JAQUELINE DE SOUZA DA SILVA
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Resumo IPEN-doc 25425 Electrostatic interactions of Ionomer Films as Probed by Variable Temperature Synchrotron Infrared Spectroscopy2018 - SILVA, J.S. da; MATOS, B.R.; SCHADE, U.; PUSKAR, L.; FONSECA, F.C.The state of the art polymer electrolyte of Proton Exchange Membrane Fuel Cells (PEM), Nafion®, has poor mechanical and electrical properties at T > 100 °C. Specifically, long-term operation leads to irreversible performance losses that are related to an irreversible modification of the ionomer morphology above the temperature of alpha-transition (Talpha ~ 110 °C). Previous characterizations showed that the alpha-transition is dependent on the different states of covalent and ionic interactions among sulfonic acid groups, such as: ionic repulsions among RSO3-, dipolar attractions among RSO3H dipoles, hydrogen bonding of sulfonic groups with bulk and coordinated water molecules. The identification of both the functional groups interactions in the MIR bands and the “ion-hopping bands” in the FIR bands for annealed Nafion samples can give new insights into the role played by the ionic interactions on the alpha of ionomer membranes. Such approach for understanding the relationship between the dynamics of aplha-relaxation and Nafion morphology is missing in the literature, possibly due to the incipient number of FIR studies of Nafion. The central objective of this work is to advance the understanding of the chemical features involved during the aplha-transition of in situ annealed Nafion membranes with the high-resolution mid (MIR) and far (FIR) infrared spectroscopy using the IRIS beamline of BESSY II synchrotron light source. Herein, the effect of short-term annealing of Nafion at RH ~ 0% and selected temperatures below and above the alphatransition is presented. The comparison between SAXS and FTIR data of Nafion membranes annealed in situ revealed that the alpha-transition is due to the long range motion of the ionomer chains via weakening of electrostatic interactions of the ionomer functional groups.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.