Fenton Stability of Mesoporous Ceria–Silica and Its Role in Enhanced Durability of Poly(arylene ether sulfone) Multiblock Copolymer Composite Membranes for Perfluorosulfonic Acid Alternatives

To increase the stability of cerium scavengers, we doped cerium oxide on mesoporous silica powders for the application of an oxidative stabilizer. The oxidation-reduction reaction involving hydroxyl radicals (^•OH) is investigated with Fenton's test using eight types of Ce(IV)-mobile compositions of matter 41 (MCM-41) and Ce(III)-MCM-41 powder samples. As confirmed by X-ray photoelectron spectroscopy, the relative amount of Ce³⁺ inside the mesoporous samples decreases with the increasing time of treatment using the Fenton solution, whereas that of Ce⁴⁺ increases. ²⁹Si CP-MAS NMR shows that the condensation of the siloxane bond varies according to the treating time up to 120 h. The mesoporous structure is also analyzed using synchrotron small-angle X-ray scattering and nitrogen adsorption. Further treatment with propane sulfonic acid ensured that the ionic conductivity of the sulfonated mesoporous silica did not decrease. The surface-modified mesoporous silica was incorporated in sulfonated poly(arylene ether sulfone) multiblock membranes. The sulfonated mesoporous silica could overcome the drawbacks of transition metal scavengers, such as a drop in ionic conductivity. Through experiments, we determined that the Ce-doped sulfonated mesoporous silica/sulfonated poly(arylene ether sulfone) composite membranes exhibit high oxidation stability when exposed to hydrogen peroxide and even higher proton conductivity than Nafion at a relative humidity over 60%.