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Structure and Ionic Conductivity Properties of Ionic Liquid@Metal—Organic Framework Composites



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Tuffnell, Joshua Mark 


IL@MOF (IL: ionic liquid; MOF: metal-organic framework) materials have been proposed as a candidate for solid-state electrolytes, combining the inherent non-flammability, high ionic conductivity, and high thermal and chemical stability of the ionic liquid with the host-guest interactions of the MOF. Although there is a large degree of chemical tunability of the MOF and IL components, the ionic conductivity of the IL in the composite is greatly reduced compared to the bulk due to the nanoconfinement of the IL within the nanopores of the MOF. In the literature, studies have been limited to modifications to the organic linkers or metal ions of the MOF, however, the structuring of the pore architecture can be modified in several ways, explored in this thesis. Firstly, the addition of disordered mesopores from sol-gel synthesis conditions resulted in a hierarchically porous MOF superstructure containing both micropores (innate to the MOF) and mesopores (formed by controlled drying of the sol-gel system) and affords greater IL filling capacities as measured by nitrogen gas sorption experiments. Electrochemical impedance spectroscopy was used to compare the ionic conductivities of hierarchically porous IL@MOF composite with a standard microcrystalline IL@MOF composite. The theme of superstructures was further explored by utilising artificial opal polystyrene templates to generate ordered (inverse opal) and disordered macroporous networks within the MOF particles. The limited mechanical stability of the inverse opal MOF structure meant that gentle IL infiltration conditions were required for successful composite formation. Finally, a study on how the interaction between the IL and MOF components affects the structural transitions in ‘breathing’ MOF materials using variable temperature X-ray diffraction was carried out. In particular, the presence of the ionic liquid was demonstrated to lead to a distinct crystal structure which undergoes a similar phase transformation, but at a lower temperature.





Bennett, Thomas
Dutton, Sian


ILs, Inverse Opal, Ionic Liquid, Metal-Organic Frameworks, MOF composite, MOFs, Solid-state electrolyte


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Engineering and Physical Sciences Research Council (1948666)