Effect of IL incorporation on ionic transport in PVdF-HFP-based polymer electrolyte nanocomposite doped with NiBTC-metal-organic framework
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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 (BMIMBF4) at varying weight ratios to use as nanofiller in the polymer matrix of poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). The structural 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 BF4− 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.
KeywordsMetal-organic framework Composite polymer electrolyte Ionic liquid Dielectric relaxation, AC conductivity
The authors sincerely acknowledge the financial support from DST-INSPIRE, Govt. of India through Grant No.: DST/INSPIRE Fellowship/2015/IF150994. Authors are also thankful to Professor S. N. Jha and Chandrani Nayak, Raja Raman Centre for Advanced Technology (RRCAT), Indore, India, for extending help in Scanning EXAFS and XANES facilities using synchrotron beamline.
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