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Antioxidant strategies for the stabilization of fuel cell membranes against oxidative stress

English title Antioxidant strategies for the stabilization of fuel cell membranes against oxidative stress
Applicant Gubler Lorenz
Number 132382
Funding scheme Project funding (Div. I-III)
Research institution Labor für Elektrochemie Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Material Sciences
Start/End 01.10.2010 - 31.03.2014
Approved amount 205'367.00
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All Disciplines (2)

Discipline
Material Sciences
Organic Chemistry

Keywords (6)

Radiation induced grafting; Reactive oxygen species; Antioxidant; Fuel cell; Radical scavenger; Proton exchange membrane

Lay Summary (German)

Lead
Brennstoffzellen erzeugen auf elektrochemischem Wege Strom aus Wasserstoff und Sauerstoff. Der oxidative Angriff der Elektrolytmembran durch radikalische Zwischenprodukte limitiert deren Lebensdauer. Das Forschungsvorhaben hat zum Ziel, Antioxidantien in die Polymerstruktur der Membran einzubringen. Die Alterungsmechanismen und Lösungsansätze weisen Parallelen zu biologischen Systemen auf, bei welchen die Natur ausgeklügelte Strategien entwickelt hat, um Radikale unschädlich zu machen.
Lay summary
Brennstoffzellen produzieren auf saubere und effiziente Art und Weise Strom. Die Polymerelektrolyt Brennstoffzelle mit einer Betriebstemperatur von rund 80°C eignet sich insbesondere für Anwendungen, wo hohe Leistungsdichte, Schnellstart und ein dynamischer Betrieb gefordert sind, z.B. in elektrischen Fahrzeugen und unterbruchsfreien Stromversorgungen. Poröse Elektroden auf Basis von Kohlenstofffasern und eine Ionen leitende Polymerelektrolyt-Membran stellen die elektrochemischen Kernkomponenten dieser Art Brennstoffzelle dar. Die Membran enthält Säuregruppen, die am Polymergerüst angebracht sind und die Leitfähigkeit ermöglichen. Die Verbesserung der Widerstandsfähigkeit der Membran gegenüber reaktiven Zwischenprodukten, welche während des Betriebes in der Zelle gebildet werden, ist ein zentraler Aspekt der Materialforschung und –entwicklung. Bei den Zwischenprodukten handelt es sich um Radikale. Im Rahmen dieses Projektes planen wir, Antioxidantien in die Membran einzubringen, welche die Membran vor dem radikalischen Angriff schützen sollen. Die Antioxidantien sollen dabei chemisch ans Polymergerüst angebunden werden, um nicht im Betrieb ausgewaschen zu werden. In Frage kommen hier beispielsweise Vitamin E oder artverwandte Verbindungen. Die gewählten Strategien zur chemischen Stabilisierung des Membran-Polymeren weisen Ähnlichkeiten auf zu Prozessen in lebenden Zellen. Auch hier entstehen bei Elektronenübertragungsprozessen Radikale. Diese werden durch ein komplexes System aus Antioxidantien und Enzymen unschädlich gemacht. Diese Analogien könnten nützlich sein, um oxidative Alterung in Brennstoffzellen-Membranen zu bekämpfen.
Direct link to Lay Summary Last update: 26.11.2012

Lay Summary (English)

