Ionic 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 (H2 dobdc), H4 dobdc: 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 H2 O. Furthermore, the continuous increase in Li+ mobility with temperature contributed to the retention of the overall high ionic conductivity at high temperatures.
Keywords: Ionic Conductivity; Lithium Halide; Metal-Organic Frameworks; PFG NMR; Proton Conductivity.
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