ORIGINAL PAPER Effect of IL incorporation on ionic transport in PVdF-HFP-based polymer electrolyte nanocomposite doped with NiBTC-metal-organic framework Rituraj Dutta 1 & A. Kumar 1 Received: 21 March 2018 /Revised: 2 May 2018 /Accepted: 18 May 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Ni-based metal-organic framework (MOF), nickel 1,3,5-benzene tricarboxylate (NiBTC) has been synthesized by solvothermal method and incorporated with ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF 4 ) at varying weight ratios to use as nanofiller in the polymer matrix of poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). The struc- tural properties of MOF-NiBTC-based composite polymer electrolyte system upon IL incorporation have been investigated by XRD, FTIR, BET, scanning EXAFS and XANES techniques. Shifting of vibrational modes of –COOH groups is observed from FTIR spectra due to strong interaction of Ni metal cluster with BF 4 - anion of the IL. Local coordination structure and oscillation periodicity of Ni K-edge are investigated in R-space and k-space from the EXAFS as well as XANES spectra. Asymmetric oscillatory behavior with reduction in coordination number is observed upon IL incorporation due to strong interaction of guest IL with the host MOF-NiBTC. Dielectric relaxation and scaling of AC conductivity have been analyzed in the temperature range of 300–380 K and frequency range of 42 Hz–5 MHz. Non Debye type dielectric relaxation dynamics is observed due to short range hopping of ions. Ion concentration and temperature independent scaling behaviors are followed by the composite polymer electrolyte membranes. Optimum ionic conductivity of 6.5 × 10 -3 S cm -1 and electrochemical stability up to 5.7 V have been obtained at 50 wt% of IL incorporation in the porous nanocomposite electrolyte system. Keywords Metal-organic framework . Composite polymer electrolyte . Ionic liquid . Dielectric relaxation, AC conductivity Introduction Metal-organic frameworks (MOFs) are microporous hybrid nanomaterials composed of unsaturated inorganic metal clus- ters linked with organic linker molecules [1]. Due to their tremendous unique properties like high surface area, tunable topological geometry, controllable pore textures they are promising materials for various catalytic, sequestration, sens- ing and electrochromic applications [2]. MOFs can be treated as potential host materials for entrapping tiny guest molecules inside their micropores so that their phase behavior can be maintained by tunable guest-host interactions [3]. Ionic liq- uids (ILs) are highly stable room temperature molten salts composed of organic cations and inorganic anions with infi- nite structural variations. They have also special properties such as high electrochemical and thermal stability, low vapor pressure and high ionic conductivity [4]. ILs can be used as highly preferable ionic guest materials to incorporate in the micropores of MOFs so that strong interaction of ions of IL and MOF can control the phase dynamics of the composite system via nanosizing effect of IL [5]. Confinement of IL in the micropores of different MOF materials to enhance struc- tural as well as electrochemical properties has been reported by several researchers. Yifei Chen et al. [6] reported experi- mental as well as simulation work on confinement of IL 1- Butyl-3-methylimidazolium hexafluoro phosphate (BMIMPF 6 ) in IRMOF-1. The anionic part PF 6 - exhibits strong interaction with the Zn metal cluster while the cationic part BMIM + resides at the open pores and reacts with the organic ligands. Kazuyuki Fujie et al. [7] reported the con- trolled phase dynamics of the framework ZIF-8 by incorpo- rating IL EMI-TFSA in a view to enhance the electrochemical properties of the composite system. X-ray absorption near edge structure (XANES) and extended X-Ray absorption fine structure (EXAFS) are widely used techniques to elucidate the local structural geometry of the unsaturated inorganic metal * A. Kumar ask@tezu.ernet.in 1 Materials Research Laboratory, Department of Physics, Tezpur University, Napaam, Tezpur, Assam 784028, India Journal of Solid State Electrochemistry https://doi.org/10.1007/s10008-018-3999-7