Structural and Spectroscopic Characteristics of a Proton-Conductive Ionic Liquid Diethylmethylammonium Trifluoromethanesulfonate [dema][TfOH]

Abstract

Structural specificity including dynamic behavior and stable conformations in the bulk phase of diethylmethylammonium trifluoromethanesulfonate [dema][TfOH], which is assumed to be a prominent ionic liquid electrolyte for non-humidified intermediate temperature fuel cells, have been investigated by 1H NMR, IR spectroscopic analyses, and molecular dynamics (MD) simulation. It is found that an N–H proton in [dema][TfOH] is an exchangeable mobile proton which can be substituted by D2O, and free rotation around the N–C bond in the ethyl side chain of the ammonium cation is retarded by ionic interactions between the cations and anions, therefore the methylene protons in the ethyl side chain are unisochronous. In addition, the rotational barrier of this N–C bond was observed to be 71 kJ mol−1, comparable to the barrier height of the amide N–C bond (which is well-known to have partial double bond character) from temperature-dependent NMR experiments by monitoring the peak-shape changes of methylene protons in the ethyl side chain of the ammonium cation. The bulk-phase structure of [dema][TfOH] was calculated by MD simulations on the basis of the OPLS-AA force field, and the evaluated structure was consistent with those of experimental results. Thus, IR spectrum frequency of the N–H proton, and the 1H NMR chemical shift values could be rationally assigned on the basis of the theoretically evaluated structures in the bulk phase.

Effects of a proton‐conducting ionic liquid on secondary ion formation in time‐of‐flight secondary ion mass spectrometry

“…This is also explainable in terms of the number of [dema][TfO] molecules, which are sources of protons, surrounding arginine molecules. As stated already, a [dema][TfO] molecule has a mobile proton; consequently, [dema][TfO] can work as a proton donor. On the other hand, an arginine molecule needs to accept a proton from surrounding molecules or ions to become a protonated arginine molecule.…”

“…Recently, we have performed SIMS experiments using a PIL, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), which has high protonic conductivity even at room temperature . Then, we reported that [dema][TfO] acted effectively as a primary ion beam as well as a liquid matrix to increase protonated secondary ions of arginine .…”

“…[8,44] Recently, we have performed SIMS experiments using a PIL, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), [45] which has high protonic conductivity even at room temperature. [46,47] Then, we reported that [dema][TfO] acted effectively as a primary ion beam as well as a liquid matrix to increase protonated secondary ions of arginine. [45] On the other hand, AILs, such as N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl) amide ([DEME][TFSA]) and 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl) amide ([EMIM] [TFSA]), were unsuccessful for use in SIMS.…”

Role of protic ionic liquid concentration in proton conducting polymer electrolytes for improved electrical and thermal properties

“…The 2800 cm −1 peak is due to the stretching of N-H group present in [dema] + ion when it is free while that of at 3067 cm −1 is due to its interaction with [TfO] − ions. The presence of these two peaks suggests a dynamical state of hydrogen bond network in the membranes containing higher concentration of PIL just as in the case of neat PIL [31,32]. This may have a direct influence over proton conductivity in these electrolytes.…”

Synthesis, characterization and electrochemistry of triethyl ammonium sulphate ionic liquid

“…It is evident from the figure that at wave number higher than 2700 cm −1 we can see two set of absorption bands in the range around 2660-2880 cm −1 and 3100-2900 cm −1 . The vibration due to CH stretching appears usually in 3100-2900 cm −1 range [25] and stretching vibration bands in this wave number region can be seen in the FT-IR spectra of triethylamine [26]. Where the absorption peaks in 2660-2890 cm −1 range that usually appear for NH stretching of ammonium cation [25] cannot be seen in the triethylamine FT-IR spectra [26].…”