NMR investigation on nanocomposite membranes based on organosilica layered materials bearing different functional groups for PEMFCs

摘要

2D-layered materials are emerging as promising fillers for the preparation of high-performance composite membranes for PEMFCs systems combining excellent hydrophilic properties and thermal stability at high temperatures. Here we report the fabrication of a class of organosilica layered materials, bearing two different functional groups (SO3- and PO3-, by a simple, one-pot thermal treatment. These materials were incorporated into the Nafion matrix for the preparation of hybrid electrolytes showing remarkable transport properties, especially at harsh conditions. Powder XRD and FT-IR reveal the complete exfoliation of filler's layers into Nafion matrix. Water dynamics investigation, carried out via NMR spectroscopy (diffusivity and relaxation times), demonstrates that the hydrophilic nature of synthesized filler leads to improved transport properties and water retention capacity of the composite electrolyte, particularly at high temperatures. Both Nafion composites exhibit considerable water diffusivity after several hours at 130 degrees C in "dehydrated" condition. The enhanced performances of the nanocomposite membranes are further confirmed by EIS investigation. The composite membrane containing 3% of sulfonated filler at RH 30% and 120 degrees C exhibits a proton conductivity value four times higher than the pristine polymer membrane. Finally, TGA and DMA analysis unveiled that the dispersion of silica layers into the polymer matrix produce a remarkable improvement in the thermal resistance of the electrolyte. The synergy between improved proton transport properties under dehydrated conditions and enhanced thermal resistance proposes these composite membranes as potential effective electrolytes able to extend the operating temperature of PEMFCs systems. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.