Cooperative Proton and Li‐ion Conduction in a 2D‐Layered MOF via Mechanical Insertion of Lithium Halides

Abstract

AbstractIonic conduction in highly designable and porous metal–organic frameworks has been explored through the introduction of various ionic species (H+, OH−, Li+, etc.) using post‐synthetic modification such as acid, salt, or ionic liquid incorporation. Here, we report on high ionic conductivity (σ>10−2 S cm−1) in a two‐dimensionally (2D)‐layered Ti‐dobdc (Ti2(Hdobdc)2(H2dobdc), H4dobdc: 2,5‐dihydroxyterephthalic acid) via LiX (X=Cl, Br, I) intercalation using mechanical mixing. The anionic species in lithium halide strongly affect the ionic conductivity and durability of conductivity. Solid‐state pulsed‐field gradient nuclear magnetic resonance (PFG NMR ) verified the high mobility of H+ and Li+ ions in the temperature range of 300–400 K. In particular, the insertion of Li salts improved the H+ mobility above 373 K owing to strong binding with H2O. Furthermore, the continuous increase in Li+ mobility with temperature contributed to the retention of the overall high ionic conductivity at high temperatures.