Metal-organic framework composite membrane for fuel cell applications at high temperature and low humidity

Advancement of new proton exchange membranes (PEMs) that work under anhydrous condition is one of the most critical requirements for proton exchange membrane fuel cells (PEMFCs) technology [1]. PEMFCs which can work under anhydrous conditions and temperature higher than 100 °C resolve substantially certain problems such as water and heat management, CO poisoning and amended electrode kinetics [2]. For this reason, many attempts have been made for developing new high-temperature polymeric electrolytes with high thermal and mechanical properties, high oxidative resistance and high proton exchange properties when doped with a strong acid [3]. So in this work a proton-conducting sulfonated poly(ether sulfone)-MOF membrane (SPES-MOF membrane) with high proton conductivity at high temperature and anhydrous conditions was synthesized by anchoring the Cr-MIL-101-NH2 to the aromatic polymer backbone via a Hinsberg reaction. The effect of MOFs as the pendant porous aminated moieties on membrane features such as water uptake; swelling ratio; mechanical, oxidative and thermal stabilities; morphology; acid retention capacity; ion exchange capacity; long-term durability; hydrogen crossover; proton conductivity and fuel cell performance was methodically studied. The presence of holes and -NH2 groups in MOFs structure enhanced the acid retention capacity of the SPES-MOF membrane. This resulted in satisfactory performance of the membrane at high temperatures and low humidity (the proton conductivity of membrane reached 0.041 S.cm-1 (compared to Nafion = 0.0029 S.cm-1) at 160 °C). Moreover, the crosslinking produced by MOFs increased the dimensional stability (the swelling ratio was reduced from 57% to 4%), oxidative resistance, tensile strength, and also improved water uptake and hydrogen crossover of the polymer.