A Sodium-Based Phosphonates Metal–Organic Framework with Superprotonic Conductivity

A novel alkali metal-based metal–organic framework (Na-MOF) has been successfully prepared under solvothermal conditions using tetrakis(4-phosphonatophenyl)ethylene (H₈TPE) as a ligand and NaOH as a metal source. The single crystal structure of Na-MOF showed that the phosphonate groups and solvent water molecules formed a two-dimensional hydrogen bonding network. The phosphonic acid group has the ability to induce proton adsorption and release, forming an H-bonding network of proton conduction channels inside the metal phosphonate for efficient proton transport. The results showed that the proton conductivity of Na-MOF increased with the increase in temperature and relative humidity (RH). Na-MOF exhibits superprotonic conductivity of 1.03 × 10^–1 S·cm^–1 at 60 °C and 98% RH. As a solid-state proton conductor, its high proton conductivity shows good application prospects.