Nafion® nanocomposite membranes with enhanced properties at high temperature and low humidity environments

Abstract

Highly proton conductive nanocomposite membranes were synthesized by incorporating modified silica nanoparticles bearing different kinds of acid functionalities into Nafion. The short oligomeric corona, containing either phosphonate or sulfonate functional groups, leads to membranes with non-aggregated, discrete nanoparticles acting synergistically with the polymer. The new membranes exhibit significantly increased proton conductivity in all relative humidities and temperatures, however unprecedented behavior is observed at elevated temperatures (>80 °C) and/or low relative humidity. Pulse Field Gradient NMR measurements demonstrate that, in contrast to neat Nafion, which shows a precipitous decrease in the self-diffusion of water above 80 °C, the nanocomposite membranes were able to maintain high proton diffusivities pointing to adequate hydration levels for several hours at 130 °C without any external humidification. Furthermore, thermal and dynamic mechanical analysis reveal that the nanocomposite membranes retain their stiffness at much higher temperatures up to 200 °C compared to recast Nafion opening the way for high temperatures applications. The overall high ionic conductivity of the nanocomposite membranes especially above 80 °C coupled with their exceptional water retention capability and mechanical robustness makes them very attractive for potential use in fuel cell applications.