High performance proton exchange membranes with double proton conduction pathways by introducing MOF impregnated with protic ionic liquid into SPEEK

Abstract

Metal-organic frameworks (MOFs) have great advantages in proton conduction due to their unique structures. Both the pores in the MOFs and the outer surface of the MOFs can be modified to conduct protons. In this paper, MIL-125-NH2 was used to support protic ionic liquid ([DBUH][BO2]) and introduced into sulfonated poly (ether ether ketone) (SPEEK) substrate to prepare novel proton exchange membranes. Inside the MOF, the cation of the ionic liquids and water molecules can form hydrogen bonds to achieve proton conduction. Meanwhile, the –NH2 groups on MIL-125-NH2 can form hydrogen bonds with the –SO3H groups on SPEEK to facilitate proton conduction outside the MOF. Due to the double proton conduction paths within the hybrid membranes, the highest proton conductivity of IL@MIL-125-NH2/SPEEK-5 is up to 0.32 S cm−1, which is much higher than that of many reported proton exchange membranes. In addition, IL@MIL-125-NH2/SPEEK-5 has good oxidation stability and proton conduction stability by the addition of MIL-125-NH2. This study provides novel insight into the preparation of stable proton exchange membranes with high proton conductivity.