Water-mediated proton conductive properties of three water-stable metal-organic frameworks constructed by pyromellitic acid

Abstract

Selecting aromatic polycarboxylic acid ligands to self-assemble metal-organic frameworks (MOFs) with good water stability and proton conductivity is an expected preparation strategy. Herein, three proton conductive MOFs, 3D {[Zn2(1,2,4,5-BTA)](4,4′-tmdp)2]·5H2O}n (1) (1,2,4,5-H4BTA ​= ​1,2,4,5-benzenetetracarboxylic acid; 4,4′-tmdp ​= ​4,4′-trimethylenedipyridine), 2D {[Zn2(1,2,4,5-BTA)(4,4′-tmdp)(H2O)3]·2.25H2O}n (2), 3D {Cd(1,2,4,5-BTA)0.5}n (3) have been synthesized according to the literature method or hydrothermal method and structurally characterized by single-crystal X-ray diffraction and other approaches. All three MOFs have excellent thermal and water stability. EIS determinations show that with the increase of temperature and humidity, their proton conductivities gradually enhanced. Note that at 100 ​°C and 98% RH, their optimal proton conductivity values can attain about 10-4 ​S ​cm-1, which are higher than those of similar MOFs. Consequently, their proton conduction properties and mechanism were compared and speculated on the basis of activation energy calculation and crystal data analyses. We firmly believe that this research will provide new opportunities for the design and preparation of multicarboxylic acid-based crystalline proton conducting materials.