Solid State Proton Conductors - Properties and Applications in Fuel Cells

Preface xi About the Editors xiii Contributing Authors xv 1 Introduction and Overview: Protons, the Nonconformist Ions 1 Maria Luisa Di Vona and Philippe Knauth 1.1 Brief History of the Field 2 1.2 Structure of This Book 2 References 4 2 Morphology and Structure of Solid Acids 5 Habib Ghobarkar, Philippe Knauth and Oliver Sch af 2.1 Introduction 5 2.1.1 Preparation Technique of Solid Acids 5 2.1.2 Imaging Technique with the Scanning Electron Microscope 6 2.2 Crystal Morphology and Structure of Solid Acids 8 2.2.1 Hydrohalic Acids 8 2.2.2 Main Group Element Oxoacids 10 2.2.3 Transition Metal Oxoacids 20 2.2.4 Carboxylic Acids 22 References 24 3 Diffusion in Solid Proton Conductors: Theoretical Aspects and Nuclear Magnetic Resonance Analysis 25 Maria Luisa Di Vona, Emanuela Sgreccia and Sebastiano Tosto 3.1 Fundamentals of Diffusion 25 3.1.1 Phenomenology of Diffusion 26 3.1.2 Solutions of the Diffusion Equation 35 3.1.3 Diffusion Coefficients and Proton Conduction 37 3.1.4 Measurement of the Diffusion Coefficient 38 3.2 Basic Principles of NMR 40 3.2.1 Description of the Main NMR Techniques Used in Measuring Diffusion Coefficients 42 3.3 Application of NMR Techniques 47 3.3.1 Polymeric Proton Conductors 47 3.3.2 Inorganic Proton Conductors 58 3.4 Liquid Water Visualization in Proton-Conducting Membranes by Nuclear Magnetic Resonance Imaging 62 3.5 Conclusions 66 References 67 4 Structure and Diffusivity in Proton-Conducting Membranes Studied by Quasielastic Neutron Scattering 71 Rolf Hempelmann 4.1 Survey 71 4.2 Diffusion in Solids and Liquids 73 4.3 Quasielastic Neutron Scattering: A Brief Introduction 76 4.4 Proton Diffusion in Membranes 82 4.4.1 Microstructure by Means of SAXS and SANS 82 4.4.2 Proton Conductivity and Water Diffusion 89 4.4.3 QENS Studies 90 4.5 Solid State Proton Conductors 95 4.5.1 Aliovalently Doped Perovskites 96 4.5.2 Hydrogen-Bonded Systems 101 4.6 Concluding Remarks 104 References 104 5 Broadband Dielectric Spectroscopy: A Powerful Tool for the Determination of Charge Transfer Mechanisms in Ion Conductors 109 Vito Di Noto, Guinevere A. Giffin, Keti Vezzu', Matteo Piga and Sandra Lavina 5.1 Basic Principles 110 5.1.1 The Interaction of Matter with Electromagnetic Fields: The Maxwell Equations 110 5.1.2 Electric Response in Terms of em doP, sm doP, and ZmdoP 111 5.2 Phenomenological Background of Electric Properties in a Time-Dependent Field 114 5.2.1 Polarization Events 114 5.3 Theory of Dielectric Relaxation 127 5.3.1 Dielectric Relaxation Modes of Macromolecular Systems 129 5.3.2 A General Equation for the Analysis in the Frequency Domain of s(o) and e(o) 132 5.4 Analysis of Electric Spectra 132 5.5 Broadband Dielectric Spectroscopy Measurement Techniques 141 5.5.1 Measurement Systems 142 5.5.2 Contacts 158 5.5.3 Calibration 165 5.5.4 Calibration in Parallel Plate Methods 165 5.5.5 Measurement Accuracy 172 5.6 Concluding Remarks 180 References 180 6 Mechanical and Dynamic Mechanical Analysis of Proton-Conducting Polymers 185 Jean-Franc?ois Chailan, Mustapha Khadhraoui and Philippe Knauth 6.1 Introduction 185 6.1.1 Molecular Configurations: The Morphology and Microstructure of Polymers 185 6.1.2 Molecular Motions 187 6.1.3 Glass Transition and Other Molecular Relaxations 188 6.2 Methodology of Uniaxial Tensile Tests 191 6.2.1 Elasticity and Young s Modulus E 192 6.2.2 Elasticity and Shear Modulus G 195 6.2.3 Elasticity and Cohesion Energy 196 6.3 Relaxation and Creep of Polymers 197 6.3.1 Stress Relaxation of Polymers 198 6.3.2 Creep of Polymers 199 6.4 Engineering Stress Strain Curves of Polymers 201 6.4.1 True Stress Strain Curve for Plastic Flow and Toughness of Polymers 203 6.4.2 Behavior of Composite Membranes 204 6.4.3 Behavior in the Glassy Regime 205 6.4.4 Influence of the Rate of Deformation 206 6.4.5 Effect of Temperature on Mechanical Properties 209 6.4.6 Thermal Strain 210 6.5 Stress Strain Tensile Tests of Proton-Conducting Ionomers 211 6.5.1 Influence of Heat Treatment and Cross-Linking 212 6.5.2 Behavior of Composites 214 6.5.3 Conclusions 215 6.6 Dynamic