High Proton Conductivity Achieved by Encapsulation of Imidazole Molecules into Proton-Conducting MOF-808.

Metal-organic frameworks (MOFs), as newly emerging materials, show compelling intrinsic structural features, e.g., the highly crystalline nature and designable and tunable porosity, as well as tailorable functionality, rendering them suitable for proton-conducting materials. The proton conduction of MOF is significantly improved using the postsynthesis or encapsulation strategy. In this work, the MOF-based proton-conducting material Im@MOF-808 has been prepared by incorporating the imidazole molecules into the pores of proton-conducting MOF-808. Compared with MOF-808, Im@MOF-808 not only possesses higher proton conductivity of 3.45 × 10-2 S cm-1 at 338 K and 99% RH, superior to that of any imidazole-encapsulated proton-conducting materials reported to date, but also good durable and stable proton conduction. Moreover, the thermal stability of H-bond networks is much improved owing to the water molecules partially replaced by higher boiling point imidazole molecules. Additionally, it is further discussed for the possible mechanism of imidazole encapsulation into the pores of MOF-808 to enhance proton conduction.