High proton conductivity and structural robustness are critical for advancing proton exchange membrane fuel cells (PEMFCs) in sustainable energy technologies. Here, we present a pH-controlled synthetic strategy that yields two cadmium-based metal-organic frameworks (MOFs), Cd-FAIA-1 (neutral) and Cd-FAIA-2 (anionic), both derived from a common amide-functionalized tetra-carboxylate linker. Structural analysis shows that Cd-FAIA-1 adopts a layered framework incorporating water molecules, whereas Cd-FAIA-2 forms a porous network hosting both water molecules and dimethylammonium (Me2NH2+) cations. These structural distinctions enable solvent-assisted proton conduction, with conductivities of 3.64 × 10-4 S·cm-1 for Cd-FAIA-1 and 8.76 × 10-3 S·cm-1 for Cd-FAIA-2 at 80 °C and 98% relative humidity (RH). The superior performance of Cd-FAIA-2 stems from the Me2NH2+-assisted proton transport. To boost practical applicability, Cd-FAIA-2 was incorporated into a polyvinylpyrrolidone-polyvinylidene fluoride (PVP-PVDF) matrix to fabricate mixed matrix membranes (MMMs). Remarkably, the membrane with a 60 wt % MOF loading (Cd-FAIA-2@MMM-60) delivered a superprotonic conductivity of 3.21 × 10-2 S·cm-1 under identical conditions─surpassing the pristine MOF by a wide margin. This improvement is attributed to cooperative interactions among Me2NH2+ cations, water molecules, amide groups, and the polymer network. Furthermore, the gram-scale synthesis of these MOFs highlights their promise for integration into sustainable electrochemical devices, particularly fuel cells.
Bedi et al. (Wed,) studied this question.