Charge percolation in metal-organic framework (HKUST-1)‒graphene nanocomposites

Abstract Modulating the conductivity of microporous metal-organic frameworks (MOFs) through formulation of composites with graphene (G), as the conductive element, is demonstrated, without being limited to a particular MOF composition or topology. The synthesis allows for varying G content within the composite systematically, resulting in highly electrically conductive composites beyond 30 wt% G. The charge percolation model can effectively be utilized to describe the macroscopic electrical conductivity of the synthesized composites. Starting from a non-conductive MOF (HKUST-1, σ = 2*10−8 S m−1), enhanced conductivity can be accessed through increasing the G wt%, reaching more than nine orders of magnitude increase in conductivity up to 23.3 S m−1 for the composite containing 59.4 wt% G. A charge percolation threshold of 30 wt% G was observed, where sufficient G-G contacts were established within the composite. The ab initio DFT calculations on Cu-paddlewheel@G model indicated several non-covalent interactions, including OH⋯π and π‒π interactions, governing the deposition of the MOF on top of G (range of ‒101.3 kJ/mol to −113.8 kJ/mol). This approach is potentially transferable to the vast majority of MOFs, as surface functionalization of the conductive filler is not a prerequisite for the attainment of bottom-up assembly of the MOF@G.