Radiation Grafted Membranes for Polymer Electrolyte Fuel Cells 2020-01-09آ  Radiation Grafted...

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  • Radiation Grafted Membranes for Polymer Electrolyte Fuel Cells

    Habilitationsschrift

    zur Erlangung der Venia Legendi für das Fach Phyikalische Chemie

    eingereicht am

    Laboratorium für Physikalischen Chemie Departement Chemie und Angewandte Biowissenschaften

    Eidgenössische Technische Hochschule, Zürich

    vorgelegt von

    Lorenz Gubler

    geboren am 14. August 1971 von Grenchen, SO

    Zürich, 2016

  • „[…] we must resign ourselves to the condition that a hydrogen-oxygen battery is a potent

    destructive machine for any hydrocarbon based chemical.”

    - R.B. Hodgdon, J.R. Boyack, A.B. LaConti, TIS Report 65DE 5, General Electric

    Company, Lynn MA, USA, 1966

  • 5

    Acknowledgement

    The content of this work is based to a large extent on published articles and conference

    proceedings that were the outcome of research projects in the time frame of 2003 to 2014.

    Therefore, I am deeply grateful to the following PhD students who contributed significantly to the

    conceptual work and performed the lion’s share of experiments as well as data analysis and

    interpretation: Michal Slaski, Frank Wallasch, Hicham Ben youcef, Mini Mol Menamparambath,

    Sindy Dockheer, Kaewta Jetsrisuparb, Zhuoxiang Zhang, and Yves Buchmüller.

    Lukas Bonorand enriched the group with his industrial expertise and contributed significantly to

    making radiation grafted membranes attractive from a performance and durability point of view.

    Dr. Selmiye Alkan-Gürsel, as a postdoctoral fellow and supervisor of Michal Slaski and Hicham

    Ben youcef, performed essential studies on the synthesis and characterization of ETFE based

    grafted membranes. Dr. Dirk Henkensmeier and Dr. Hicham Ben youcef, during their engagement

    within the framework of an industrial project, carried out initial studies on the combination of

    styrene and nitrile comonomers.

    A fruitful collaboration with Prof. Willem H. Koppenol (ETH Zürich) on the topic of radical

    induced degradation of styrene type polyelectrolytes led to the publication of a number of key

    articles.

    I wish to thank Dr. Günther G. Scherer as head of the Fuel Cell research group and

    Electrochemistry Laboratory for his trust and support over the years until his retirement 2012, and

    Prof. Thomas J. Schmidt for his guidance and leadership from then onwards and his accepting to

    support this thesis to be submitted to the Department of Chemistry and Applied Biosciences

    (D-CHAB) of ETH Zürich. I thank Prof. Alexander Wokaun, head of the General Energy

    Research Department of PSI, for the many fruitful discussions on the PhD theses he supervised.

    I am furthermore indebted to a number of students who contributed to the studies presented here:

    Martin Schisslbauer, Adrian Weibel, Friederike Lindner, Benjamin Miserere, Regina Hafner, and

    Raphaël Chattot.

    Furthermore, I whish to thank the senior members of the Electrochemistry Laboratory, Dr. Pierre

    Boillat, Dr. Felix N. Büchi, Dr. Rüdiger Kötz, Prof. Petr Novák, for many discussions, advice in

    all matters of project management and administration, and fruitful collaborations.

  • 6

    Manuel Arcaro, Christian Marmy and Jürg Thut are gratefully acknowledged for their technical

    support and dedicated attitude to constantly improve the experimental environment and user

    friendliness of equipment and software. In particular, Jürg Thut contributed a great many ideas

    and solutions to cell hardware, laboratory and fuel cell test environment.

    I owe special thanks to the administrative team at PSI, in particular Isabella Kalt, Cordelia Gloor,

    Tanja Hogg, Esther Schmid and Solveig Wittke, for making bureaucratic processes as smooth as

    possible and sometimes invisible, rendering project management efficient and task oriented.

    I would furthermore like to express my gratitude to all the members of the Electrochemistry

    Laboratory and the former ‘Fuel Cell’ research group, now ‘Membranes & Electrochemical Cells’

    group, at PSI for the pleasant working atmosphere and fruitful discussions.

    The research leading to the results presented in this work was funded and supported by the

    following industrial partners and institutions: Conception et Développement Michelin (Givisiez

    FR), Belenos Clean Power Holding (Marin NE), Swiss Federal Office of Energy, Swiss National

    Science Foundation, ETH Zürich, and Paul Scherrer Institut.

