Synthesis and proton-conductive behaviour of two MOFs with covalently bonded imidazoles in the channels

Immobilization of imidazole molecules as proton carriers into MOFs to facilitate proton conduction is a general strategy for developing high proton conductive materials. Herein, we designed two imidazole substituted phthalic acid ligands and constructed two novel MOFs, {[Zr₆(OH)₁₆(H₃L₁)₄]Cl₈·20H₂O}_n [Zr-MOF; H₃L₁ = 2-(1H-imidazol-4-yl) methylaminoterephthalic acid] and {Gd(HCOO)(H₂L₂)₂}_n [Gd-MOF; H₃L₂ = 5-(1H-imidazol-4-yl)methylaminoisophthalic acid] and fully studied their porous nature, stability and water-assisted proton conduction. The resulting Zr-MOF exhibits a high proton conductivity of 1.82 × 10^-2 S cm^-1 at 98% RH and 80 °C, while Gd-MOF has a proton conductivity of 3.01 × 10^-3 S cm^-1 at 98% RH and 60 °C.