Oxadiazole-based ligands are highly attractive for constructing metal–organic frameworks (MOFs) due to their polar, heteroatom-rich nature, which offers strong hydrogen-bond-accepting and dipolar sites, thereby enhancing host–guest interactions and facilitating efficient guest encapsulation. In this study, two oxadiazole-functionalized MOFs, CdMOF-1 and CdMOF-2, were synthesized and exhibited distinct architectures: a 2D layered structure and a doubly interpenetrated 3D framework, respectively. These structures feature well-defined hydrogen-bonded water columns and water–methanol channels, contributing to their notable water and thermal stability. Motivated by these structural attributes and robustness under experimental conditions, their proton conduction properties were systematically investigated. The pristine pelletized samples display proton conductivities of 3.21 × 10 –4 and 8.26 × 10 –4 S cm –1 at 80 °C and 98% relative humidity. Remarkably, incorporation into PVP–PVDF mixed-matrix membranes significantly enhances conductivity, achieving 7.61 × 10 –3 S cm –1 (ca. 24-fold increase) for CdMOF-1 and 9.32 × 10 –3 S cm –1 (∼11-fold increase) for CdMOF-2 under identical conditions. The low activation energies (<0.40 eV) observed for both the pristine MOFs and their corresponding membranes indicate a proton transport mechanism governed by the Grotthuss pathway.
Pal et al. (Sun,) studied this question.