Introduction to Fuel Cells San Ping Jiang · Qingfeng Li

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Introduction to Fuel Cells Electrochemistry and Materials SanPingJiang Qingfeng Li WA School of Mines: Minerals, Energy Department of Energy Conversion and Chemical Engineering and Storage Curtin University Technical University of Denmark Perth, WA, Australia Lyngby, Denmark

ISBN 978-981-10-7625-1 ISBN 978-981-10-7626-8 (eBook) https://doi.org/10.1007/978-981-10-7626-8

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This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Preface

Fuel cells were initially developed for the space mission programs in 1960s and have today well demonstrated for automobiles, portable electronics, and large-scale power generation plants. The development has appreciably endorsed by the ever-growing concern of fossil fuel depleting and global warming, and in the last years by the potential synergies with renewable energies and the future hydrogen economy. There are quite a number of fuel cell books available in the market. A majority of the books are technically orientated, aimed at updating the detailed progress from material science, kinetic mechanisms, characterization methodologies to technological integration of membrane-electrode assemblies, stacks, fuel processors, and system demonstration. These types of books are interdisciplinary including thematic monographs, symposium proceedings, and a variety of comprehensive handbooks. They are written by fuel cell experts and scientists and suitable for the reader of researchers, professional engineers, and other fuel cell workers in the field. As the interest in fuel cells diffuses well beyond the scientific and technical community, the fuel cell topics is of daily discussion in news media and popular teaching courses in university campuses. The fundamental principles of fuel cells are covered by several well-written textbooks. This type of books is introducing thermodynamics, basic electrochemistry, functional materials, components, performance, and applications. They are suitable for the reader of varied engineering back- grounds to learn what fuel cells are, how fuel cells work, and why they offer the high efficiency, zero emission, and potential sustainability. There is a need for fuel cell textbooks to fill up the gap in between. One, for example, outlines the field at a fundamental thermodynamics, electrochemistry, and material level that can be understood by those who are new in the field with a general engineering background, while the content is advanced enough to provide essential knowledge of technical and material insights for those who are doing or wish to do research in the field. This is what the authors of the present book have attempted to do. Both authors of the book have been doing research and teaching fuel cell courses for more than thirty years. A difficulty encountered in teaching is the lack of examples and problems in fuel cells, which are essential to bridge between the basic knowledge

v vi Preface and skill to handle practical problems for students and engineers. It is therefore attempted to include illustrative and practical examples and problems through the chapters of this book. From numerous examples and referecenes, readers can also ﬁnd detailed information in the experimental design and techniques commonly used in the studies of fuel cells. The book is organized in four parts. Part I of the book is a brief introduction of fundamentals, though in a practical way, of fuel cells including thermodynamics, electrochemistry, and fueling scenarios. The other three parts of the book are devoted to fuel cell technologies. Of types of the technologies, emphasis is placed on polymer electrolyte membrane fuel cells (Part II) and solid oxide fuel cells (Part III), each covering principle and materials, reaction, characterization, microstructure, and fabrication. Many examples of procedures and protocols are from our own lab prac- tice while well selected information from literature is also provided. The last part of the book presents the rest types of fuel cells, i.e., alkaline fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, and the emerging type of protonic ceramic fuel cells, microbial fuel cells, and biofuel cells. The book would not be ﬁnished without help and contributions from past and present colleagues, students, research fellows, and collaborators of both authors who would like to take this opportunity to thank: • Prof. Chen Kongfa and Dr. Ai Na of Fuzhou University; Dr. Zhang Lan of Nanyang Technological University; Prof. Cheng Yi of Central South University; Prof. Zhao Ling of China University of Geosciences; Prof. He Tianmin of Jilin University; Dr. Zhang Jin and Prof. Lu Shanfu of Beihang University; Dr. He Shuai of University of St. Andrew; and Dr. Liu Yu, Dr. Zhao Shiyong, Dr. Zhang Xiao, Ms. Sun Yi and Ms. Zhang Xiaoran of Curtin University for providing raw materials and numerous drawings • Prof. Li Jian and Prof. Pu Jian of Huazhong University of Science and Technology; Prof. Shao Zongping of Curtin University; and Prof. John Zhu of Queensland University for valuable comments and suggestions on the SOFC chapters • Prof. Gordon Parkinson of Curtin University for painstakingly reading and editing of the book chapters • Prof. Jens Oluf Jensen for sharing a lecturing course (hydrogen energy and fuel cells) in last 18 year at DTU from which one of the authors has received many inspiration in writing this book • Dr. Lars N. Cleemann, Dr. Erik Christensen, and Dr. David Aili for sharing an experimental course (hydrogen and fuel cell chemistry) at DTU for the last 15 years. The teaching materials have been the basis for some of the chapter content • Dr. David Aili and Dr. Yang Hu for reading and commenting book chapters and providing graphs. These acknowledgements would not be complete without thanking our family members. SPJ would like to take this opportunity to thank his wife, Choo, his life companion for 30 years, for taking care of all other aspects of his life while he was involved in writing this book. Prof. Jiang would also like to thank his three beautiful children, Yin, Weiping, and Danhua, for the understanding, patience, and Preface vii support. QL would like to thank his family, wife Tianqing and son Mike, for their understanding and constant supportive presence through the time spent on writing this book. Without their encouragement and support, this book would not be possible. Last but not least, the publication of the book would not be possible without the encouragement and help from the editorial staff at Springer and special thanks go to June Tong for the initiation of the project, Umamagesh A P, Sridevi Purushothaman, Sunny Guo, and Nobuko Hirota for the constant support and conductive environment for pursuing this type of project.

