a safety concern. In this paper, hydrogen permeation across two membranes (25‐um‐thick Nafion® 211 and 18‐um‐thick reinforced composite membrane) are evaluated at various temperatures, relative humidity (RH), and gas pressure differences between the anode and cathode. The results indicate that the hydrogen permeation rate in both membranes increases almost exponentially with temperature and linearly with pressure differences. Compared with RH, the effects of temperature and pressure differences are more crucial to hydrogen permeability. However, the effect of RH on the hydrogen permeation is quite complicated. The permeability exhibits a minimum value at intermediate RH (approximately 40% RH) for both applied membranes. The permeability of Nafion® 211 appears more sensitive to RH than that of reinforced composite membrane at elevated temperature. Copyright © 2013 John Wiley & Sons, Ltd.

The massive exploitation and use of fossil resources have created many negative issues, such as energy shortage and environmental pollution. It prompts us to turn our attention to the development...

Specific salting-in effects that lead to striking substrate selectivity were observed for the hydrolysis of p-nitrophenyl alkanoates 2 (n = 2−16) catalyzed by 4-(dialkylamino)pyridine-functionalized polymer 1 in aqueous Tris buffer solution at pH 8.0 and 30 °C. Macromolecule 1 was found to exhibit clear substrate preference for 2 (n = 6) in 0.05 M aqueous Tris buffer solution, as contrasted with the corresponding reaction in 0.05 M aqueous phosphate or borate buffer solutions where the substrate selectivity is absent. The formation of a reactive catalyst−substrate complex, 1·2, appears to be promoted by the presence of tris(hydroxymethyl)methylammonium ion, an efficient salting-in agent, from the Tris buffer system. The salting-in effect on formation of 1·2 complex is presumed responsible for the substrate specificity. The salting-out effects of sodium chloride on the solvolysis of 2 catalyzed by 1 were also investigated in 1:1 (v/v) methanol−water solution at pH 8.0 and 30 °C. The rate of 1-catalyzed solvolysis of 2 (n = 10−16) was found to vary inversely with NaCl concentration (0−1.0 M). The magnitude of the salting-out effects is dependent on the alkyl chain length in 2 and the concentrations of 1 and NaCl. At 7.5 × 10-5 unit mol L-1 1 and 0−1.0 M NaCl the order of reactivity for 2 (n = 10−16) was n = 10 > 12 > 14 > 16. However, at 5.0 × 10-6 unit mol L-1 1, a revised reactivity order, 2, n = 14 > 12 > 16, was obtained at [NaCl] < 0.15 M. A significant decrease in the substrate preference for 1-catalyzed solvolysis of 2 (n = 10−16) was observed at higher NaCl concentrations. We suggest that the reduced catalytic efficiency and selectivity expressed by 1 in the presence of sodium chloride should be attributed to changes in the morphology and composition of aggregates containing 1 and 2 in aqueous methanol solution that lead to decreased dependence of aggregate formation on the hydrophobicity of the substrate.

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