Construction of ordered OH− migration channels in anion exchange membrane by synergizes of cationic metal-organic framework and quaternary ammonium groups

Summary A series of anion exchange membranes (quaternized chitosan/cation metal-organic framework [MIL-X-QCS]) were prepared via purposeful inserting the cationic metal-organic framework as the multifunctional filler into quaternized chitosan (QCS). The successful preparation of the anion exchange membrane was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Scanning electron microscope (SEM). In this research, we converted the charge-balanced MOFs skeleton Cr-MIL-101 into the cationic metal skeleton (Cr-MIL-101) + Cl − by anion stripping, and cooperated with quaternary amine groups to construct a high-speed OH − transmission channel. The introduction of a rigid MOF structure reduces the water uptake and swelling ratio of the composite membrane by 27% and 37%, respectively. At 80°C, the OH − conductivity of the MIL-9-QCS membrane (The composite membrane doped with 9 wt% Cr-MIL-101 crystals) reaches 2.30 × 10 −2 S·cm −1 and the power density reached its maximum (90.2 mW·cm −2 ), and the tensile strength reaches 20.12 MPa, which was higher than 18.7 MPa of Nafion-115 membrane. The spatial network structure of MOFs reduced the methanol permeability of MIL-9-QCS membrane by 24% compared with the original QCS membrane. Furthermore, the MIL-9-QCS composite membrane exhibited excellent alkali stability, where after being soaked in 2 mol L −1 NaOH solution at 60°C for 240 hours, its OH − conductivity still reached 77% of the initial value.