Proton Exchange Membrane with Enlarged Operating Temperature by Incorporating Phosphonic Acid Functionalized and Crosslinked Siloxane in Sulfonated Poly(ether ether ketone) (SPEEK) Matrix

A novel proton exchange membrane which can be applied in the range of 25-140°C is prepared by incorporating phosphonic acid functionalized crosslinked siloxane in sulfonated poly(ether ether ketone) matrix from amino trimethylene phosphonic acid (ATMP), epoxycyclohexylethyltrimethoxysilane (EHTMS), and sulfonated poly(ether ether ketone) (SPEEK). EHTMS is introduced to chemically fix free ATMP as well as a cross-linker. And, the obtained membranes are immersed in deionized water to remove free ATMP. Fourier transform infrared and X-ray diffraction patterns suggest that ATMP is anchored into EHTMS and Si-O-Si network forms successfully. These membranes are thermally stable up to 220 °C and exhibit excellent dimensional stability and mechanical performance. The addition of ATMP not only increases the amount of proton transfer sites, but also provides proton transport units for membranes at elevated temperature and low relative humidity (RH) condition. The proton conductivity of AES-4 membrane reaches 0.114S cm -1 at 80 °C and 100%RH and 0.056 Scm -1 at 140 °C and 20%RH, respectively.