Integration of a 2D Metal-Organic Framework with Functionalized Graphene

Abstract

Two-dimensional metal-organic frameworks (2D-MOFs) are low-dimensional hybrid organic-inorganic materials synthesized via coordinating planar multidentate ligands with metal nodes to form an extended coordination network. Such 2D-MOFs are emerging as next-generation 2D crystalline solids for energy-based applications. Similar to their 3D counterparts, 2D-MOFs exhibit high crystallinity and porosity, along with superior orbital overlap, which engenders them with efficient charge storage and facile charge transfer. However, for practical applications, the performance needs to be improved; therefore, combining 2D-MOF with various 2D matrices via chemical interaction is expected to enhance the overall electrical and/or electrochemical properties. Herein, we demonstrate an unconventional strategy to integrate a 2D-MOF, namely Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with functionalized graphene, i.e., reduced graphene oxide (rGO) by an in-situ reductionoxidation reaction. We have also carried out an in-depth comparative study with traditional methods. The composite, namely Cu-HHTP/rGO, was studied using techniques like Electron Spin Resonance (ESR), Raman, and X-ray Photoelectron Spectroscopy (XPS) for probing the possible chemical interaction. Cu-HHTP/rGO demonstrates a markedly high increment in electrical conductivity, along with a fourfold enhancement in BET surface area compared to pristine Cu-HHTP. The Seebeck coefficient suggests the change in semiconducting behavior from n-type in Cu3(HHTP)2 to p-type in Cu-HHTP/rGO, along with a high thermoelectric power factor. The Cu- HHTP/rGO composite was studied for supercapacitor application. The capacitance values were enhanced by almost two-fold in both solid and liquid state configurations, compared to pristine Cu-HHTP. We anticipate that the unconventional chemical approach proposed in this work can be used to combine various 2D-MOFs with different 2D matrices, which can then be explored for wide-scale applications.