The specific grain interior and grain boundary conductivities, obtained from impedance spectroscopy and the brick layer model, are reported for BaZr 0.9 Y 0.1 O 3 − δ as a function of p O 2 and temperature. p O 2-dependencies were indicative of dominating ionic and p-type electronic conduction for the grain interior under reducing and oxidizing conditions, respectively, while the grain boundaries showed an additional n-type electronic contribution under reducing conditions. Transmission electron microscopy revealed enrichment of Y in the grain boundary region. These findings indicate the existence of space-charge layers in the grain boundaries. A grain boundary core-space-charge layer model is therefore applied to interpret the data. Using a Mott-Schottky approximation, a Schottky barrier height of 0.5-0.6 V and an effective grain boundary width of 8-10 nm (= 2× space-charge layer thickness) is obtained at 250°C in wet oxygen. Finite-element modelling of the complex impedance over a grain boundary with a space-charge layer depletion of protons yields a distorted semicircle as observed in the impedance spectra.

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An investigation of the kinetics of the emulsion polymerization of vinyl chloride has been performed. The effect on the rate of reaction of such variables as concentration of initiator (K2S2O8), amount and type of emulsifier and number of latex particles has been investigated at 50°C. The order of reaction with respect to initiator was found to be 0.5. The rate of reaction was found to increase with increasing conversion. The number of latex particles was found to be constant during the polymerization, between 10 and 90% conversion, and also found to be independent of the concentration of initiator. The order of reaction with respect to the number of particles was found to increase from 0.05 to 0.15 in the range investigated (Nw = 1016‐1019 per liter H2O). The order decreases slightly with increasing conversion. A mechanism involving a rapid desorption and reabsorption of radicals in the latex particles is proposed. A marked increase in rate was observed at about 70–80% conversion. A closer investigation of this phenomenon was performed by a continuous addition of vinyl chloride at a pressure below the saturation pressure of vinyl chloride corresponding to the reaction temperature. It appeared that under such conditions reaction rates of about twice those of the ordinary runs might be obtained. No change in the number of particles was observed, either during the polymerization or compared to the ordinary run at the same concentrations of emulsifier and initiator. The effect of the degree of reduction in the pressure of vinyl chloride was also investigated. It was found that the rate of reaction passed through a maximum at a pressure of about 6.75 atm, as compared to 7.75 atm in an ordinary run (Saturation pressure of vinyl chloride at 50°C).

and Ivo Vankelecom, The performance of affordable and stable cellulose-based poly-ionic membranes in CO 2 /N 2 and CO 2 /CH 4 gas separation,

h i g h l i g h t s g r a p h i c a l a b s t r a c t A new technique, that introduces micrometer sized pores in the nanoporous catalyst layer, is tested. The technique uses monodisperse polystyrene particles as pore formers. Macropores in the nanoporous layer improves the polymer electrolyte fuel cell performance. Results are obtained for catalyst loading which are twice the US DOE target for 2020. a b s t r a c tWe show experimentally for the first time that the introduction of macro-pores in the nanoporous catalyst layer of a polymer electrolyte membrane fuel cell can improve its performance. We have achieved a Pt utilization of about 0.23 mg W À1 at 0.6 V which is twice the value of the DOE target for 2020, and three times (0.60 mg W À1 ) smaller than the value of a fully nanoporous reference layer at a catalyst loading of 0.11 mg cm À2 . In this work, monodispersed polystyrene particles with diameters of 0.5 and 1 mm were used as pore formers. Cathode catalyst layers with macroporous volume fractions between 0 and 0.58 were investigated. Maximum performance was observed for fuel cells with a macroporous volume fraction of about 0.52 for a 1 mm thick catalyst layer. The results, which were obtained for the cathode layer, support earlier theoretical predictions that gas access to and water escape from the catalyst can be facilitated by introduction of macropores in the nanoporous layer.