Ethylene oxide functionalization enhances the ionic conductivity of a MOF

Scientific Achievement

A synergistic approach, combining methods known to enhance solid-state conductivity, is applied to a MOF resulting in a true solid-state lithium conducting MOF system with ionic conductivity similar to reported MOF/Li salt/solvent electrolytes.

Significance and Impact

Varying the degree of EO functionalization of the zirconium MOF UiO-68 affords two novel MOFs; UiO-68-EO and UiO-68-2EO exhibit solvent-free ionic conductivity upon melt-loading LiTFSI in their pores. Incorporating EO chains provides a lithium ion migration pathway lined with oxygen coordination sites resulting in an ionic conductivity of 3.8 × 10−7 S cm−1 and 3.9 × 10−4 S cm−1 at 90 °C for UiO-68-EO/LiTFSI and UiO-68-2EO/LiTFSI respectively.

Research Details

  • The linkers for the two novel MOFs were synthesized via Suzuki coupling of 1,4-dibromobenzene derivatives, substituted with EO chains of different lengths, and 4-(methoxycarbonyl)phenyl boronic acid.
  • The salt loading was monitored via PXRD and DSC.
  • AC electrochemical impedance spectroscopy was used to determine the ionic conductivity of UiO-68-EO/LiTFSI and UiO-68-2EO/LiTFSI. UiO-68-2EO/LiTFSI, with larger EO chains, shows higher conductivity than UiO-68-EO/LiTFSI.

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DOI: 10.1039/D2CC01286C

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