Modeling and Diagnostics of Polymer Electrolyte Fuel Cells (eBook)

Preface 6
Contents 8
List of Contributors, MAE 49 15
Modern Aspects of Electrochemistry 18
1 Durability of PEM Fuel Cell Membranes 19
1 Summary 19
2 Review of PEM Fuel Cell Degradation Phenomena and Mechanisms 20
3 Membrane Degradation 24
3.1. Stress in Membrane and MEAs 25
3.2. Mechanical Characterization of Membranes 29
3.3. Chemical Degradation Processes 33
3.4. Mechanical Degradation Processes 36
3.5. Interactions of Chemical and Mechanical Degradation 44
4 Accelerated Testing and Life Prediction 49
4.1. Accelerated Degradation Testing and Degradation Metrics 49
4.2. Progressive Degradation Model of Combined Effects 53
5 Mitigation 57
Acknowledgments 60
References 60
2 Modeling of Membrane-Electrode-Assembly Degradation in Proton-Exchange-Membrane Fuel Cells -- Local H2 Starvation and Start--Stop Induced Carbon-Support Corrosion 63
1 Introduction 63
2 Kinetic Model 67
2.1. Electrode Kinetics 67
2.2. Local H2 Starvation Model 72
2.3. Start--Stop Model 75
3 Coupled Kinetic and Transport Model 78
3.1. Model Description 78
3.2. Local H2 Starvation Simulation 81
3.3. Start--Stop Simulation 90
4 Pseudo-Capacitance Model 94
4.1. Mechanism Description 94
4.2. Model Description 96
4.3. The Pseudo-capacitive Effect 98
5 Summary and Outlook 99
Acknowledgments 101
List of Symbols 101
References 103
3 Cold Start of Polymer Electrolyte Fuel Cells 107
1 Introduction 107
2 Equilibrium Purge Cold Start 113
2.1. Equilibrium Purge 114
2.2. Isothermal Cold Start 115
2.3. Proton Conductivity at Low Temperature 115
2.4. Effects of Key Parameters 118
2.4.1. Initial Membrane Water Content 118
2.4.2. Startup Current Density 121
2.4.3. Startup Temperature 124
2.5. ORR Kinetics at Low Temperatures 125
2.6. Short-Purge Cold Start 128
3 Water Removal During Gas Purge 129
3.1. Introduction 130
3.2. Purge Curve 132
3.3. Two Characteristic Parameters for Water Removal 133
3.4. Stages of Purge 135
3.5. Effect of Key Parameters 136
3.5.1. Purge Cell Temperature 136
3.5.2. Purge Gas Flow Rate 139
3.5.3. Matching Two Parameters 141
3.6. HFR Relaxation 142
4 Concluding Remarks 144
References 145
4 Species, Temperature, and Current Distribution Mapping in Polymer Electrolyte Membrane Fuel Cells 147
1 Introduction 147
2 Species Distribution Mapping 148
2.1. Species and Properties of Interest 148
2.1.1. Hydrogen 148
2.1.2. Oxygen 148
2.1.3. Water 148
2.1.4. Contaminants and Diluents 149
2.1.5. Pressure Drop 149
2.1.6. Flow Distribution 150
2.2. Methodology and Results 150
2.2.1. Pressure Drop Measurement 150
2.2.2. Gas Composition Analysis 151
2.2.3. Neutron Imaging 153
2.2.4. Magnetic Resonance Imaging 156
2.2.5. X-ray Imaging 158
2.2.6. Optically Transparent Fuel Cells 159
2.2.7. Embedded Sensors 165
2.2.8. Other Methods 166
2.3. Design Implications 167
3 Temperature Distribution Mapping 170
3.1. Methodology and Results 171
3.1.1. IR Transparent Fuel Cells 171
3.1.2. Embedded Sensors 172
3.2. Design Implications 173
4 Current Distribution Mapping 174
4.1. Methodology and Results 174
4.1.1. Partial MEA 174
4.1.2. Segmented Cells 175
4.1.3. Other Methods 181
4.2. Design Implications 183
5 Concluding Remarks 184
References 185
5 High-Resolution Neutron Radiography Analysis of Proton Exchange Membrane Fuel Cells 193
1 Introduction 193
2 Neutron Radiography Facility Layout And Detectors 195
2.1. Neutron Sources and Radiography Beamlines 195
2.2. Neutron Imaging Detectors 199
3 Water Metrology with Neutron Radiography 202
3.1. Neutron Attenuation Coefficient of Water, µw 202
3.2. Sources of Uncertainties in Neutron Radiography 205
3.2.1. Counting Statistics 206
3.2.2. Beam Hardening 208
3.2.3. Background Subtraction 208
3.2.4. Changes in the Total Neutron Scattering from Water Absorbed in the Membrane 209
3.2.5. Image Spatial Resolution 210
4 Recent In Situ High-Resolution Neutron Radiography Experiments of PEMFCs 213
4.1. Proof-of-Principle Experiments 213
4.2. In Situ, Steady-State Through-Plane Water Content 214
4.3. Dynamic Through-Plane Mass Transport Measurements 215
5 Conclusions 216
