In-situ spin trap electron paramagnetic resonance study of fuel cell processes

Panchenko, Alexander; Dilger, Herbert; Kerres, Jochen; Hein, M.; Ullrich, A.; Kaz, Till; Roduner, Emil

doi:10.1039/b404253k

Cited by 153 publications

(132 citation statements)

References 20 publications

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“…3 x10 -4 M). In addition to hydrogen peroxide, the very aggressive hydroxyl -situ ESR spin trapping techniques (18)(19). Due to the facile reaction betwee 2 O 2 (eq 1 be present.…”

Section: Fuel Cell Oxidantsmentioning

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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“…3 x10 -4 M). In addition to hydrogen peroxide, the very aggressive hydroxyl -situ ESR spin trapping techniques (18)(19). Due to the facile reaction betwee 2 O 2 (eq 1 be present.…”

Section: Fuel Cell Oxidantsmentioning

confidence: 99%

The Chemistry of Fuel Cell Membrane Chemical Degradation

2008

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“…Thus, we observed recently OH radicals during fuel cell operation in the formed water by means of the spintrapping technique. 72 The results presented in this paper were obtained for UHV conditions, but when one studies electrochemical reactions, the electrode is in contact with liquid water, and under fuel cell conditions the catalyst is covered with H 2 O molecules to large extent. Radical intermediates formed during oxygen reduction can change their properties significantly, they even leave the surface of an electrocatalyst in the presence of water 17,33 to recombine in bulk solution, or to participate in membrane degradation reactions.…”

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confidence: 99%

“…17 It is therefore of key interest to explore the energetics of reaction intermediates on Pt surfaces. How strongly do the radicals adsorb and under what conditions do they leave the surface of the Pt catalyst to deploy their destructive nature?…”

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confidence: 99%

Ab Initio Calculations of Intermediates of Oxygen Reduction on Low-Index Platinum Surfaces

Panchenko

Koper

Shubina

et al. 2004

J. Electrochem. Soc.

182

187

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Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Platinum catalysts are involved in a vast variety of redox reactions, and O 2 reduction is one of the most important of them. Therefore, considerable efforts are undertaken by electrochemists to understand the fundamental aspects of Pt catalysts and to improve the properties of applied catalytic systems in general. The fundamental relevance of Pt catalytic properties has become even more important because carbon-supported Pt catalysts have so far been the best choice for the oxygen reduction at the cathode of low-temperature polymer electrolyte membrane fuel cells ͑PEMFCs͒. 1The oxygen reduction reaction ͑ORR͒ on Pt surfaces has been widely studied in electrochemistry, but the details of the mechanism remain elusive. The overall ORR is a multistep process involving four electron transfers during which bonds are broken and formed. It is still not clear whether the process starts from the oxygen molecule dissociation on Pt electrodes, this being followed by electron and proton transfer, or whether the first reduction step happens before O-O bond cleavage. Damjanovic proposed that the first step is an electron transfer to the O 2 moleculeThis step is rate-determining and is either accompanied by or followed by a fast proton transfer. A theoretical study by Sidik et al. has proven the first electron transfer to be rate-determining on dual adsorption sites. Proton transfer is involved in this step, because the electron affinity of the reactant complex is increased significantly by t...

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“…It was therefore difficult to extract a strong causal relationship between fuel cell operating parameters, ROS generation rates, and ROS-induced chemical degradation. The presence of ROS in PEM fuel cells has been directly identified by electron paramagnetic resonance (EPR) measurements (21)(22)(23)(24). However, these measurements are limited to cells that fit within the EPR probe and cannot be translated to subscale or larger scale cells operating under realistic conditions.…”

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Investigation of polymer electrolyte membrane chemical degradation and degradation mitigation using in situ fluorescence spectroscopy

Prabhakaran

Arges

Ramani

2012

Proc. Natl. Acad. Sci. U.S.A.

144

126

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A fluorescent molecular probe, 6-carboxy fluorescein, was used in conjunction with in situ fluorescence spectroscopy to facilitate realtime monitoring of degradation inducing reactive oxygen species within the polymer electrolyte membrane (PEM) of an operating PEM fuel cell. The key requirements of suitable molecular probes for in situ monitoring of ROS are presented. The utility of using free radical scavengers such as CeO 2 nanoparticles to mitigate reactive oxygen species induced PEM degradation was demonstrated. The addition of CeO 2 to uncatalyzed membranes resulted in close to 100% capture of ROS generated in situ within the PEM for a period of about 7 h and the incorporation of CeO 2 into the catalyzed membrane provided an eightfold reduction in ROS generation rate.fuel cells | Nafion® degradation | hydroxyl radicals | hydroperoxyl radicals | miniature fluorescence probe H ydrogen/air (H 2 ∕air) polymer electrolyte membrane (PEM) fuel cells possess high efficiency and modularity. However, significant technical advances are required to facilitate fuel cells' commercialization and widespread use in targeted applications in the automotive, portable power, and military sectors. A key technological issue that remains to be addressed is component durability under an array of adverse operating conditions. The ionexchange membrane in a PEM fuel cell is one of the components whose limited long-term durability is of concern. The PEM undergoes mechanical, thermal, and chemical degradation during fuel cell operation (1-8). The chemical degradation process that takes place in a H 2 ∕O 2 PEM fuel cell is attributed to reactive oxygen species (ROS) that are generated in situ through both chemical and electrochemical pathways during fuel cell operation. Hydrogen peroxide (H 2 O 2 ) is an ROS and is often an intermediate formed in both pathways and is known to form free radical ROS in the presence of transition metal ions via the Fenton mechanism (9-12). These free radical ROS, namely hydroxyl and hydroperoxyl radicals, are amongst the strongest oxidizing agents known. ROS initiate oxidative degradation of both the PEM backbone and the side chains that contain ionic groups that are essential for ion conduction (13-16). The adverse consequences of these degradation modes (e.g., membrane thinning, pin-hole formation, and loss of ionic conductivity) eventually contribute to catastrophic cell and stack failure. Complete elimination of ROS generation and PEM chemical degradation, while a worthy goal, is difficult due to constraints in terms of membrane materials, choice of fuel and oxidant, and fuel cell operating conditions. Therefore, it is imperative to develop effective mitigation strategies that minimize the rate and extent of PEM degradation.Prior to proposing an effective mitigation strategy, it is essential to quantify the rate of ROS generation within the PEM during fuel cell operation. However, detecting the presence of ROS within the PEM of an operating fuel cell is an extremely difficult proposition because free ra...

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In-situ spin trap electron paramagnetic resonance study of fuel cell processes

Cited by 153 publications

References 20 publications

The Chemistry of Fuel Cell Membrane Chemical Degradation

The Chemistry of Fuel Cell Membrane Chemical Degradation

Ab Initio Calculations of Intermediates of Oxygen Reduction on Low-Index Platinum Surfaces

Investigation of polymer electrolyte membrane chemical degradation and degradation mitigation using in situ fluorescence spectroscopy

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