The Chemistry of Membranes Used in Fuel Cells Degradation and Stabilization

Examines the important topic of fuel cell science by way of combining membrane design, chemical degradation mechanisms, and stabilization strategies

This book describes the mechanism of membrane degradation and stabilization, as well as the search for stable membranes that can be used in alkaline fuel cells. Arranged in ten chapters, the book presents detailed studies that can help readers understand the attack and degradation mechanisms of polymer membranes and mitigation strategies. Coverage starts from fundamentals and moves to different fuel cell membrane types and methods to profile and analyze them.

The Chemistry of Membranes Used in Fuel Cells: Degradation and Stabilization features chapters on: Fuel Cell Fundamentals: The Evolution of Fuel Cells and their Components; Degradation Mechanism of Perfluorinated Membranes; Ranking the Stability of Perfluorinated Membranes Used in Fuel Cells to Attack by Hydroxyl Radicals; Stabilization Mechanism of Perfluorinated Membranes by Ce(III) and Mn(II); Hydrocarbon Proton Exchange Membranes; Stabilization of Perfluorinated Membranes Using Nanoparticle Additives; Degradation Mechanism in Aquivion Perfluorinated Membranes and Stabilization Strategies; Anion Exchange Membrane Fuel Cells: Synthesis and Stability; In-depth Profiling of Degradation Processes in Nafion Due to Pt Dissolution and Migration into the Membrane; and Quantum Mechanical Calculations of the Degradation Mechanism in Perfluorinated Membranes.

• Brings together aspects of membrane design, chemical degradation mechanisms and stabilization strategies
• Emphasizes chemistry of fuel cells, which is underemphasized in other books
• Includes discussion of fuel cell performance and behavior, analytical profiling methods, and quantum mechanical calculations

The Chemistry of Membranes Used in Fuel Cells is an ideal book for polymer scientists, chemists, chemical engineers, electrochemists, material scientists, energy and electrical engineers, and physicists. It is also important for grad students studying advanced polymers and applications.

Shulamith Schlick, DSc, is a Professor of Physical and Polymer Chemistry in the Department of Chemistry and Biochemistry, University of Detroit Mercy. One of the foremost authorities in the field of polymer research, Dr. Schlick has held visiting professorships and appointments worldwide. Among her publications is the book Advanced ESR Methods in Polymer Research, published by Wiley in 2006.

Preface xiii

About the Editor xvii

List of Contributors xix

1 The Evolution of Fuel Cells and Their Components 1
Thomas A. Zawodzinski, Zhijiang Tang, and Nelly Cantillo

1.1 Overview: A Personal Perspective of Recent Developments 1

1.2 Basics of Fuel Cell Operation 3

1.3 Types of Fuel Cells 5

1.3.1 Phosphoric Acid Fuel Cell 5

1.3.2 Molten Carbonate Fuel Cell and Solid Oxide Fuel Cell 5

1.3.3 Proton Exchange Membranes Fuel Cell 6

1.3.4 Alkaline Fuel Cell 6

1.3.5 Solid Acid Fuel Cell 8

1.4 Low Temperature Fuel Cells: Components 8

1.4.1 Membranes in PEM Systems 9

1.4.2 Electrocatalysts in PEM Systems 11

1.4.2.1 Catalyst Layer Structure in PEM Systems 13

1.5 Summary 16

Acknowledgments 16

References 16

2 Degradation Mechanism of Perfluorinated Membranes 19
Marek Danilczuk, Shulamith Schlick, and Frank D. Coms

2.1 Introduction 19

2.2 Fluoride Release Rate 22

2.3 Nuclear Magnetic Resonance 26

2.4 Fourier Transform Infrared Spectroscopy 30

2.5 Electron Spin Resonance 37

2.5.1 Direct ESR Radical Detection in Perfluorinated Membranes 37

2.5.2 Spin Trapping ESR 40

2.5.3 In Situ ESR Fuel Cell 41

2.5.4 Chemical Reactions and Crossover Processes in a Fuel Cell 43

2.5.5 Effect of Membrane Thickness 46

2.6 Conclusions 49

Acknowledgments 51

References 51

3 Ranking the Stability of Perfluorinated Membranes to Attack by Hydroxyl Radicals 55
Marek Danilczuk and Shulamith Schlick

