JAQUELINE DE SOUZA DA SILVA
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Resumo IPEN-doc 23728 Structure and transport properties of annealed nafion membranes2016 - MATOS, BRUNO R.; SILVA, JAQUELINE de S. da; FONSECA, FABIO C.The relationship between electrical properties and the structural features of annealed Nafion samples was investigated by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and impedance spectroscopy. Understanding of the observed effects on the proton conductivity due to annealing at controlled humidity at high temperature is crucial for improving the polymer electrolyte fuel cell (PEFC) at high operating temperatures (T > 100 °C) [1]. The experimental results reveal that membranes submitted to a heat treatment in the 100 – 200 °C temperature interval at low relative humidity (RH), display higher crystallinity and irreversibly shrinking of the ionic domains. However, the electrical properties of the polymer matrix were mostly affected by the irreversible destabilization of the ionic phase. The increase in crystallinity and shrinking of the hydrophilic domains reduce the ionomer conductivity. These features were reflected in the polymer electrolyte fuel cell (PEFC) tests in which the measured performance was lower for Nafion samples annealed at high T compared to pristine membranes. Such results are relevant for the preparation of membrane electrode assemblies as well as for the development of highperformance ionomer membranes.Resumo IPEN-doc 23626 Properties and defc tests of nafion added functionalized titanate nanotubes prepared by extrusion2016 - MATOS, B.R.; GOULART, C.A.; ISIDORO, R.A.; SILVA, J.S. da; SANTIAGO, E.I.; FONSECA, F.C.; TAVARES, A.C.Composite electrolyte membranes based on the incorporation of a second inorganic phase into ionomer matrices such as Nafion revealed to possess enhanced properties such as increased mechanical resistance and reduced permeability of solvents. It has been reported that surface functionalized titanate nanotubes (H2Ti3O7.nH2O) display a proton conductivity of ~ 10-2 Scm-1, which is attractive for the use of such composites in direct ethanol fuel cells (DEFC). Herein, composite membranes based on the addition of sulfonic acid groups functionalized titanate nanotubes into Nafion matrix were prepared by grafting followed by extrusion. These membranes were characterized by infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), acid-base titration, proton conductivity measurements and DEFC tests. FTIR measurements confirmed both the grafting of the titanate nanotubes. BET measurements showed that the functionalized titanate nanotubes possess a high surface specific area. Acid-base titration evidenced that additional sulfonic acid groups are present in the composite membranes compared to the pristine ionomer. The conductivity measurements show that the increase in the titanate nanotube volume fraction into the ionomers has not resulted in a decrease of the proton conductivity. The results show that the addition of functionalized titanate nanotubes into Nafion polymer matrix resulted in an improvement of the electric transport properties, reduction of the fuel crossover and, consequently, a higher DEFC performance for the composites were observed with respect to the pristine Nafion.