Achieving Amphibious Superprotonic Conductivity in a Cu^I Metal–Organic Framework by Strategic Pyrazinium Salt Impregnation

Abstract

Treatment of a pyrazine (pz)-impregnated Cu^I metal-organic framework (MOF) ([1⊃pz]) with HCl vapor renders an interstitial pyrazinium chloride salt-hybridized MOF ([1⊃pz⋅6 HCl]) that exhibits proton conductivity over 10^-2 S cm^-1 both in anhydrous and under humid conditions. Framework [1⊃pz⋅6 HCl] features the highest anhydrous proton conductivity among the lesser-known examples of MOF-based materials exhibiting proton conductivity under both anhydrous and humid conditions. Moreover, [1⊃pz] and corresponding pyrazinium sulfate- and pyrazinium phosphate-hybridized MOFs also exhibit superprotonic conductivity over 10^-2 S cm^-1 under humid conditions. The impregnated pyrazinium ions play a crucial role in protonic conductivity, which occurs through a Grotthuss mechanism.