Design and Preparation of a Superior Proton Conductor by Confining Tetraethylenepentamine in the Pores of ZIF-8 to Induce Further Adsorption of Water and Carbon Dioxide

In this work, we present a new strategy toward the design and preparation of a metal-organic framework- or porous coordination polymer-based superior proton conductor. We chose a robust metal-organic framework, ZIF-8, as the host and a flexible aliphatic alkylpolyamine, tetraethylenepentamine (TEPA), as the guest, and we successfully prepared an encapsulation compound TEPA@ZIF-8 via the facile insertion of TEPA into the pores of ZIF-8, which was characterized by microanalysis, thermogravimetric analysis, IR spectroscopy, N₂, water vapor adsorption-desorption, and other methods. Each cage in ZIF-8 is occupied by ∼1.44 TEPA molecules, and the introduced TEPA further adsorbs H₂O and CO₂ from air to offer a superior proton conductor, TEPA@ZIF-8-H₂CO₃, with σ = 2.08 × 10^-3 S cm^-1 at 293 K and 99% relative humidity, and excellent proton conduction durability. Regarding ZIF-8, the proton conductivity of TEPA@ZIF-8-H₂CO₃ increases by 3 orders of magnitude at the same condition, and the activation energy decreases by 0.91 eV. Remarkably, TEPA@ZIF-8-H₂CO₃ also shows promising features for the detection of aqueous ammonia. This work provides more opportunities to achieve superior protonic conducting materials and suggests that MOF-based proton conductors possess great potential for applications in ammonia sensing.