The Host-Guest Assemblies of Metal-Organic Frameworks and Protic Ionic Liquids With ZIF-8 and [Dema][TfO] - Structural Response and Ionic Conductivity.

The synergy between ionic liquids (ILs) and metal-organic frameworks (MOFs) has attracted considerable attention because of future applications as a tailor-made hybrid ionic conductor. The incorporation of ILs into MOFs cages has led to the development of a novel type of solid electrolytes (ILs@MOF), characterized by exceptional thermal stability and high conductivity for large ionic species. In this study, an efficient capillary method was employed to introduce a classical protic IL, [Dema][TfO], into ZIF-8 pores, consisting of sodalite-type cages (Zn(MeIm)2). Our investigation focuses on the influence of varying ILs content on the free (pore) volume, thermal stability, microstructure, and ionic conductivity. The uptake of [Dema][TfO] results in a ZIF-8 cage expansion, accompanied by a decrease of the decomposition temperature. Upon infiltration of [Dema][TfO] into the ZIF-8 pores, the preexisting hydrogen bonds within the IL are broken due to confinement effects. Notably, when ZIF-8 pores are entirely saturated with [Dema][TfO], the composite material exhibits an ionic conductivity of 1.09(6) mS·cm-1 (at 160°C under anhydrous conditions) with an activation energy of 0.45(3) eV, which is better than other ILs@MOF conductive composites. These findings reveal ILs@MOF hybrid composites are versatile systems to compose protic conductors, attributable to their elevated ionic conductivity.