Metal organic framework composite anion exchange membranes sandwiched with graphitic phase carbon nitride for enhanced stability

The anti-swelling performance of ion exchange membrane in water is of importance in guaranteeing stable operation of the fuel cell. In this work, the purpose is to inhibit the swelling of anion-exchange membranes to further improve the dimensional stability of the membranes. IL@MOF-801 is first introduced into imidazole-functionalized poly-ether-ether-ketone (Im-PEEK) to obtain IL@MOF-801/Im-PEEK membranes. Sulfonated g-C₃N₄ (SGCN) is synthesized with the reaction of graphite-like phase carbon nitride g-C₃N₄ (GCN) and sulfamic acid. Then, the sandwiched composite membranes are obtained by encapsulating SGCN on the surface of 4 % IL@MOF/Im-PEEK membranes. The encapsulation of SGCN inhibits the movement of the Im-PEEK polymer backbone and the free volume of the membrane decreases. What's more, it results in the water uptake and swelling ratio of the composite membrane SGCN2-IL@MOF/Im-PEEK decreasing from 24.05 % to 9.55%, 16.91 % to 9.21 % after encapsulation respectively, which greatly limits the swelling of the membrane. The ionic conductivity of the membrane also increases to 126.77 mS/cm with the aid of the interaction between the sulfonic acid group of SGCN and the imidazole group of Im-PEEK, and the residual ionic conductivity is as high as 91.3 % after 14 days of immersion in alkaline environment.