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

• Published in: Angewandte Chemie International Edition Vol. 62; no. 19; pp. e202301284 - n/a
• Main Authors: Sarango‐Ramírez, Marvin K., Donoshita, Masaki, Yoshida, Yukihiro, Lim, Dae‐Woon, Kitagawa, Hiroshi
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 02.05.2023
• Edition: International ed. in English
• Subjects: Anions; Conduction; Conductivity; Durability; Halides; High temperature; Hydrogen; Insertion; Introduced species; Ion currents; Ionic Conductivity; Ionic liquids; Lithium; Lithium Halide; Lithium ions; Magnetic resonance; Metal-organic frameworks; Mobility; NMR; Nuclear magnetic resonance; PFG NMR; Proton Conductivity; Salts; Titanium; PFG NMR; Metal-Organic Frameworks; Ionic Conductivity; Proton Conductivity; Lithium Halide
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202301284

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(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. A high ionic conductivity (>10−2 S cm−1) was observed in the 2D‐Ti‐dobdc MOF after Li salt intercalation, which improved the H2O affinity of the frameworks, facilitating Li+ and H+ diffusion. Furthermore, the ion diffusion evaluated by PFG NMR indicates the counter anion effect. It was demonstrated that the moderate covalent/ionic character of LiBr and the high H2O uptake are crucial factors in efficient ionic conductors.