Optimization of sPEEK/S-TiO2 nanocomposite membranes using response surface methodology for low-temperature fuel cell

Polyether-ether-ketone (PEEK), a speciality thermoplastic polymer is treated with concentrated sulfuric acid to introduce sulfonated repeating units in its backbone. Sulfonated polyether-ether-ketone (sPEEK) is then compounded with sulfonated titanium dioxide (S-TiO 2 ) nanoparticles according to design of experiments (DoE). FT-IR spectra for sPEEK/S-TiO 2 nanocomposite membranes show the strong presence of peaks at 3500 cm −1 and 1632 cm −1 wave number because of bending and stretching vibrations of OH-group confirm successful sulfonation of polyether-ether-ketone polymer. Insertion of -SO 3 H group in polymer backbone hinders the stereo regularity of polymer chains and leads to an amorphous structure as confirmed by X-ray diffraction and transmission electron microscopy of membranes. Thermogravimetric analysis shows that the thermal stability of sPEEK is much poor than its precursor PEEK due to the presence of easily degradable -SO 3 H groups. Analysis of variance (ANOVA) results show that factor wt.% of S-TiO 2 is the most influencing among the factors. The proton conductivity and ion exchange capacity (IEC) increase with wt.% of S-TiO 2 . Proton conductivity of pristine sPEEK is 31.1 mS/cm which significantly increased to be 60.7 mS/cm for sPEEK/S-TiO 2 (0.10 wt%) nanocomposite membrane. IEC, water uptake, and swelling ratio were observed to increase with the addition of S-TiO2 (wt.%) in the sPEEK matrix, reaching values of 62.6 mmol/g, 11.6 %, and 18.6 %, respectively. • The additive of S-TiO 2 in sPEEK to enhance proton conductivity of the fuel cell. • SPEEK/S-TiO 2 nanocomposite membranes were prepared according to DoE. • Effects of factors S-TiO 2 , mixing temperature and sPEEK concentration were studied. • DoE responses are proton conductivity, IEC, water uptake and swelling ratio. • The ANOVA results showed S-TiO 2 is statistically determined as a significant term.