| In this study, various novel proton-conducting membranes were prepared and investigated for PEMFC applications. These membranes consist of polysilsesquioxanes (empirical formula of R-Si-(O)1.5) that consist of a highly cross-linked Si-O backbone and a pendant organic side chain R, comprising propyl sulfonic or ethyl phosphonic acid groups. These polysilsesquioxane membranes were prepared by facile sol-gel processing using a wide selection of silane precursors, allowing fine-tuning of properties required for proton exchange fuel cell membrane applications. These inorganic-organic hybrid materials take advantage of the thermal/mechanical/chemical stability brought by the inorganic component, and the flexibility and proton-conducting properties of the organic component.; The propyl sulfonic polysilsesquioxane membranes exhibited good proton conductivity (10-2 S/cm) under various relative humidity conditions and temperatures. The proton conductivity of these membranes increased with an increased amount of acid content and relative humidity conditions, indicating its strong dependence on the presence of water. Additives like nanometersized metal oxide particles (SiO2 and TiO2) and synthesized polymeric phthalocyanine (polyPc) have been incorporated in the membranes, offering enhanced water uptake and mechanical stability, respectively. The ethyl phosphonic acid polysilsesquioxane membranes, also prepared via a straightforward sol-gel processing route, exhibited better thermal stability but lower proton conductivity (10-3 S/cm) at the same conditions compared to their sulfonic acid counterparts. Incorporation of polyPc in the membranes significantly improved the membranes' mechanical stability. |
