Abstract

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 °C, 95% RH, and 3.403×10−3 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 1.182×10−3 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.

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