Mechanically Coupled Internal Coordinates of Ionomer Vibrational Modes

Webber, Matthew; Dimakis, Nicholas; Kumari, Dunesh; Fuccillo, M. K.; Smotkin, Eugene S.

doi:10.1021/ma100915u

Cited by 59 publications

(136 citation statements)

References 16 publications

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“…S1-2, 5, 7) reveal a pair of near degenerate normal modes that make up the 730 cm −1 band and another normal mode pair contributing to the 806 cm −1 band. While both observed bands are assigned by Peng et al 49 as "due to Teflon skeleton structure", the eigenvector animations enable a more detailed set of assignments.…”

Section: Resultsmentioning

confidence: 98%

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Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells

Kendrick

Fore

Doan

et al. 2016

J. Electrochem. Soc.

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Operando Raman micro-spectroscopy of the membrane electrode assembly (MEA) of a fully operating hydrogen/oxygen Nafion electrolyte fuel cell is described. Coarse depth profiling of the fuel cell system enabled appropriate positioning of the microspectroscopy laser focal point for MEA catalytic layer spectroscopy. An increase in the ionomer state-of-hydration, from oxygen reduction at the cathode, transitions ion exchange sites from the sulfonic acid to the dissociated sulfonate form. Visualization of density functional theory calculated normal mode eigenvector animations enabled assignments of Nafion side-chain vibrational bands in terms of the exchange site local symmetry: C 1 and C 3V modes correlate to the sulfonic acid and sulfonate forms respectively. The gradual transition of the MEA spectra from C 1 to C 3V modes, from the fuel cell open circuit voltage to the short circuit current respectively, demonstrate the utility of vibrational group mode assignments in terms of exchange site local symmetry.

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Section: Resultsmentioning

confidence: 98%

“…We reported that divalent ions in dehydrated Nafion bind with C 3V symmetry [48][49][50] to sulfonate oxygens. Hester and Krishnan confirmed C 3V binding of divalent metals to dry molten sulfonates.…”

Section: Resultsmentioning

confidence: 99%

Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells

Kendrick

Fore

Doan

et al. 2016

J. Electrochem. Soc.

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show abstract

“…Our previous state-of-hydration dependent spectroscopy combined with DFT normal mode analysis 4 resolved similar such controversies [24,[27][28][29][30] by (1) use of normal mode eigenvector animations for IR 5 band assignment of Nafion group modes and (2) categorization Nafion-[H] side-chain group modes in 6 terms of the exchange site local symmetry under fully hydrated (3-fold axis of symmetry) and dehydrat-7 ed conditions (absence of symmetry), [26,29] corresponding to C 3V and C 1 modes respectively. 8 Figure 1 shows the Nafion chemical repeat units, representing the hydrated (55-atom) and dehydrated 9…”

Section: Manuscriptmentioning

confidence: 95%

“…Eigenvector anima-1 tions of the 983* cm -1 peak confirm that the observed 969 cm -1 is primarily an SO 3 -symmetric stretch 2 that is mechanically coupled to COC-A asymmetric stretch. [26] 3…”

Section: Manuscriptmentioning

confidence: 99%

“…In addition, transitional 4 symmetries are also possible between C 3V and C 1 symmetries demarcated by threshold λ values of 4 and 5 10. [26] This coexistence of sulfonate and sulfonic acid forms of the exchange site must be considered 6 in any rigorous transport model. metal ions with a broad range of enthalpies of hydration [32] (∆H hyd ) and binding affinities.…”

Section: A N U S C R I P Tmentioning

confidence: 99%

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