BRUNO RIBEIRO DE MATOS
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Artigo IPEN-doc 21247 dc Proton conductivity at low-frequency in nafion conductivity spectrum probed by time-resolved SAXS measurements and impedance spectroscopy2015 - MATOS, BRUNO R.; SANTIAGO, ELISABETE I.; REY, JOSE F.Q.; SCURACCHIO, CARLOS H.; MANTOVANI, GERSON L.; HIRANO, LAOS A.; FONSECA, FABIO C.The electric transport properties of Nafion membranes are investigated by impedance spectroscopy (IS) and correlated with small angle X-ray scattering (SAXS). Detailed IS measurements in a wide range of temperature and frequencies (f) allowed separating contributions from different charge carriers in Nafion. At controlled relative humidity and temperature, Nafion IS spectrum exhibits at T > 160 C two distinct frequencyindependent conductivities occurring at high f 106 Hz and low f < 1022 Hz. Such IS measurements were combined with timedependent SAXS measurements under applied dc electric potential, which provided compelling evidence that the low-f dc conductivity is related to the motion of protons via ion-hopping in hydrated Nafion membranes.Artigo IPEN-doc 19558 In situ fabrication of nafion-titanate hybrid electrolytes for high-temperature direct ethanol fuel cell2013 - MATOS, BRUNO R.; ISIDORO, ROBERTA A.; SANTIAGO, ELISABETE I.; LINARDI, MARCELO; FERLAUTO, ANDRE S.; TAVARES, ANA C.; FONSECA, FABIO C.The synthesis and characterization of a novel Nafion-matrix nanocomposite by the in situ conversion of titania particles into titanate nanofilaments such as nanotubes and nanorods are reported. Titania nanoparticles grown inside Nafion hydrophilic domains were converted by a microwave-assisted hydrothermal reaction into the proton conducting titanate nanotubes and nanorods. Detailed characterization by Raman spectroscopy, X-ray diffraction, small-angle X-ray scattering, and transmission electron microscopy evidenced an intimate interaction between titanate nanostructures and the ionomer hydrophilic phase. The favored localization of such high aspect ratio nanofilaments in the ionic phase of Nafion has a marked impact on the properties of the composites. The experimental data showed enhanced mechanical stability at high temperature (∼130 °C) that was correlated to a strong temperature dependence of the proton conductivity in the same temperature range. Such properties contributed to a significant increase of the performance of direct ethanol fuel cells operating at high temperature (∼130 °C) using hybrid Nafion−titanate electrolytes compared to commercial Nafion.