Effect of cerium/18-crown-6-ether coordination complex OH quencher on the properties of sulfonated poly(ether ether ketone) fuel cell electrolyte membranes

• Effect of Ce3+ ions on anti-oxidation properties of sPEEK fuel cell membrane was studied.
• Ce3+ ions quenched the hydroxyl radicals, the major oxidation promoter in fuel cell operation.
• Chemical degradation kinetics was noticeably prolonged by introduction of Ce3+ ions.
• Introduction of Ce3+ ions reduced the proton conductivity.
• But the presence of 18-crown-6-ether hosting the Ce3+ ions lessened its effect.

The effect of cerium ions (Ce3+) on the anti-oxidation and other properties of sulfonated poly(ether ether ketone) (sPEEK) membrane was studied, as it quenches the hydroxyl radicals, the major oxidation promoter in fuel cell operation. Cerium (Ce) was introduced along with 18-crown-6-ether to form a coordination complex to prevent both the migration of Ce3+ ions from the membranes and the direct interaction with sulfonic acid groups in sPEEK. The chemical and physical structures of the composite membranes were investigated using FT-IR, 1H NMR, SEM, EDX, and SAXS. As the concentration of Ce3+ ions increased, the distance between ion clusters of the membranes decreased by reduction of the strength of sulfonic acids interacted with the Ce3+ ions. The introduction of Ce3+ ions reduced the proton conductivity, but the presence of 18-crown-6-ether lessened the effect. According to Fenton׳s test, the pristine sPEEK membrane was completely degraded by oxidation in 24 h, but the composite membranes containing Ce3+/18-crown-6-ether complex were stable for up to 70 h. Other properties such as the thermal and mechanical stability and the water uptake were not noticeably affected by the presence of Ce3+ at the low concentration level of 2 mol% relative to sulfonic acid groups.