Microwave-Assisted Rapid Synthesis of Nanoscale MOF-303 for Hydrogel Composites with Superior Proton Conduction at Ambient-Humidity Conditions

Metal-organic frameworks (MOFs) have attracted extensive attention in the field of proton conduction and show great promise to be ideal alternative solid proton conductors. However, most of the MOF proton conductors are limited to operating at high-humidity conditions because their proton conduction is highly dependent on water molecules that act as proton-transfer media. Herein, we demonstrate the rapid and high-yield preparation of MOF-303 nanocrystals with controllable sizes from 500 to 50 nm through a microwave-assisted synthetic method. The nanocrystals doped with methanesulfonic acid (MeSA), MeSA@MOF-303, display high proton conductivity (σ) up to 10-2 S cm-1 at 98% relative humidity (RH). Most importantly, the MeSA@MOF-303-PVA hydrogels comprised of MeSA@MOF-303 nanocrystals with poly(vinyl alcohol) (PVA) are prominent proton-conducting materials with σ > 10-3 S cm-1 at ambient-humidity conditions. This study demonstrates an efficient approach for improving the water-retention capacity of porous proton conductors to further realize high proton conductivity at ambient and even lower humidity conditions.