Unique protonconduction 3D ZnII metal organic framework exposure to aquaammonia vapor to enhance conductivity

Abstract

Recently, metal–organic frameworks (MOFs) have been receiving increasing attention because their modular building blocks give them diversity and functional adjustability. MOFs have achieved excellent results as novel proton-conducting materials. However, there are relatively limited studies on the properties of proton-conducting MOFs that can be regulated by changing the test environment. Herein we explored the proton conductivity of a Zn^II MOF {[Zn₃(m-MOD)₂(H₂O)₆]·4H₂O}_n (ZS-1) (m-MOD = 2-(3-methoxy phenyl)-1H-imidazole-4,5-dicarboxylicacid) at humidity and aquaammonia vapor. ZS-1 has a 3D structure in the shape of a windmill, which contains hexagonal one-dimensional channels and a large number of free and coordination water molecules, providing convenient conditions for proton conduction. ZS-1 obtained an optimal conductivity of 1.38 × 10⁻³ S cm⁻¹ (100 °C) under 2 M aquaammonia vapor, which was about three orders of magnitude higher than the maximum conductivity under water vapor (5.31 × 10⁻⁶ S cm⁻¹, 100 °C-98% RH). The proton conduction mechanism is discussed in depth by combining the structural characteristics and related characterizations.