Free-standing polymer-metal-organic framework membrane with high proton conductivity and water stability

As a new class of porous material, polymer-metal-organic framework (polyMOF) has attracted tremendous interests owing to their combined advantages of polymer and crystalline MOF. However, the poor film-forming ability of polyMOF limits its widespread application, especially in membrane separation area. Herein, for the first time, we demonstrate the fabrication of freestanding polyMOF membrane. The polyMOF nanosheets are synthesized by a polymer-assisted self-inhibition crystal growth strategy. Followed by self-assembly through vacuum filtration, a 20 µm-thick free-standing polyMOF membrane is constructed. Benefiting from the inclusion of polymer with hydrophobic backbone and the continuously distributed non-coordinated hydrophilic groups along polymer chain, the polyMOF membrane attains excellent structure stability against water, as well as superior proton transfer property. Proton conductivity as high as 112 and 25.6 mS·cm−1 is obtained by this polyMOF membrane at 100% and 20% relative humidity (RH), respectively, which are two orders of magnitude higher than those of pristine MOF. The conductivity under low humidity (20% RH) is even over 8 times higher than that of commercial Nafion membrane (3 mS·cm−1). This study may provide some guidance on the development of polyMOF membranes.