Lead
Fuel cells generate electricity by virtue of electrochemical conversion of hydrogen and oxygen. Oxidative attack of the electrolyte membrane of the fuel cell is one of the factors limiting its lifetime. We aim to incorporate antioxidants into the polymer structure of the membrane. The aging mechanisms and approaches taken bear resemblance to the phenomena found in biology, where nature has devised cunning antioxidant strategies to deal with reactive oxygen species, such as superoxide (O2•-).
Lay summary
Fuel cells are energy conversion devices that produce electrical power based on an electrochemical reaction of a fuel, such as hydrogen, and an oxidant, typically oxygen taken from the ambient air. Among the different fuel cell types, the polymer electrolyte fuel cell (PEFC) is of particular interest for applications that require a high power density, rapid start-up, and a dynamic operation profile, for instance electric cars and backup power systems. In the PEFC, the fuel and air electrode are separated by a solid polymer membrane that serves as an electrolyte. In the hydrated state, the polymer ('ionomer') allows the transport of protons from the anode to the cathode of the cell. The materials typically used are perfluorinated polymers containing sulfonic acid groups. There is, however, a great interest to develop membranes that are more cost-effective. At the Paul Scherrer Institut (PSI), we have many years of experience in the preparation of proton conducting polymers for fuel cells by the radiation induced grafting method. The chemical stability of fuel cell membranes represents a major challenge. During fuel cell operation, reactive oxygen species (ROS) are created as intermediates. They can attack the ionomer and cause degradation and aging, eventually leading to the failure of the cell. The aim of this project is to incorporate antioxidant functionalities into the membrane to protect the polymer from oxidative degradation. Antioxidants and UV-light stabilizers are well-known additives in thermoplastics, yet incorporation of such materials in fuel cell membranes has so far not been considered. For the incorporation of antioxidants in proton conducting membranes, distinct circumstances regarding the conditions prevalent in the fuel cell will have to be taken into account, such as the elevated temperature of operation (~80°C), the presence of water and an acidic environment. Unlike in commodity thermoplatics, the fuel cell membrane is constantly bomarded with radicals. Therefore, the antioxidant functionalities have to be self-regenerative to continuously deactivate reactive species and thereby act as catalyst rather than a mere scavenger. This will be accomplished by a careful selection and evaluation of polymer functionalization and composite formation techniques. Furthermore, the antioxidants have to be tethered to the polymer backbone to prevent them from being leached out during fuel cell operation. This will require synthetic strategies, such as radiation grafting, to immobilize the functional antioxidant groups in the polymer matrix. The membranes thus prepared are expected to show improved resistance against oxidative aging.
Direct link to Lay Summary Last update: 26.11.2012

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Hydrocarbon Proton Exchange Membranes
Gubler Lorenz, Koppenol Willem H. (2017), Hydrocarbon Proton Exchange Membranes, in Schlick Shulamith (ed.), John Wiley & Sons, -, 107-138.
Antioxidants in non-perfluorinated fuel cell membranes: prospects and limitations
Buchmüller Yves, Zhang Zhuoxiang, Wokaun Alexander, Gubler Lorenz, Antioxidants in non-perfluorinated fuel cell membranes: prospects and limitations, in RSC Advances, 4, 51911-51915.
From Electrochemical Interface to Interphase (2D->3D) on Ionomer Membranes
Buchmüller Yves, Hafner Regina, Wokaun Alexander, Schmidt Thomas J., Gubler Lorenz, From Electrochemical Interface to Interphase (2D->3D) on Ionomer Membranes, in ChemElectroChem, 2, 338-342.
Fuel CellMembranes Based on Grafted and Post-Sulfonated Glycidyl Methacrylate (GMA)
Buchmüller Yves, Wokaun Alexander, Gubler Lorenz, Fuel CellMembranes Based on Grafted and Post-Sulfonated Glycidyl Methacrylate (GMA), in Fuel Cells, 13(6), 1177-1185.
Mass spectrometry to quantify and compare the gas barrier properties of radiation grafted membranes and Nafion(R)
Zhuoxiang Zhang, Raphaël Chattot, Lukas Bonorand, Kaewta Jetsrisuparb, Yves Buchmüller, Alexander Wokaun, Lorenz Gubler, Mass spectrometry to quantify and compare the gas barrier properties of radiation grafted membranes and Nafion(R), in Journal of Membrane Science, 472, 55-66.
Polymer-bound Antioxidants in Grafted Membranes for Fuel Cells
Buchmüller Yves, Wokaun Alexander, Gubler Lorenz, Polymer-bound Antioxidants in Grafted Membranes for Fuel Cells, in Journal of Materials Chemistry A, 2(16), 5870-5882.

