4,4′-Oxydianiline (ODA) containing sulfonated polyimide/protic ionic liquid composite membranes for anhydrous proton conduction

The aim of this study was to utilize ionic liquids (ILs) in preparation of modified sulfonated polyimide (SPI) composite membranes to substantially increase the conductivity of proton exchange membranes (PEMs). Protic ILs used included 1-vinylimidazolium trifluoromethanesulfonate [ImVH][OTf] and 1-methyl-imidazolium trifluoromethanesulfonate [ImMH][OTf]. SPIs are synthesized from diamine, 2,2-bis[4-(4-amino-phenoxy)phenyl]propane (BAPP), sulfonated diamine, 4,4′-diamino diphenyl ether-2,2′-disulfonic acid (ODADS), and an aromatic anhydride, ODPA (4,4′-oxy diphthalic anhydride). ODADS improves conductivity, while BAPP enhances the mechanical and thermal properties of SPIs. We have prepared SPI/IL composite PEM using 50 wt.% [ImVH][OTf] with a high conductivity of 3–6 mS/cm at 120 °C and anhydrous condition depending on the ODADS content. [ImVH][OTf] offered better conductivity, which can be attributed to its chemical structure that has a vinyl group attached to an imidazolium ring to provide lower melting temperature and lattice energy, thereby increasing conductivity.