    I finally wish to thank my wife Xun for her boundless support, infinite patience, profound

    friendship and love. I would also like to thank our daughters Céleste and Stella for their patience,

    having seen much less of their father than they deserve.

    June, 2016 Lorenz Gubler

  • 7

    Table of Contents

    Synopsis 9

    Introduction 11

    0-1 A Historical Perspective 12

    0-2 Fuel Cells in the Context of Renewable Energy Scenarios 22

    0-2 Motivation 38

    0-3 Structure of the Thesis 39

    I Polymer Design Aspects of Radiation Grafted Membranes for Fuel Cells 41

    1-2 Review of Existing Literature 42

    1-3 Base Film Requirements 50

    1-4 Choice of Grafting Monomer(s) 63

    1-5 Current Status 81

    II Experimental Methods 91

    2-1 Membrane Synthesis and Characterization 92

    2-2 Composition Analysis of Co-grafted Membranes 109

    2-3 Pulse Radiolysis 121

    III Multi-Monomer Grafted Membranes 125

    3-1 Introduction 126

    3-2 AMS-MAN Co-grafted Membranes 136

    3-3 S-MAN and S-AN Co-grafted Membranes 159

    3-4 Membranes with Polymer-Bound Antioxidants 177

    3-5 Conclusion 196

    IV Mechanisms of Chemical Degradation 199

    4-1 Introduction 200

    4-2 Radical-Induced Membrane Degradation 204

    4-3 Studies of Radical Attack on Oligomer Model Systems 218

    4-4 Accelerated Aging Tests of Fuel Cell Membranes 238

    4-5 Conclusion 257

  • 8

    Conclusions & Prospects 259

    References 263

    Curriculum Vitae 293

  • 9

    Synopsis

    Electrochemical energy conversion and storage technologies play a key role in future energy and

    mobility scenarios. Fuel cells offer the prospect of clean and efficient electricity generation for a

    variety of applications, such as stationary power systems and electric vehicles. The commercial

    competitiveness strongly depends on the performance, reliability, durability and cost of fuel cell

    systems. The development of cost-efficient ion-conducting membranes for the polymer electrolyte

    fuel cell (PEFC) with designed architecture and functional properties can contribute to bringing

    technology forward in this direction.

    The modification of a pre-existing polymer film via radiation induced graft copolymerization

    (“radiation grafting”) is a versatile and potentially low cost method to introduce desired properties

    into the material, such as ion conductivity. Compared to commonly used perfluoroalkylsulfonic

    acid (PFSA) membranes, such as Nafion®, in fuel cells, radiation grafted proton conducting

    membranes can be prepared using cheap base polymers and commercially available grafting

    monomers. The challenges herein are mainly associated with achieving concurrently performance

    and durability attributes competitive to those of PFSA membranes.

    This work focuses on the polymer design aspects and understanding of chemical degradation

    phenomena of radiation grafted proton conducting membranes for fuel cells. A brief historical

    outline and extensive review of developments in radiation grafted membranes over the past decade

    aims at placing this study into the context of the technological state-of-the-art. The central topics

    of membrane development are the use of α-methylstyrene and nitrile comonomers as graft

    component to improve chemical stability. Moreover, polymer-bound antioxidants are introduced

    to this end. The study of membrane degradation mechanisms is based, on the one hand, on pulse

    radiolysis studies of oligomer model compounds to study mechanisms of radical induced polymer

    breakdown. On the other hand, single cell tests under accelerated degradation conditions

    combined with qualitative and quantitative membrane characterization techniques are invaluable

    tools to develop an understanding of membrane aging phenomena.

    The studies presented here highlight that radiation grafted fuel cell membranes, if properly

    designed, can compare favorably with PFSA membranes in terms of performance and durability.

    Process development and scale-up of membrane fabrication are among the grand challenges of the

    future, which is beyond the scope of academic research and requires industrial involvement.

  • Introduction

    1 A Historical Perspective 12

    1.1 Early Hydrocarbon Based Membranes 12 1.2 Fluorinated Membranes 13 1.3 Perfluoroalkylsulfonic Acid (PFSA) Membranes 14 1.4 Early Radiation Grafted Membranes 16 1.5 Industrial Development Efforts 18 1.6 Fuel Cell Development Takes Off 20

    2 Fuel Cells in the Context