Table of Contents
Preface v
Acknowledgements ix
1 Introduction to fuel cells and their membranes 1
1.1 Introduction to fuel cells: Brief history and basics 1
1.1.1 Polymer electrolyte membrane fuel cells: Workings and components 4
1.1.2 Components of polymer electrolyte membrane fuel cells 5
1.2 Polymer electrolyte membranes 6
1.2.1 Scope and role in polymer electrolyte membrane fuel cells 6
1.2.2 Brief historical overview and state-of-the-art 8
References 10
2 Proton-conduction membranes: Requirements, challenges and materials 13
2.1 Overview of membrane materials and concepts 13
2.2 Requirements and challenges 15
2.2.1 Water uptake and proton conduction 15
2.2.2 Relationship between proton conduction, water transport and water concentration gradient in polymer membranes 17
2.2.3 Challenges - ionic transport versus membrane thickness 19
2.2.4 Challenges specific to application of fuel cells 19
2.2.5 Specific challenges for membranes in proton- exchange membrane fuel cells 20
2.2.6 Specific challenges for membranes in direct methanol fuel cells 20
2.3 Types of polymer electrolyte membranes 21
2.3.1 Perfluorosulfonic acid membranes 21
2.3.2 Partially fluorinated 23
2.3.3 Sulfonated hydrocarbon 23
2.3.4 Acid-base complexes 24
2.3.5 Natural polymers 25
2.3.6 Composites 26
2.4 Non-polymeric membranes 33
2.4.1 Solid acid membranes 33
2.4.2 Carbon nanomaterials 34
References 34
3 Proton-conducting membranes: Preparation methods 39
3.1 Introduction 39
3.2 Solution casting 40
3.3 Electrospinning 42
3.4 Multilayer membrane systems 43
3.4.1 Dip coating 45
3.4.2 Hot pressing 46
3.4.3 Filtration 46
3.5 Other approaches and concepts 48
References 50
4 Methods used for membrane characterisation 53
4.1 Introduction 53
4.2 Ex Situ characterisation methods 53
4.2.1 Water uptake 54
4.2.2 Ion-exchange capacity 56
4.2.3 Gas permeability 58
4.2.4 Methanol permeation test 59
4.2.5 Chemical degradation and durability testing 61
4.2.6 Tensile test 65
4.2.7 Thermal stability and thermomechanical durability tests 67
4.3 In situ characterisation 68
4.3.1 Proton conductivity 68
4.3.1.1 Four-probe method 69
4.3.1.2 Two-probe method 70
4.3.2 Current-voltage polarisation studies 70
4.3.3 Electrochemical impedance spectroscopy 72
4.3.3.1 Use of electrochemical impedance spectrometry to study the effects of membrane thickness 75
4.3.4 Other in situ tests 76
References 76
5 Membranes in single-cell proton-exchange membrane fuel cells and stacks 79
5.1 Introduction 79
5.2 Combining in situ and physical characterisation methods: Water behaviour inside a membrane 80
5.2.1 Diffusion of water and polymer reorganisation in Nafion® 80
5.2.2 Water transport through the membrane 83
5.2.3 Water distribution inside the membrane 86
5.3 Combining in situ and physical characterisation methods: Membrane conductivity and the factors governing it 89
5.4 Combining in situ and physical characterisation methods: Gas permeation through Nafion® membranes 91
5.4.1 Gas permeation through water 93
5.5 Membrane inside the operating proton-exchange membrane fuel cells: influence of catalyst layer defects 97
5.6 Membranes in exceptional conditions (durability and degradation): Challenges under application and operation-specific conditions 102
5.6.1 Membranes in cold start-up systems and freeze/ thaw cycles 102
5.6.2 Open circuit conditions 104
5.6.3 Effects of vibrations 105
5.6.4 Aircraft applications: Climatic challenges 107
5.6.5 Transit bus application 108
5.7 Single-cell in situ testing of Nafion®-hybrid, other perfluorosulfonic acid and non-perfluorosulfonic acid membranes 111
5.7.1 In situ proton-exchange membrane fuel cells testing at low and variable relative humidity conditions 111
5.7.2 In situ direct methanol fuel cell testing of hybrid membranes 114
5.7.3 In situ intermediate- and high-temperature proton-exchange membrane fuel cell operation 117
References 122
6 Future trends in polymer electrolyte membranes 127
6.1 Introduction 127
6.2 Future trends towards next-generation membranes: Enhancing proton conduction, durability and minimising the dependence on humidification 127
6.3 Disposal and recycling of lonomers and other membranes 129
6.4 Conclusions 131
References 133
Abbreviations 137
Index 141
