Radiation grafted fuel cell membranes based on co-grafting of α-methylstyrene and methacrylonitrile into a fluoropolymer base film

Gubler, Lorenz; Slaski, Michal; Wallasch, Frank; Wokaun, Alexander; Scherer, Günther G.

doi:10.1016/j.memsci.2009.04.031

Cited by 57 publications

(35 citation statements)

References 35 publications

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“…Therefore, membranes based on trifluorostyrene (TFS) (Refs. 93 and 110) and a-methylstyrene (AMS), 111 which have a protected a-position, show superior chemical stability. Most of the HO reacts via addition to the SSA-ring, though.…”

Section: Discussionmentioning

confidence: 99%

Radical (HO_•, H_• and HOO_•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells

Gubler¹,

Dockheer²,

Koppenol³

2011

J. Electrochem. Soc.

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263

268

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Formation of radicals, such as HO , H and HOO , in the membrane of the polymer electrolyte fuel cell and their attack on perfluoroalkylsulfonic acid (PFSA) and poly(styrenesulfonic acid) (PSSA) ionomers was simulated based on a kinetic framework with H 2 O 2 as "parent" molecule and with contaminating Fe as parameter. Analysis under quasi-steady state conditions yielded radical concentrations of around 10 À19 M for H , 10 À16 M for HO and 10 À10 M for HOO . H is formed via the reaction of HO with H 2 dissolved in the membrane. The attack of the PFSA ionomer was assumed to proceed via weak carboxylic end-groups. The corresponding calculated fluoride emission rate (FER) showed good agreement with experimental data under ex situ Fenton test conditions. The predicted FER under fuel cell operating conditions was underestimated by 2-3 orders of magnitude. It is likely that degradation via side-chain attack is prevalent during open circuit voltage hold tests. The oxidative degradation of PSSA ionomer follows an entirely different pathway, because, in addition to a-hydrogen abstraction by HO , the aromatic ring effectively scavenges HO to form an OH-adduct. Follow-up reactions lead to chain scission and formation of a stable hydroxylated degradation product.The proton conducting membrane in the polymer electrolyte fuel cell (PEFC) is exposed to considerable oxidative stress due to the presence of reactive intermediates formed in the membrane electrode assembly (MEA), which attack the electrolyte membrane and lead to chain scission, loss of polymer constituents, membrane thinning and, eventually, failure of the cell. 1,2 The chemical breakdown of the polymer additionally causes loss of mechanical integrity with ensuing mechanical failure of the membrane due to pinhole or crack formation. 3 The nature of the reactive intermediates formed during electrochemical H 2 and O 2 conversion in the PEFC has been discussed for many years in many articles. The insight that H 2 O 2 is involved in membrane degradation was already gained in the 1960s. 4,5 The observation that iron or other redox-active metal ions appeared to accelerate the degradation led to the suggestion that oxygen radicals are produced through the metal-ion-catalyzed decomposition of hydrogen peroxide (Fenton reaction). The working hypothesis that hydroxyl radicals (HO ) and hydroperoxyl radicals (HOO ) are the responsible species for membrane degradation has been accepted for a long time. Direct detection of radical intermediates in fuel cells was accomplished only recently by introducing spin-trapping agents into the MEA and placing a miniature fuel cell into an electron spin resonance (ESR) spectrometer. Using this approach, Roduner et al. proposed that HO and polymer derived carbon centered radicals are formed. 6 More recently, Schlick et al., using a similar approach, proved the presence of carbon centered radicals, HO , HOO as well as H in an operating fuel cell. 7 The reaction mechanisms leading to the formation of radical intermediates have been the subject ...

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Section: Discussionmentioning

confidence: 99%

Radical (HO_•, H_• and HOO_•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells

Gubler¹,

Dockheer²,

Koppenol³

2011

J. Electrochem. Soc.

Self Cite

263

268

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“…Indeed, the toughness of the ETFE-based grafted film and membrane decreases drastically with the increase of the GL and the crosslinker concentration. Furthermore, the ETFE film shows a satisfactory mechanical stability at relatively high doses (50 kGy), which provides the opportunity to use it with other monomer systems, which suffer from poor grafting kinetics, such as, a-methylstyrene/ methacrylonitrile monomer combination [34].…”

Section: Resultsmentioning

confidence: 99%

Influence of Radiation‐Induced Grafting Process on Mechanical Properties of ETFE‐Based Membranes for Fuel Cells

et al. 2010

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The mechanical stability is, in addition to thermal and chemical stability, a primary requirement of polymer electrolyte membranes in fuel cells. In this study, the impact of grafting parameters and preparation steps on stress–strain properties of ETFE‐based proton conducting membranes, prepared by radiation‐induced grafting and subsequent sulphonation, was studied. No significant change in the mechanical properties of the ETFE base film was observed below an irradiation dose of 50 kGy. It was shown that the elongation at break decreases with increasing both the crosslinker concentration and graft level (GL). However, the tensile strength was positively affected by the crosslinker concentration. Yield strength and modulus of elasticity are almost unaffected by the introduction of crosslinker. Interestingly, yield strength and modulus of elasticity increase gradually with GL without noticeable change of the inherent crystallinity of grafted films. The most brittle membranes are obtained via the combination of high GL and crosslinker concentration. The optimised ETFE‐based membrane (GL of ∼25%, 5% DVB v/v), shows mechanical properties superior to those of Nafion® 112 membrane. The obtained results were correlated qualitatively to the other ex situ properties, including crystallinity, thermal properties and water uptake of the grafted membranes.

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“…Preparation of proton-exchange membranes for fuel cells by radiation-induced grafting of AMS and MAN onto FEP films in presence of divinylbenzene (DVB) or diisopropenylbenzene (DIPB) as a crosslinking agent was reported [109,110]. A schematic representation for preparation of radiation-grafted membranes based on AMS by co-grafting with MAN and subsequent sulfonation is shown in Figure 16.…”

Section: Figure 16mentioning

confidence: 99%

Radiation-grafted materials for energy conversion and energy storage applications

Nasef

Gürsel

Karabelli

et al. 2016

Progress in Polymer Science

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Radiation grafted fuel cell membranes based on co-grafting of α-methylstyrene and methacrylonitrile into a fluoropolymer base film

Cited by 57 publications

References 35 publications

Radical (HO_•, H_• and HOO_•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells

Radical (HO_•, H_• and HOO_•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells

Influence of Radiation‐Induced Grafting Process on Mechanical Properties of ETFE‐Based Membranes for Fuel Cells

Radiation-grafted materials for energy conversion and energy storage applications

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Radiation grafted fuel cell membranes based on co-grafting of α-methylstyrene and methacrylonitrile into a fluoropolymer base film

Cited by 57 publications

References 35 publications

Radical (HO•, H• and HOO•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells

Radical (HO•, H• and HOO•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells

Influence of Radiation‐Induced Grafting Process on Mechanical Properties of ETFE‐Based Membranes for Fuel Cells

Radiation-grafted materials for energy conversion and energy storage applications

Contact Info

Product

Resources

About

Radical (HO_•, H_• and HOO_•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells

Radical (HO_•, H_• and HOO_•) Formation and Ionomer Degradation in Polymer Electrolyte Fuel Cells