Chemical stability enhancement of crown ether grafted sulfonated poly(arylene ether ketone) fuel cell membrane by cerium ion fixation

In operation of polymer electrolyte membrane fuel cell or direct methanol fuel cell, ·OH radicals are the major cause for the degradation of polymer electrolyte membrane. In order to enhance its antioxidation stability, cerium ion (Ce³⁺, CE), an ·OH radical quencher, is introduced to membrane, as it converts the ·OH radicals into inactive chemicals. In this study, aminoethyl-15-crown-5 (CRE) is grafted on the sulfonated poly(arylene ether ketone) (SPAEK) to prevent the migration of CE ions from the membrane for long-term antioxidation stability, as CRE forms a coordination complex with CE. The chemical and physical structures of the CRE grafted SPAEK are examined using proton nuclear magnetic resonance, energy dispersive X-ray, and small-angle X-ray scattering spectroscopy. The physical properties of the CRE grafted SPAEK membrane are investigated and compared with those of the CRE blended and CE blended ones. While the grafting of CRE does not significantly affect the thermal and mechanical and water uptake behaviors of membranes, it leads to a significant improvement of antidegradation effect compared with other blend systems according to Fenton's test. The proton conductivity decreases with addition of CE but its effect is lessened by introduction of CRE.