Construction of well interconnected metal-organic framework structure for effectively promoting proton conductivity of proton exchange membrane

To obtain proton exchange membrane (PEM) with high proton conductivities under both high humidity and anhydrous condition, interconnected UiO-66-NH2 was tethered onto graphene oxide (GO) surfaces, and then incorporated into Nafion matrix. Thanks to tethering effect of GO surfaces and interconnection among MOF grains, well interconnected metal-organic framework (MOF) structures (GO@ UiO-66-NH2) were constructed. The structural advantage and mechanism of GO@ UiO-66-NH2 in proton conduction were explored. It was found the synergistic effect between GO and UiO-66-NH2 with suitable particle size was especially important for promoting proton transfer. Such interconnected structure of MOF on GO also made acid/base pair pathways between -SO3H of Nafion and -NH2 of GO@ UiO-66-NH2 more consecutive. This was favorable to proton conduction via both vehicle mechanism and Grotthuss mechanism. The proton conductivity of the as-prepared composite membrane reached up to 0.303 S/cm under 90 degrees C, 95% RH, and 3.403x10(-3) S/cm under anhydrous condition, which was about 1.57 and 1.88 times higher than that of the recast Nafion (0.118 S/cm and 1.182x10(-3) S/cm), respectively. Furthermore, the composite membrane showed a reduced methanol permeability, which was attributed to the barrier effect of the two-dimensional GO and the trapping of methanol by UiO-66-NH2 pores.