Mechanical Analysis (DMA) of Polymers 217 6.6.1 Principle of Measurement 217 6.6.2 Molecular Motions and Dynamic Mechanical Properties 218 6.6.3 Experimental Considerations: How Does the Instrument Work? 219 6.6.4 Parameters of Dynamic Mechanical Analysis 220 6.7 The DMA of Proton-Conducting Ionomers 222 6.7.1 Perfluorosulfonic Acid Ionomer Membranes 222 6.7.2 Nonfluorinated Membranes 225 6.7.3 Organic Inorganic Composite (or Hybrid) Membranes 230 Glossary 235 References 236 7 Ab Initio Modeling of Transport and Structure of Solid State Proton Conductors 241 Jeffrey K. Clark II and Stephen J. Paddison 7.1 Introduction 241 7.2 Theoretical Methods 244 7.2.1 Ab Initio Electronic Structure 244 7.2.2 Ab Initio Molecular Dynamics (AIMD) 248 7.2.3 Empirical Valence Bond (EVB) Models 249 7.3 Polymer Electrolyte Membranes 251 7.3.1 Local Microstructure 251 7.3.2 Proton Dissociation, Transfer, and Separation 258 7.4 Crystalline Proton Conductors and Oxides 279 7.4.1 Crystalline Proton Conductors 279 7.4.2 Oxides 284 7.5 Concluding Remarks 290 References 290 8 Perfluorinated Sulfonic Acids as Proton Conductor Membranes 295 Giulio Alberti, Riccardo Narducci and Maria Luisa Di Vona 8.1 Introduction on Polymer Electrolyte Membranes for Fuel Cells 295 8.2 General Properties of Polymer Electrolyte Membranes 296 8.2.1 Ion Exchange of Polymers Electrolytes in H p Form 297 8.3 Perfluorinated Membranes Containing Superacid SO3H Groups 303 8.3.1 Nafion Preparation 304 8.3.2 Nafion Morphology 304 8.3.3 Nafion Water Uptake in Liquid Water at Different Temperatures 306 8.3.4 Water-Vapor Sorption Isotherms of Nafion 307 8.3.5 Curves T/nc for Nafion 117 Membranes in H p Form 308 8.3.6 Water Uptake and Tensile Modulus of Nafion 311 8.3.7 Colligative Properties of Inner Proton Solutions in Nafion 313 8.3.8 Thermal Annealing of Nafion 315 8.3.9 MCPI Method 315 8.3.10 Proton Conductivity of Nafion 319 8.4 Some Information on Dow and on Recent AquivionIonomers 321 8.5 Instability of Proton Conductivity of Highly Hydrated PFSA Membranes 321 8.6 Composite Nafion Membranes 323 8.6.1 Silica-Filled Ionomer Membranes 323 8.6.2 Metal Oxide-Filled Nafion Membranes 324 8.6.3 Layered Zirconium Phosphate- and Zirconium Phosphonate-Filled Ionomer Membranes 324 8.6.4 Heteropolyacid-Filled Membranes 325 8.7 Some Final Remarks and Conclusions 326 References 327 9 Proton Conductivity of Aromatic Polymers 331 Baijun Liu and Michael D. Guiver 9.1 Introduction 331 9.2 Synthetic Strategies of the Various Acid-Functionalized Aromatic Polymers with Proton Transport Ability 332 9.2.1 Sulfonated Poly(arylene ether)s 332 9.2.2 Sulfonated Polyimides 341 9.2.3 Other Aromatic Polymers as PEMs 344 9.3 Approaches to Enhance Proton Conductivity 349 9.3.1 Nanophase-Separated Microstructures Containing Proton-Conducting Channels 349 9.3.2 Replacement of Ph-SO3H by CF2 SO3H 353 9.3.3 Synthesis of High-IEC PEMs 355 9.3.4 Composite Membranes 356 9.4 Balancing Proton Conductivity, Dimensional Stability, and Other Properties 358 9.5 Electrochemical Performance of Aromatic Polymers 361 9.5.1 PEMFC Performance 362 9.5.2 DMFC Performance 363 9.6 Summary 363 References 365 10 Inorganic Solid Proton Conductors 371 Philippe Knauth and Maria Luisa Di Vona 10.1 Fundamentals of Ionic Conduction in Inorganic Solids 371 10.1.1 Defect Concentrations 372 10.1.2 Defect Mobilities 373 10.1.3 Kr oger Vink Nomenclature 373 10.1.4 Ionic Conduction in the Bulk: Hopping Model 376 10.2 General Considerations on Inorganic Solid Proton Conductors 378 10.2.1 Classification of Solid Proton Conductors 379 10.3 Low-Dimensional Solid Proton Conductors: Layered and Porous Structures 381 10.3.1 b- and b00-Alumina-Type 381 10.3.2 Layered Metal Hydrogen Phosphates 382 10.3.3 Micro- and Mesoporous Structures 384 10.4 Three-Dimensional Solid Proton Conductors: Quasi-Liquid Structures 385 10.4.1 Solid Acids 385 10.4.2 Acid Salts 385 10.4.3 Amorphous and Gelled Oxides and Hydroxides 387 10.5 Three-Dimensional Solid Proton Conductors: Defect Mechanisms in Oxides 387 10.5.1 Perovskite-Type Oxides 388 10.5.2 Other Structure Types 393 10.6 Conclusion 394 References 395 Index 399