3.1 Introduction 55

3.2 The Chemical Stability of Perfluorinated Ionomers 57

3.3 Electron Spin Resonance Studies of PFSAs Exposed to Hydroxyl Radicals 61

3.3.1 Spin©\Trapping ESR 61

3.3.2 Competitive Kinetics: Perfluorinated Ionomers as Competitors for HO• Radicals 62

3.3.3 Ce(III) as Competitor 68

3.4 Conclusions 70

Acknowledgments 72

References 72

4 Stabilization of Perfluorinated Membranes Using Ce3+ and Mn2+ Redox Scavengers: Mechanisms and Applications 75
Frank D. Coms, Shulamith Schlick, and Marek Danilczuk

4.1 Introduction 75

4.2 Oxidant Chemistry 76

4.3 Degradation Mechanisms of PFSA 79

4.4 Mitigation of Chemical Degradation by Redox Quenchers 81

4.4.1 Mitigation Mechanisms of Ce3+ and Mn2+ 82

4.4.1.1 Cerium Mitigation and Chain Scission Processes 89

4.4.2 ESR Spin Trapping Studies 89

4.4.3 Oxidative Stress and Ce3+ Mitigation 91

4.4.3.1 MEA Design 96

4.4.4 Cerium Distribution and Migration 97

4.4.5 CeO2 Mitigation 100

4.4.6 Synergistic Mitigation Strategies 101

4.5 Conclusions 103

Acknowledgments 104

References 104

5 Hydrocarbon Proton Exchange Membranes 107
Lorenz Gubler and Willem H. Koppenol

5.1 Introduction 107

5.2 Radical Intermediates in Fuel Cells 108

5.3 Hydrocarbon Membranes 114

5.4 Chemical Stabilization by Antioxidants 119

5.4.1 Regenerative Radical Scavenging in PFSA Membranes 119

5.4.2 Hydrocarbon Membranes Doped with Organic Antioxidants 121

5.4.3 Polymer©\Bound Antioxidants 122

5.5 The Challenge of Regeneration 125

5.5.1 Learnings from Mother Nature 125

5.5.2 Approaches for the Fuel Cell 126

5.6 Concluding Remarks 133

References 134

6 Stabilization of Perfluorinated Membranes Using Nanoparticle Additives 139
Guanxiong Wang, Javier Parrondo, and Vijay Ramani

6.1 Nanoparticle Additives as a Stabilizer for Perfluorinated Membranes 139

6.2 CeO2 and Modified CeO2 Nanoparticles as FRSs 141

6.3 Platinum©\Supported Ceria as FRS 152

6.4 Manganese Oxide and Manganese Oxide Composite as FRSs 154

6.5 Metal Nanoparticles as FRSs 160

6.6 Experimental Techniques for the Detection of Free Radicals and Measurement of the Membrane Degradation Rates 163

6.6.1 Fluoride Emission Rate 163

6.6.2 Fluorescence Spectroscopy as a Tool for the Detection and Quantification of Free Radical Degradation in PEMs 163

6.7 Conclusions 164

Acknowledgments 165

References 166

7 Degradation Mechanisms in Aquivion® Perfluorinated Membranes and Stabilization Strategies 171
Vincenzo Arcella, Luca Merlo, and Alessandro Ghielmi

