Comparative DFT study of non-fluorinated and perfluorinated alkyl and alkyl-peroxy radicals

Mitov, Svetlin; Panchenko, Alexander; Roduner, Emil

doi:10.1016/j.cplett.2004.12.070

Cited by 27 publications

(26 citation statements)

References 17 publications

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“…It can be suggested that CF groups were attacked by a radical, and this led to a quaternary carbon radical. This result is supported by the CF dissociation energies reported in Table V,47 which suggest that tertiary CF bonds were the less stable positions on the perfluorinated chain 2. This covalent reticulation implied less than 1% carbon and could not be solely responsible for the drastic changes in the thermal behavior.…”

Section: Resultssupporting

confidence: 56%

Changes in the chemical structure and properties of a perfluorosulfonated acid membrane induced by fuel‐cell operation

Bas¹,

Flandin²,

Danerol³

et al. 2010

J of Applied Polymer Sci

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Changes in a perfluorosulfonated acid polymer membrane in membrane electrode assemblies were studied after different times under stationary conditions in fuel cells. A large series of characterizations demonstrated changes in the morphology, mechanical behavior, and thermal stability upon aging. Overall, the membrane evolution could be mainly attributed to both chemical degradation and cationic contamination. The reduction in the membrane thickness, detected by scanning electron microscopy, was ascribed to a radical unzipping mechanism and polymer chain erosion after 900 h in service. An additional monotonic decrease in the number of C tertiary F groups was observed even at 400 h. In parallel, membranes were cation-contaminated, and this led to drastic changes in the thermal and mechanical properties in the first stage of fuel-cell operation. The pollution cations were shown to have Lewis acid strengths close to 0.25 and thus strongly interacted with sulfonate anions of the membrane. The kinetic dependence of these membrane modifications and the influence of the platinum band were also examined.

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Section: Resultssupporting

confidence: 56%

Changes in the chemical structure and properties of a perfluorosulfonated acid membrane induced by fuel‐cell operation

Bas¹,

Flandin²,

Danerol³

et al. 2010

J of Applied Polymer Sci

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“…The grafting reaction with ETFE is therefore expected to proceed over alkyl radicals, which have been previously formed by hydrogen abstraction by the peroxy groups in the swollen regions of the polymer. Based on bond dissociation energies, it is expected that detachment of molecular oxygen, favored by the gain of entropy, is the most likely process of peroxy to alkyl radical conversion for both FEP and polyethylene 23. The detachment of atomic oxygen is unlikely.…”

Section: Resultsmentioning

confidence: 99%

In situ electron spin resonance study of styrene grafting of electron irradiated fluoropolymer films for fuel cell membranes

Mitov

Hübner

Brack

et al. 2006

J Polym Sci B Polym Phys

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Three different electron beam irradiated fluoropolymers (ETFE, FEP, and PVDF) as well as their grafting reactions with styrene in different diluents were investigated by means of electron spin resonance (ESR). Depending on the atmosphere during irradiation, ESR spectra of peroxy and alkyl radicals were observed. Radical decay as a function of time and temperature was investigated in the presence and absence of solvent. Grafting levels and number of monomer units per chain were calculated for both types of radicals. Irradiation atmosphere, grafting temperature, and added solvent affect the morphology of the fluoropolymers, in particular the crystalline versus amorphous fractions and their swelling. They thus influence the rate at which the initial radicals at the polymer backbone are reached during the grafting process.

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“…In addition, aqueous solution studies indicate that room temperature hydrogen abstraction reactions by OH have rate constants between 10 6 10 10 M -1 s -1 . The absolute rates are largely governed by the strength of the breaking bond and hence, the rates correlate with reaction exot solution and are anticipated to occur during fuel cell operation, Table VIII shows that abstractions of fluorine by OH are, as pointed out by others (25), clearly unreasonable on thermodynamic grounds no matter the strength of the C-F bond. The reason for this is quite simple; the energy cost of breaking a C-F bond (105 -130 kcal/mol) far exceeds the energy gain via the formation of the new O-F bond of HOF (51 kcal/mol).…”

Section: Pfsa Chemical Degradationmentioning

confidence: 99%

The Chemistry of Fuel Cell Membrane Chemical Degradation

2008

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A detailed thermochemical and kinetic analysis of PFSA ionomers and the reactive oxygen species formed in an operating fuel cell is reported. The analysis reveals that hydroxyl radical is the only oxygen species capable of abstracting a hydrogen atom from carboxylic acid intermediates, thereby propagating the PFSA main chain unzipping process. Two chemically specific, main chain scission mechanisms are proposed. The first involves formation of sulfonyl radicals under dry conditions and the second invokes the action of hydrogen atoms formed from hydrogen gas and hydroxyl radical. The thermochemical analysis provides a strong basis from which to rationalize the results from a broad range of in-situ and ex-situ fuel cell degradation studies.

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Comparative DFT study of non-fluorinated and perfluorinated alkyl and alkyl-peroxy radicals

Cited by 27 publications

References 17 publications

Changes in the chemical structure and properties of a perfluorosulfonated acid membrane induced by fuel‐cell operation

Changes in the chemical structure and properties of a perfluorosulfonated acid membrane induced by fuel‐cell operation

In situ electron spin resonance study of styrene grafting of electron irradiated fluoropolymer films for fuel cell membranes

The Chemistry of Fuel Cell Membrane Chemical Degradation

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