Probing Ion Exchange in the Triflic Acid–Guanidinium Triflate System: A Solid-State Nuclear Magnetic Resonance Study

Abstract

Knowledge of ion exchange and transport behavior in electrolyte materials is crucial for designing and developing novel electrolytes for electrochemical device applications such as fuel cells or batteries. In the present study, we show that, upon the addition of triflic acid (HTf) to the guanidinium triflate (GTf) solid-state matrix, several orders of magnitude enhancement in the proton conductivity can be achieved. The static 1 H and 19 F solid-state NMR results show that the addition of HTf has no apparent effect on local molecular mobility of the GTf matrix at room temperature. At higher temperatures, however, the HTf exhibits fast ion exchange with the GTf matrix. The exchange rate, as quantified by our continuum T 2 fitting analysis, increases with increasing temperature. The activation energy for the chemical exchange process was estimated to be 58.4 kJ/mol. It is anticipated that the solid-state NMR techniques used in this study may be also applied to other organic solid-state electrolyte systems to investigate their ion-exchange processes.

Ion Vacancies and Transport in 1-Methylimidazolium Triflate Organic Ionic Plastic Crystal

“…This liquid phase increases with increasing LiTFSI concentration and form an interconnected tortuous liquid pathway when the concentration exceeds the percolation threshold, yielding a sudden enhancement in ionic conductivity. Although this model seems to be valid for many OIPC systems doped with Li salts, 13 and other charge species such as Na 14 and H, 6,15 signs of amorphous or liquid phase presented, despite higher ionic conductivities. 16 The model of ion transport through vacancies and defects in OIPCs is logically sound and has been supported by DFT and MD calculations 17−19 as well as by positron annihilation lifetime spectroscopy (PALS) studies.…”

“…Note that H3 is a monoprotonated site; thus, the H3−H3 correlation must be attributed to intermolecular interaction. Besides, it is also interesting to see that while H2−H4 correlation peaks are clearly shown at about (7,15) and (8,15) ppm, the H2−H5 correlation peaks are absent, as highlighted by the green dots in the spectrum. The intramolecular distances between H2−H4 and H2−H5 are similar; both are ∼4.3 Å.…”

Proton Conducting Membranes Based on Poly(Ionic Liquids) Having Phosphonium Counter‐Cations

“…A key feature of protic ILs is that they have at least one dissociable proton on the cation which can support dynamic hydrogen bonding and allow proton transfer. [19,20] Similarly, the protic poly(ionic liquids) are expected to possess inherent proton ionic conductivities due to the presence of labile protons in their structures. Thus, the ionic conductivities of the polymers were determined by impedance spectroscopy from 30 to 90 °C.…”

Enhanced and Optically Switchable Proton Conductivity in a Melting Coordination Polymer Crystal

“…[17] TheR aman spectra of 1''-TfH-10 showed as harp and separated band at 1032 cm À1 ,w hich suggests the presence of Tf À anion in 1''-TfH-10 (Supporting Information, Figure S7). [20] This suggests that proton transport in doped sample is facilitated by CP framework over Brownian motion of TfH alone.Thus once all the protonic defects facilitating proton transport in CP backbone are saturated, further addition of TfH only contribute to increase in amorphous fraction in CP,r esulting in negligible enhancement in proton conductivity.T he activation energies for samples were calculated to be 1.12 (1''), 1.08 (1''-TfH-5), 0.97 (1''-TfH-10), and 0.93 (1''-TfH-15) eV.T he decrease in activation energy with increasing dopant amount supports the favorable role of TfH in enabling long-range proton hopping path in doped CP.T he 31 Ps olidstate NMR spectrum for 1'' and 1''-TfH-10 did not show distinct change on doping ( Supporting Information, Figure S12). Similar to 1'', all of the doped samples remain stable up to 200 8 8Cw ithout significant weight loss,s uggesting CP can hold TfH even on heating, which was further supported by isothermal gravimetric analysis (Supporting Information, Figures S9,S10).…”

“…TheT fH doped samples 1''-TfH-5 and 1''-TfH-10 showed as ignificant increase in proton conductivity over complete temperature range with conductivity values of 2.0 10 À4 Scm À1 and 3.0 10 À4 Scm À1 at 110 8 8C, respectively.H owever,o nly small increase in conductivity was observed upon further increasing the TfH amount in 1''-TfH-15, yielding conductivity values of 2.0 10 À7 Scm À1 at 30 8 8Ca nd 2.7 10 À4 Scm À1 at 110 8 8C, respectively.T he small increase in proton conductivity for 1''-TfH-15 compared to 1''-TfH-10 indicates that the upper limit for conductivity enhancement effect has attained. [20] This suggests that proton transport in doped sample is facilitated by CP framework over Brownian motion of TfH alone.Thus once all the protonic defects facilitating proton transport in CP backbone are saturated, further addition of TfH only contribute to increase in amorphous fraction in CP,r esulting in negligible enhancement in proton conductivity.T he activation energies for samples were calculated to be 1.12 (1''), 1.08 (1''-TfH-5), 0.97 (1''-TfH-10), and 0.93 (1''-TfH-15) eV.T he decrease in activation energy with increasing dopant amount supports the favorable role of TfH in enabling long-range proton hopping path in doped CP.T he 31 Ps olidstate NMR spectrum for 1'' and 1''-TfH-10 did not show distinct change on doping (Supporting Information , Figure S12). Also,n oc lear peak corresponding to acidic proton was observed in 1 Hs olid-state NMR of 1''-TfH-10 (Supporting Information, Figure S13).…”