Márcia Regina Becker

Effect of Ni proportion on the performance of proton exchange membrane fuel cells using PtNi/C electrocatalysts

PtNi/C electrocatalysts were synthesised by borohydride method on functionalised carbon support. Energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and both cyclic and linear voltammetry were employed to characterise the composition, crystalline structure, morphology and catalytic properties of the PtNi/C electrocatalysts. Different Ni proportions in the PtNi/C electrocatalysts were evaluated in the cathode or anode in a H2/air proton exchange membrane fuel cells (PEMFC) by polarisation curves. PtNi particles uniformly dispersed with different proportions of metals obtained. The increase of Ni proportion in the electrocatalyst led to materials with higher mass activity values toward the oxygen reduction reaction and a greater electrochemical-active surface area. PtNi/C electrocatalysts in the cathode presented higher mass activity values at high potential in the PEMFC. The best PEMFC performance was obtained with PtNi 13xa0at.% Ni (cathode) and Pt/C (anode) relative to the Pt/C (cathode and anode) with identical Pt loadings. PtNi/C electrocatalysts in PEMFC may be used as an alternative to Pt/C electrocatalyst.

Refractive index control in bicomponent polymer films for integrated thermo-optical applications

Optical properties of transparent polymer thin films, produced by spin-coating on silicon and constituted of polycarbonate (PC), poly(methyl methacrylate) (PMMA), and PC/PMMA, were investigated with regard to integrated thermo-optical (TO) device applications. Refractive index dependences on wavelength, temperature, and film composition were measured by spectroscopic ellipsometry with a dedicated autocontrolled heater setup, in the ranges of 400 to 800 nm, 25 to 85 °C and 0 to 100 wt % PC, respectively, with determination of Cauchy and Lorentz-Lorenz parameters. Within these intervals, thermomechanical compatibility and pronounced index contrast of around 0.12 between PC and PMMA, as well as their TO coefficients one order of magnitude higher than that of silica, allow convenient tailoring for specific TO requirements. In addition, wide-range fine-tuning of refractive index variation is found to be facilitated by the weak dependence of isothermal dispersion curves and TO coefficients on film composition.

Preparação e Avaliação Térmica e Reológica de Misturas de PEBD/PELBD

LDPE and LLDPE blends were prepared in a single and twin screw mixer, using different kinds and proportions of the LLDPE in order to evaluate their influence on the viscosity and cristallinity of the blends. The blends with LLDPE made with butene or hexene or octene comonomer, prepared in a twin or single screw mixer, did not show significant differences in their curves of viscosity versus shear rate. The addition of LLDPE in the PEBD changes the viscosimetric behavior of the blends especially at higher shear rate. With Differential Scanning Calorimetry we observed that the incorporation of LLDPE in the blends changes the behavior of melting curves due to its different types of crystallites.