The proton dynamics of imidazole methylphosphonate: an example of cooperative ionic conductivity

Traer, Jason W.; Goward, Gillian R.

doi:10.1039/b917360a

Cited by 25 publications

(33 citation statements)

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“…Its rapid increase in phase II indicates its larger temperature dependence and may be partly ascribed to the increasing rotational disorder of the imidazolium cation in the relevant temperature range as observed before. 25,45 In addition, it jumps at 188 C corresponding to the phase I / melt transition and then rises steadily in the melt state up to 8.85 Â 10 À2 S cm À1 at 200 C. Particularly, a liquid-like ionic conductivity of 1.0 Â 10 À2 S cm À1 is reached at 185 C, again indicating the high disorder of 1 in phase I. One possible explanation for higher ionic conductivity in more disordered phases may be that the disordering or rotational motion creates vacancies, facilitating the motion of ions.…”

Section: Ionic Conductivitymentioning

confidence: 99%

“…imidazolium methylphosphonate) at ambient temperature has been demonstrated earlier. 45,58 Furthermore, a vehicle mechanism has been postulated to govern the proton conduction for 1 in the molten state with the imidazolium cation as a vehicle. 40 The activation energy (E a ) for each phase was calculated using the following Arrhenius equation:…”

Section: Ionic Conductivitymentioning

confidence: 99%

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Imidazolium methanesulfonate as a high temperature proton conductor

2013

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Imidazolium methanesulfonate (1) has been studied as a model proton conductor for high temperature polymer electrolyte membrane fuel cells (PEMFCs). It is found that 1 undergoes transformation from crystalline to plastic crystalline and then molten states successively from ambient temperature to 200 C.The solid-solid phase transition of 1 at 174 C has been preliminarily verified by differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). At the melting point of 188 C, 1 displays a low entropy of fusion of around 24 J mol À1 K À1 . In particular, a high ionic conductivity of 1.0 Â 10 À2 S cm À1 is reached at 185 C in the plastic phase. The activation energy for ionic conduction decreases as 1 is heated from the crystal phase to the melt phase. In the molten state, the contribution of protons to the ionic conductivity of 1 was corroborated electrochemically. In addition, 1 is electrochemically active for H 2 oxidation and O 2 reduction at a Pt electrode while it shows a high electrochemical window of 2.0 V. Furthermore, a NafionÒ membrane has been successfully doped with 1, as identified by infrared spectroscopy, powder XRD, grazing incidence XRD and thermogravimetric analysis. To the best of our knowledge, this may be the first report on a protic organic ionic plastic crystal (OIPC) consisting of protonated imidazole (C 3 H 5 N 2 + ) and an organic anion. The good thermal stability, high ionic conductivity, wide electrochemical window, favorable plastic crystal behavior and simple synthesis make 1 a highly interesting model proton conductor for high temperature PEMFCs.

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Section: Ionic Conductivitymentioning

confidence: 99%

Section: Ionic Conductivitymentioning

confidence: 99%

Imidazolium methanesulfonate as a high temperature proton conductor

2013

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“…[17][18][19] In addition, high risk of platinum catalyst poisoning, which arises from binding with carbon monoxide, is typically associated with current operating temperatures of PEMFCs. 1,[18][19][20][21][22] One solution under consideration to improve the performance is to design a suitable electrolyte that can operate above the typical temperature and relative humidity limits, the so-called ''hot, dry'' conditions. [22][23][24][25] Phosphate-based solid-acid electrolytes have demonstrated the capability of conducting protons under anhydrous conditions at elevated operating temperatures.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of benzimidazole ethylphosphonate: a solid-state NMR study of anhydrous composite proton-conducting electrolytes

Yan

Almeida

Traer

et al. 2013

Phys. Chem. Chem. Phys.

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Imidazole phosphate and phosphonate solid acids model the hydrogen-bonding networks and dynamics of the anhydrous electrolyte candidate for proton exchange membrane fuel cells. Solid-state NMR reveals that phosphate and phosphonate anion dynamics dominate the rate of long-range proton transport, and that the presence of a membrane host facilitates proton mobility, as evidenced by a decreased correlation time of the composites (80 ± 15 ms) relative to the pristine salt (101 ± 5 ms). Benzimidazole ethylphosphonate (Bi-ePA) is chosen as a model salt to investigate the membrane system. The hydrogen-bonding structure of Bi-ePA is established using X-ray diffraction coupled with solid-state (1)H-(1)H DQC NMR. The anion dynamics has been determined using solid-state (31)P CODEX NMR. By comparing the dynamics of ethylphosphonate groups in pristine salt and membrane-salt composites, it is clear that the rotation process involves three-site exchange. Through data interpretation, a stretched exponential function is introduced with the stretching exponent, β, ranging 0 < β ≤ 1. The (31)P CODEX data for pristine salt are fitted with single exponential decay where β = 1; however, the data for the membrane-salt composites are fitted with stretched exponential functions, where β has a constant value of 0.5. This β value suggests a non-Gaussian distribution of the dynamic systems in the composite sample, which is introduced by the membrane host.

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“…NMR spectroscopy investigations have been used to improve the understanding of the morphology of PEMs (Mauritz and Moore, 2004), the state and behaviour of water within them, and the mechanisms of proton conduction (Traer and Goward, 2010;Ye et al , 2006;Akbey et al , 2009). These studies utilize NMR experiments to act as molecular-level probes of bulk or average material properties.…”

Section: Nmr Spectroscopymentioning

confidence: 99%

Magnetic resonance imaging (MRI) techniques for polymer electrolyte membrane and direct alcohol fuel cell characterization

Feindel

2012

Polymer Electrolyte Membrane and Direct Methanol Fuel Cell Technology

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The proton dynamics of imidazole methylphosphonate: an example of cooperative ionic conductivity

Cited by 25 publications

References 50 publications

Imidazolium methanesulfonate as a high temperature proton conductor

Imidazolium methanesulfonate as a high temperature proton conductor

Dynamics of benzimidazole ethylphosphonate: a solid-state NMR study of anhydrous composite proton-conducting electrolytes

Magnetic resonance imaging (MRI) techniques for polymer electrolyte membrane and direct alcohol fuel cell characterization

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