7.1 Introduction 171

7.2 Properties of SSC Ionomers 173

7.3 Properties of Aquivion® Ionomers 173

7.4 The Need for High Stability of PFSA Membranes 177

7.5 PFSA Membrane Degradation in Fuel Cell 177

7.6 Generation of Radical Species in the Fuel Cell Environment 178

7.7 Degradation Studies on Aquivion® Membranes 181

7.8 Stabilization Procedures on Aquivion® Membranes 185

7.9 Conclusions 190

References 190

8 Anion Exchange Membranes: Stability and Synthetic Approach 195
Dongwon Shin, Chulsung Bae, and Yu Seung Kim

8.1 Introduction 195

8.2 Chemical Degradation Mechanisms 196

8.2.1 Degradation of Cationic Groups 196

8.2.1.1 Alkyl Ammoniums 196

8.2.1.2 N©\Based Cyclic Cations 199

8.2.1.3 Other Cationic Groups 202

8.2.2 Degradation of Polymer Backbones 204

8.2.2.1 Polyolefins 205

8.2.2.2 Polyaromatics 205

8.2.2.3 Polyacrylates 207

8.2.2.4 Polybenzimidazoles 208

8.2.2.5 Perfluorinated Polymers 208

8.3 Synthetic Approaches 210

8.3.1 Polyolefins 210

8.3.1.1 Polyethylene and Polypropylene 211

8.3.1.2 Polystyrene 212

8.3.1.3 Others 215

8.3.2 Polyaromatics 217

8.3.2.1 Cationic©\Group©\Tethered Poly(arylene)s 217

8.3.2.2 Poly(arylene)©\Containing Cationic Polymer Backbones 219

8.3.2.3 Multication©\Tethered Poly(arylene)s 219

8.3.3 Other Polymers 221

8.3.3.1 Polybenzimidazoles 221

8.3.3.2 Polynorbornenes 223

8.3.3.3 Perfluorinated Polymers 224

8.4 Conclusions 225

Acknowledgments 225

References 226

9 Profiling of Membrane Degradation Processes in a Fuel Cell by 2D Spectral–Spatial FTIR 229
Shulamith Schlick and Marek Danilczuk

9.1 Introduction 229

9.2 Optical Images of Nafion® Cross Sections 231

9.3 Line Scan Maps of the Membranes 232

9.4 FTIR Spectra of Nafion® MEAs 232

9.5 Abstraction of a Fluorine Atom on a Carbon in the Nafion® Main Chain by H• 235

9.6 Conclusions 237

Acknowledgments 237

References 238

10 Quantum Mechanical Calculations of the Degradation in Perfluorinated Membranes Used in Fuel Cells 241
Ted H. Yu, Boris V. Merinov, and William A. Goddard III

10.1 Introduction 241

10.2 Computational Methods 244

10.3 Results and Discussion 244

10.3.1 Generation of Radicals 244

10.3.1.1 Hydroxyl Radicals 244

10.3.1.2 Hydrogen Radicals, H• 247

10.3.1.3 Hydroperoxyl Radicals, HOO• 249

10.3.2 Concentrated HO• Conditions versus Fuel Cell Conditions 249

10.3.3 Degradation under Concentrated HO• Conditions 249

10.3.3.1 R©¤CF2H Polymer Main Chain Defect Initiation 249

10.3.3.2 R©¤CF¨TCF2 Polymer Main Chain Defect Initiation 250

10.3.3.3 R©¤COOH Polymer Main Chain Defect Initiation 250

10.3.3.4 Propagating Polymer Main Chain Degradation 250

10.3.3.5 Side©\Chain Degradation 252

10.3.4 Degradation under Fuel Cell Conditions with Fuel Crossover 256

10.3.4.1 Polymer Main Chain End©\Group Initiation 256

10.3.4.2 Propagating Polymer Main Chain Degradation 256

10.3.4.3 Side©\Chain Degradation 257

10.3.5 Degradation under Fuel Cell Conditions without Crossover 259

10.3.5.1 Degradation at the Cathode without H2 Crossover 259

10.3.5.2 Degradation at the Anode without O2 Crossover 261

10.4 Summary 265

10.4.1 Concentrated HO• Conditions 265

10.4.2 Fuel Cell Conditions 265

10.4.2.1 Fuel Cell Conditions without Crossover at Cathode 266

10.4.2.2 Fuel Cell Conditions without Crossover at Anode 266

Acknowledgments 267

References 267

Index 271

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