Hydrocarbon Proton Exchange Membranes

Gubler, Lorenz; Koppenol, Willem H.

doi:10.1002/9781119196082.ch5

Cited by 9 publications

(16 citation statements)

References 89 publications

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“…The final result of HO attack may be chain oxidation (e.g., hydroxylation), crosslinking, or chain fragmentation. 5 These different mechanisms of polymer aging depend on the chemistry of the polymer. Thus, strategies to prevent aging ought to take these pathways into account ( Fig.…”

Section: Introductionmentioning

confidence: 99%

“…11 Radical scavenging by Ce 3+ is very effective in PFSA membranes, because the lifetime of HO is on the order of microseconds, thus with a relatively small concentration of Ce 3+ of B0.1 M over 90% of HO are quenched. 5 The ratio of Ce 4+ to Ce 3+ is influenced by the chemistry of the medium. For example, H 2 O 2 and HO 2 , which are also present in a fuel cell membrane, 12…”

Section: Introductionmentioning

confidence: 99%

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Attack of hydroxyl radicals to α-methyl-styrene sulfonate polymers and cerium-mediated repair via radical cations

Nolte

Nauser

Gubler

2020

Phys. Chem. Chem. Phys.

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Both synthetic polymers (membranes, coatings, packaging) and natural polymers (DNA, proteins) are subject to radical-initiated degradation. In order to mitigate the deterioration of the polymer properties, antioxidant strategies need to be devised. We studied the reactions of poly(a-methylstyrene sulfonate), a model compound for fuel cell membrane materials, with different degrees of polymerization with OH radicals as well as subsequent reactions. We observed the resulting OH -adducts to react with oxygen and eliminate H 2 O, the relative likelihood of which is determined by pH and molecular weight. The resulting radical cations can be reduced back to the parent molecule by cerium(III). This 'repair' reaction is also dependent on molecular weight likely because of intramolecular stabilization. The results from this study provide a starting point for the development of new hydrocarbon-based ionomer materials for fuel cells that are more resistant to radical induced degradation through the detoxification of intermediates via damage transfer and repair pathways. Furthermore, a more fundamental understanding of the mechanisms behind conventional antioxidants in medicine, such as ceria nanoparticles, is achieved.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Attack of hydroxyl radicals to α-methyl-styrene sulfonate polymers and cerium-mediated repair via radical cations

Nolte

Nauser

Gubler

2020

Phys. Chem. Chem. Phys.

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“…To improve the chemical stability of membrane ionomers, it is important to understand the radical attack and chemical degradation mechanism of hydrocarbon-based membranes (for detailed studies, see Holmes et al [26] or Gubler et al [124,137] ).…”

Section: Chemical Stabilitymentioning

confidence: 99%

“…Two common approaches to improve the chemical stability of membranes are doping the membrane with 1) phenolic compounds, e.g., pyridine [19] or 2) cerium ions (Ce 3+ ) and oxides thereof. [137] Cerium is still considered the most effective radical scavenger known in PFSA-based fuel cells, thanks to the ability to regenerate by redox cycling between Ce 3+ and Ce 4+ in the presence of H 2 O 2 . [138] Despite the lower scavenging rate of Ce 3+ (10 8 m −1 s −1 ) compared to the attack rate of radicals on the aromatic compounds (10 9 -10 10 m −1 s −1 ) (all values determined in aqueous solutions and ambient temperature), [139] some studies [49,140] observed positive effects of cerium-based additives on the chemical stability of the hydrocarbon-based membrane.…”

Section: Chemical Stabilitymentioning

confidence: 99%

Fully Hydrocarbon Membrane Electrode Assemblies for Proton Exchange Membrane Fuel Cells and Electrolyzers: An Engineering Perspective

Nguyen

Klose

Metzler

et al. 2022

Advanced Energy Materials

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“…around 1 ns, which prevents effective scavenging by cerium-ions at practical concentrations. 28 Under these circumstances, and in analogy to biology, antioxidant action cannot be based on damage prevention but must focus instead on repair and inhibition of damage propagation. 31 This may be possible if intermediates formed upon radical attack are sufficiently long-lived.…”

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confidence: 99%

Possible Repair Mechanism for Hydrocarbon-Based Ionomers Following Damage by Radical Attack

Wild

Németh

Nolte

et al. 2021

J. Electrochem. Soc.

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Polymer electrolyte fuel cell (PEFC) membranes are subject to radical-induced degradation. Antioxidant strategies for hydrocarbon-based ionomers containing aromatic units can focus on intermediates that are formed upon attack by hydroxyl radicals (HO • ). Among the different intermediates, the cation radical P •+ is the most promising target for repair, for example by cerium(III). For the "repair" reaction of Ce(III) with radicals of a poly(α-methylstyrene sulfonate) oligomer we determined an activation energy of (9 ± 2) kJ mol −1 and a rate constant of 1.6 • 10 8 M −1 s −1 at 80°C by pulse-radiolysis. For the reduction of Ce(IV) by hydrogen peroxide the activation energy was determined by stopped-flow as (30 ± 1) kJ mol −1 with a rate constant of 4.8 • 10 6 M −1 s −1 at 80°C. These parameters are fed into a kinetics model to estimate the efficacy of the cerium (III)/(IV) redox couple as a catalytic repair agent in hydrocarbon-based fuel cell membranes. While cerium can mitigate polymer degradation, repair efficacy depends on the polymer degradation pathway and the nature and lifetime of the intermediates.

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Hydrocarbon Proton Exchange Membranes

Cited by 9 publications

References 89 publications

Attack of hydroxyl radicals to α-methyl-styrene sulfonate polymers and cerium-mediated repair via radical cations

Attack of hydroxyl radicals to α-methyl-styrene sulfonate polymers and cerium-mediated repair via radical cations

Fully Hydrocarbon Membrane Electrode Assemblies for Proton Exchange Membrane Fuel Cells and Electrolyzers: An Engineering Perspective

Possible Repair Mechanism for Hydrocarbon-Based Ionomers Following Damage by Radical Attack

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