A Single Potassium-Ion Conducting Metal–Organic Framework

In this study, the 4-sulfobenzoic acid potassium salt is postsynthetically immobilized on the hexa-zirconium nodes of a zirconium-based MOF, MOF-808, by the solution-phase solvent-assisted ligand incorporation approach. With all of the sulfonate-based anions firmly immobilized within the rigid framework of MOF-808 along with mobile potassium ions present in the resulting material (MOF-808-SO3K), the MOF-808-SO3K-based solid-state electrolyte achieves an ionic conductivity of 3.1 × 10–5 S/cm at 303 K, a low activation energy of 0.32 eV, and a high transference number of 0.76 for potassium ions. The compound shows good long-term cycling stability with potassium metal during the charge–discharge processes. First-principles calculations are further performed to probe the structure of MOF-808-SO3K and gain insights into the ionic conduction of potassium ions in MOF-808-SO3K.