Conductive metal-organic frameworks (MOFs) and possible applications

Abstract: Metal-organic frameworks (MOFs) are a class of hybrid organic/inorganic materials with permanent porous structure. Whilst there are virtually endless possible selection of metal ions and organic ligands to build up a MOF structure, intrinsically conductive MOFs are rare, relatively new, and our knowledge on their conductivity and charge transport mechanisms is limited. Crystalline porous structure with intrinsic electrical conductivity gives new dimension for applications of MOFs. Therefore, it is very important to improve our understanding of conductivity principles, charge transport mechanisms and measurement methods to be able to compare different MOFs in electrical properties.We measured conductivity of a completely new bismuth-based MOF synthesized at Uppsala university (UU-200) to investigate the possibility of utilizing this material for chemiresisitive applications since it has selective adsorption for CO2 and SF6. We used Cu3(HHTP)2 as our reference MOF to establish the conductivity measurement method and compare our results with previous studies.Four-point probe conductivity measurements on pressed pellets of Cu3(HHTP)2 MOF showed that our method is chosen and performed correctly. The measured conductivity values for Cu3(HHTP)2 increased from 0.0022 S cm-1 to 0.0187 S cm-1 with decrease in porosity of the synthesized MOFs. We used identical parameters and condition for conductivity measurements of UU-200 samples which resulted in conductivity values of 2.37 x 10-6 S cm-1 and 5.78 x 10-6 S cm-1. These results show that firstly, considering UU-200 for chemiresistive applications cannot be ruled out; and secondly, the large difference in conductivity values of two similar materials can be related to anisotropic characteristics of UU-200’s 3D structure.