Superionic Conduction over a Wide Temperature Range in a Metal-Organic Framework Impregnated with Ionic Liquids.

ABSTRACT

Most molecules in confined spaces show markedly different behaviors from those in the bulk. Large pores are composed of two regions an interface region in which liquids interact with the pore surface, and a core region in which liquids behave as bulk. The realization of a highly mobile ionic liquid (IL) in a mesoporous metal-organic framework (MOF) is now reported. The hybrid shows a high room-temperature conductivity (4.4×10-3  S cm-1 ) and low activation energy (0.20 eV); both not only are among the best values reported for IL-incorporated MOFs but also are classified as a superionic conductor. The conductivity reaches over 10-2  S cm-1 above 343 K and follows the Vogel-Fulcher-Tammann equation up to ca. 400 K. In particular, the hybrid is advantageous at low temperatures (<263 K), where the ionic conduction is superior to that of bulk IL, making it useful as solid-state electrolytes for electrochemical devices operating over a wide temperature range.