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Self-supported mesoporous Pt nanospheres are prepared by the templated method for the electrocatalytic oxygen reduction reaction (ORR). Single-crystal-like MCM-48 nanospheres, synthesized via a new and simple route in a dilute and alkaline solution of benzylcetyldimethylammonium chloride, are applied as the hard template. A facile process of molten salt impregnation followed by hydrogen reduction is developed to replicate both the mesostructure and morphology of the hard template and to form mesoporous Pt nanospheres. The high-surface-area mesoporous Pt nanospheres are thermally stable in air up to 300 °C without showing significant metal sintering. Electrocatalytic studies reveal that mesoporous Pt nanospheres have a large fraction of {110} facets and exhibit high activity for the ORR. The excellent electrocatalytic performance may be mainly attributed to the facet-dependent ORR activities as well as the presence of 3D interconnected mesopores to facilitate mass transport.

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ABSTRACT:The effects of three different variables (initiator concentration, polarity of the solvent and reaction temperature) on the rate of dispersion polymerization of styrene in alcohols have been investigated. It was found that the rate of polymerization increases with the initiator (AIBN) concentration at the 0% conversion level and becomes independent of it at higher monomer conversions. More significant was the result that the rate was also found to increase with solvent polarity. This is consistent with thermodynamic equilibrium calculations which account for the partitioning behavior of monomer and solvent in both the solution and the particle phases. The results further suggest the existence of two different kinetic regions: one at low conversions, where the reaction takes place primarily in the solution phase, and one at high conversions, where the reaction takes place primarily in the particle phase.