Novel sulfonated polyimide-nafion nanocomposite membranes: Fabrication, morphology and physiochemical investigations for fuel cell applications

Abstract

Herein, Nafion/sulfonated polyimide (SPI-x) composite membranes have been fabricated using different ratios of Nafion and SPI. The SPI was synthesized using 1, 4, 5, 8-Napthalenetetracarboxylic dianhydride (NTDA) via a one-step high-temperature imidization method in an inert atmosphere. The incorporation of SPI membrane with ion exchange capacity (IEC) of about 1.0 mmol−1 in Nafion showed improvement in physicochemical properties, such as IECs, hydrolytic/oxidative stability, water uptake, and dimensional changes (3.61). Nafion/SPI-x composite membranes showed good proton exchange nature i.e. proton conductivity and thermal stability. Scanning electron micrographs (SEM) reveals that the Nafion/SPI-x nanocomposites membranes display well defined micro-phase separation morphology based on SPI content in the composites. Fourier-transform infrared spectroscopy (FT-IR) confirmed the presence of important functional groups in synthesized membranes. The protons present in membranes were studied by nuclear magnetic resonance (1H NMR) spectroscopy, carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy, and X-ray diffraction analysis (XRD) investigated the nature of polymer material. The thermal stability of the synthesized membranes was found up to be 500–550 °C by thermogravimetric analysis (TGA), a clear indication of good thermal stability of synthesized membranes. Among all Nafion/SPI composites with 60 and 80 wt.% of SPI show good morphology for membranes because of cross-linking between Nafion and SPI. In conclusion, the findings revealed that Nafion/SPI-x membrane could be used as a polymer electrolyte membrane (PEM) for direct methanol fuel cells (DMFCs) applications.