Acknowledgments 217
References 217
6 Magnetic Resonance Imaging and Tunable Diode Laser Absorption Spectroscopy for In-Situ Water Diagnostics in Polymer Electrolyte Membrane Fuel Cells 219
1 Introduction 219
2 Magnetic Resonance Imaging (MRI): As a Diagnostic Tool for In-Situ Visualization of Water Content Distribution in PEMFC s 220
2.1. Basic Principle of MRI 220
2.2. MRI System Hardware for PEMFC Visualization 224
2.3. MRI Signal Calibration for Water Content in PEM 227
2.4. In Situ Visualization of Water in PEMFC Using MRI 227
3 Tunable Diode Laser Absorption Spectroscopy (TDLAS): As a Diagnostic Tool for In-Situ Detection of Water Vapor Concentration in PEMFC s 231
3.1. Basic Principle of TDLAS 231
3.2. TDLAS System Hardware for Water Vapor Measurement 232
3.3. TDLAS Signal Calibration for Measurement of Water Vapor Concentration 234
3.4. In Situ Measurement of Water Vapor in PEMFC Using TDLAS 237
4 Summary 240
References 240
7 Characterization of the Capillary Properties of Gas Diffusion Media 243
1 Introduction 243
1.1. Motivation 244
2 Basic Considerations 247
3 Measurement of Capillary Pressure Curves 251
4 Interpretation of Capillary Pressure Curves 259
4.1. Capillary Pressure Hysteresis 259
4.2. Effect of Hydrophobic Coating 262
4.3. Effect of Compression 264
4.4. Water Breakthrough Condition 266
4.5. Finite-Size Effects 267
4.6. Effect of Microporous Layer 267
5 Conclusion and Outlook 268
References 270
8 Mesoscopic Modeling of Two-Phase Transport in Polymer Electrolyte Fuel Cells 273
1 Introduction 273
2 Model Description 276
2.1. Stochastic Microstructure Reconstruction Model 276
2.1.1. Catalyst Layer Structure Generation 277
2.1.2. Gas Diffusion Layer Structure Generation 279
2.2. Lattice Boltzmann Model 282
2.2.1. Two-phase LB Model Description 283
3 Two-Phase Simulation 289
3.1. Two-phase Transport Mechanism 289
3.2. Two-phase Numerical Experiments and Setup 291
4 Two-Phase Behavior and Flooding Dynamics 295
4.1. Structure-Wettability Influence 295
4.2. Effect of GDL Compression 302
4.3. Evaluation of Two-Phase Relations 306
4.4. Effect of Liquid Water on Performance 311
5 Summary and Outlook 320
Acknowledgments 322
References 322
9 Atomistic Modeling in Study of Polymer Electrolyte Fuel Cells -- A Review 325
1 Introduction 325
2 Fundamentals of Atomistic Modeling 330
2.1. Ab Initio Modeling of Materials 330
2.1.1. Adiabatic Approximation 330
2.1.2. Hatree--Fock Approximation and Single Electron Hamiltonian 331
2.1.3. Density Function Theory 332
2.1.4. Ab Initio Quantum Chemistry Computation 333
2.1.5. Ab Initio Molecular Dynamics 334
2.2. Classical Molecular Dynamic Modeling 335
2.3. Monte Carlo Modeling 338
2.3.1. The Metropolis Algorithm 338
2.3.2. Kinetic Monte Carlo Modeling 338
2.4. Advancement of MD Methods 339
2.4.1. Empirical Valence Bond Models 339
2.4.2. MD Modeling with Reactive Force Field 341
2.4.3. Methods for Accelerating Molecular Dynamics Simulations 342
3 Modeling of Oxygen Electroreduction Reaction Catalysts 343
3.1. The Interface Structure 344
3.1.1. Ab Initio Modeling of Interface Structure in Aqueous Solutions 346
3.1.2. MD Modeling of Interface Structure on Catalysts in Aqueous Solution 350
3.1.3. MD Modeling of Interface Structure of Polymer Electrolyte/Catalysts Interface 352
3.2. Chemsorption on Catalysts 357
3.2.1. Bond Strength of Adsorbed Oxygen Atom 358
3.2.2. Adsorption Process on Transition Metals 358
3.2.3. On Bimetallic Alloys 359
3.3. Oxygen Electroreduction Reaction with an Emphasis on Charge Transfer at Metal/Water Interface 361
4 Modeling of Oxidation of Carbon Monoxide and Methanol 372
4.1. ''Vapor Phase'' Model 372
4.2. Realistic ''Liquid Phase'' Model 375
5 Modeling of Transport Processes in Nafion Polymer Electrolytes 378
5.1. Theoretical Views of Proton Transport in Aqueous Systems and in Hydrated Nafion Membranes 378
5.1.1. In Aqueous Solution 378
5.1.2. In Hydrated Membrane (Nafion) 380
5.2. Ab Initio Models 381
5.3. Classic MD Models 385
5.4. Empirical Valence Bond and ReaXFF Models 389
6 Summarizing Remarks 391
Acknowledgment 394
Reference 394
Index 399