High-temperature proton exchange membrane with dual proton transfer channels by incorporating phosphonic acid functionalized siloxane into poly(2,6-dimethyl-1,4-phenyleneoxide) (PPO)

A series of high-temperature proton exchange membranes were prepared by incorporating phosphonic acid functionalized siloxane synthesized from Amino Trimethylene Phosphonic Acid (ATMP) and 3-Aminopropyltriethoxysilane (APTES) into cross-linked 1-Methylimidazole-functionalized poly(2,6-dimethyl-1,4-phenyleneoxide) (PPO) backbone. The structural characteristics of membranes were investigated using FT-IR, 1H NMR and XRD, indicating that ATMP and backbones of membranes were successfully immobilized into cross-linking Si-O-Si networks formed by hydrolysis-polycondensation of APTES. The resultant membranes named as HTM-X exhibited superior oxidative resistance, mechanical properties and dimensional stability, even the thermal stability was up to 210 °C. The proton conductivities of membranes were also measured under different temperature. The result showed that HTM-15 membrane, whose content of phosphonic acid functionalized siloxane was 15 wt%, possessed the highest proton conductivity of 8.48 × 10−2 S cm−1 at 160 °C and low relative humidity (5%) with the contribution of dual proton transfer channels of acid-base pairs and continuous hydrogen bond networks. Therefore, this novel membrane acts as a potential candidate for proton exchange membranes operating at elevated temperature.