Collaboration

Group / person Country
Types of collaboration
ETH Zürich, Institute of Inorganic Chemistry (Prof. Koppenol) Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
Université de Savoie, Le Bourget-du-Lac France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Ionizing Radiation and Polymers (IRaP) 2014 Talk given at a conference Radiation Grafted Fuel Cell Membranes: Radical Attack and Mitigation using Polymer-bound Antioxidants 05.10.2014 JeJu Island, Korean Republic (South Korea) Gubler Lorenz;
Fuel Cells 2014 Science & Technology - A Grove Fuel Cell Event Talk given at a conference Polymer-bound antioxidants in grafted membranes for fuel cells 03.04.2014 Amsterdam, Netherlands Buchmüller Yves;
5th International Conference on Fundamentals & Development of Fuel Cells (FDFC) Poster In-situ Degradation Studies of Radiation Grafted Membranes doped with Antioxidants 16.04.2013 Karlsruhe, Germany Buchmüller Yves;
XIème Colloque de l’Association PolyRay Talk given at a conference Fuel cell membranes based on grafted and post-sulfonated GMA 11.04.2013 Rouen, France Buchmüller Yves;
10th Meeting of the Ionizing Radiation and Polymers Symposium (IRaP´2012) Poster Mechanistic studies on grafting of glycidyl methacrylate (GMA) and styrene onto poly(ethylene-alt-tetrafluoroethylene) (ETFE) 14.10.2012 Krakau, Poland Gubler Lorenz; Buchmüller Yves;
12th Tihany Symposium on Radiation Chemistry Poster Introduction of functionalizable groups via radiation grafting into polymer electrolyte membranes for fuel cells 27.08.2011 Zalakaros, Hungary Buchmüller Yves;


Communication with the public

Communication Title Media Place Year
Talks/events/exhibitions Energieforschung am PSI: Solartechnologie und Brennstoffzellen German-speaking Switzerland 2012

Awards

Title Year
Travel bursary (reimbursement of registration fee) for the Fuel Cells 2014 Science & Technology – A Grove Fuel Cell Event (Amsterdam, April 3-4, 2014). 2014
Top 5 Posters at Tihany Symposium on Radiation Chemistry 2011

Associated projects

Number Title Start Funding scheme
144292 Lithium conducting polymer electrolytes with polysulphide barrier properties 01.01.2013 Project funding (Div. I-III)
175493 Radical Attack, Antioxidants and Polymer Repair Chemistry in Hydrocarbon based Fuel Cell Membranes 01.01.2018 Project funding (Div. I-III)
143432 Synthesis and characterization of porous materials with patterned wettabillity for advanced fuel cell water management strategies 01.04.2013 Project funding (Div. I-III)

Abstract

The scientific vision of this project is the incorporation of regenerative antioxidant functional-ities into proton conducting membranes used in fuel cells to protect the ionomer against oxi-dative stress, which is caused by reactive oxygen species (ROS), such as HO• and HOO•, prevalent in the H2/O2 fuel cell as intermediates. Although the technology of the polymer electrolyte fuel cell (PEFC) has come a long way in the past two decades and reached prototype and pre-commercial level, the reliability and stability of the used components and materials are still insufficient for high-revenue markets, e.g. electric vehicle applications with highly dynamic operating conditions. It has been established that chemical degradation of fuel cell membranes is caused by oxygen radical species, which are formed in the fuel cell as a result of the interaction of H2, O2 and the Pt catalyst. Effective mitigation of oxidative stress is a key to improving chemical stability and membrane lifetime.The approach taken in this project is aimed at the incorporation of organic redox couples as antioxidant functionalities, which are introduced to the membrane via radiation induced graft copolymerization, a technique which we have optimized over the past years for the prepara-tion of fuel cell membranes. The antioxidant units are intended to react with the aggressive oxygen radicals to mitigate or prevent oxidative degradation. Due to the constant bombard-ment of the ionomer with ROS, it is essential that the antioxidant functionalities, once spent, be restored to their reduced state to act again as radical scavengers. This reduction reaction is envisioned to be driven by the reductive power of the fuel cell anode. For the electrochemi-cal reaction to be effective within the bulk of the ionomer membrane, the redox units buried within the membrane will be electrically ‘wired’ to the anode through the incorporation of a conductive polymer.In a further aspect of the work, the creation of spatially confined antioxidant regions (‘barrier’ layer) will be investigated via surface grafting. Characterization of the membranes will involve the analysis of composition, fuel cell relevant properties (e.g. proton conductivity), and chemical stability in ex situ tests as well as in situ evaluation in fuel cells using accelerated aging test protocols.
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