Investigation the Effect of TiO2 Nanoparticles on Proton Exchange Membrane of sPEEK Used as a Fuel Cell Electrolyte Based on Phase Diagram

Sulfonated polyetheretherketone (sPEEK) membrane is a good alternative for Nafion membrane due to its low price and excellent chemical and physical properties. In this investigation, sPEEK and the composite of sPEEK with the TiO2 nanoparticles are prepared using the method of phase inversion. Different tests such as water uptake measurement, ion exchange capacity, degree of sulfonation, scanning electron microscopy images and electrochemical impedance spectroscopy are performed for characterization of the prepared membranes. Additionally, to evaluate thermodynamic instability of the prepared membranes in the presence of TiO2 nanoparticles as a hydrophilic additive, the Flory–Huggins theory is employed to theoretically draw the phase diagram. To this end, Hansen solubility parameters are calculated by the Van Krevelen method, and then the interaction parameters are determined. Using thermodynamic properties and phase diagram, the proton conductivity of sPEEK/TiO2 membrane are predicted. The results showed that with the addition of 0.5 wt% of TiO2 nanoparticles, the water uptake and proton conductivity significantly increased in comparison with pure sPEEK membrane. However, with increasing the concentration of the additive, the viscosity significantly increased, and the water uptake and proton conductivity decreased.