Probing the ionic transport dynamics in ionic liquid incorporated CuBTC-Metal-Organic Framework based PVdF-HFP nanocomposite membranes

Abstract

CuBTC-Metal-Organic Framework (MOF) has been prepared by solvothermal synthesis method and ionic liquid (IL) 1-butyl-3 methylimidazolium tetrafluoroborate (BMIMBF4) has been incorporated at different wt% into the CuBTC-MOF. The composite nanofiller has been dispersed in poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) polymer electrolyte system. Shifting of FTIR vibrational modes of carboxylate group is due to metal-ligand bond elongation upon interaction of ions of IL with CuBTC-MOF. The binding energy of Cu spin-orbit peak increases with incorporation of IL as obtained from XPS spectra suggesting motion of BF4− anions of IL towards the Cu metal nodes of MOF. Periodic oscillation and coordination structure of Cu K-edge are observed in k-space and R-space scanning EXAFS data. Non-Debye dielectric relaxation dynamics is observed from dielectric permittivity and modulus spectra with ionic conductivity of 8.7 × 10−3 Scm−1at 50 wt% of IL incorporation in the composite polymer electrolyte at 380 K. The electrochemical stability profile increases with increasing IL concentration and attains 6.1 V at 50 wt% of IL.