Development of sulfonated poly(ether ketone ether sulfone) (S-PEKES) as proton exchange membrane (PEM) for using in direct methanol fuel cell (DMFC)

Abstract

Poly(ether ketone ether sulfone) (PEKES),was synthesized by nucleophilic aromatic substitution polycondensation between bisphenol S and 4,4'-difluoro-benzophenone (system A), and between bisphenol S and 4,4'-dichlorobenzophenone (system B). Properties of both post-sulfonated polymers are compared with those of a commercial PEEK 150XF from Victrex and Nafion 117. Advantages of the synthesized PEKES is the better solubility of PEKES in H₂SO₄ relative to PEEK 150XF which results in higher sulfonation degrees, the carbonyl groups (-C=O) and the sulfone groups (-SO₂-) in polymer backbone, which promote the chain stiffness and thermal stability. The sulfonated polymer samples were characterized by FTIR, ¹H-NMR, TGA, and LCR meter, and the degree of sulfonation (DS) was determined. The ion exchange capacity (IEC), the water uptake (%), the dielectric permittivity (έ), and the electrical conductivity increase monotonically with increasing DS. The proton conductivity values of S-PEKES of the highest DS are comparable with that of Nafion 1 17. The methanol, mechanical and oxidative stabilities of S-PEKES and S-PEEK 150XF membranes are relatively higher than those of Nafion 117. Furthermore, the composite proton exchange membranes based on S-PEKES incorporated various types of zeolite such as molecular sieve 3A, 4A, 5A, and ZSM-5 were developed for using as proton exchange membrane.