Perth, Australia San Ping Jiang Lyngby, Denmark Qingfeng Li Contents

Part I Fundamentals 1 Introduction ...... 3 1.1 Fuel Cells in the Hydrogen Chain ...... 3 1.2 A Brief History of Fuel Cells ...... 5 1.3 Types, Construction, and Components of Fuel Cells ...... 8 1.3.1 Fuel Cell Classiﬁcation ...... 8 1.3.2 Construction and Components of Fuel Cells ...... 9 1.3.3 Brief Summary of Each Type of Fuel Cells ...... 12 1.4 Fuel Cells Versus Batteries ...... 16 1.5 Unitized Regenerative Fuel Cells and Reversible Fuel Cells . . . . 17 1.6 Applications and Prospect of Fuel Cell Technologies ...... 19 1.7 Summary ...... 23 1.8 Questions ...... 24 1.9 General Readings ...... 25 References ...... 25 2 Fuel Cell Thermodynamics ...... 27 2.1 Internal Energy, Heat, Work, and Entropy ...... 27 2.2 EnthalpyandGibbsFreeEnergy ...... 31 2.2.1 Deﬁnition of Enthalpy and Gibbs Free Energy ...... 31 2.2.2 Gibbs Free Energy from First and Second Thermodynamics Laws ...... 32 2.2.3 EnthalpyofFormation...... 33 2.2.4 Effect of Temperature on the Change in Enthalpy andEntropy...... 36 2.2.5 Effect of Temperature on Gibbs Free Energy ...... 40 2.2.6 Gibbs Free Energy and Electrical Work ...... 41 2.2.7 Thermodynamic Reversible Potential and Thermoneutral Potential ...... 43

ix x Contents

2.2.8 Effect of Temperature and Pressure on Reversible Potential ...... 46 2.3 NernstEquation...... 48 2.4 Comparison of Work Done by a Heat Engine and Fuel Cell . . . . . 51 2.4.1 Work Done in a Heat Engine and Carnot Efficiency ...... 52 2.4.2 Fuel Cell Efficiency, Stoichiometry Number, Fuel and Oxygen Utilization Efficiency ...... 54 2.4.3 Other Attributes of ICE and Fuel Cells ...... 60 2.5 Thermodynamics and Efficiency of Water Electrolysis ...... 60 2.5.1 Basic Thermodynamics of Water Electrolysis ...... 61 2.5.2 Thermal Balance of Electrolysis Cells ...... 62 2.5.3 Energy Efficiency of Water Electrolysis ...... 63 2.5.4 High-TemperatureElectrolysis ...... 64 2.6 Summary ...... 65 2.7 Questions ...... 66 2.8 General Readings ...... 68 3 Fuel Cell Electrochemistry ...... 69 3.1 Electrochemistry at the Interface ...... 69 3.1.1 Origin of Double Layer Structure ...... 70 3.1.2 Standard Hydrogen Reference Electrodes ...... 72 3.1.3 Other Reference Electrodes ...... 75 3.1.4 Electrode Potential and Standard Reduction Potential ...... 77 3.1.5 Concentration Cells ...... 79 3.2 Activation and Activation Polarization Loss ...... 81 3.2.1 Why Charge Transfer at the Interface ...... 81 3.2.2 Butler–VolmerEquation ...... 83 3.2.3 TafelPlot...... 86 3.2.4 Effect of Exchange Current Density ...... 88 3.2.5 EffectofTafelSlope ...... 91 3.3 OhmicPolarizationLoss ...... 92 3.4 Mass Transport and Concentration Polarization in Steady State ...... 95 3.5 I-VCharacteristics ...... 99 3.5.1 Cell Voltage and Various Types of Voltage Losses . . . . 99 3.5.2 Open-Circuit Voltage Loss ...... 101 3.5.3 I-V Characteristics and Materials Issues ...... 104 3.6 Basic Electrochemical Techniques ...... 106 3.6.1 Rotating Disk and Rotating Ring Disk Electrodes . . . . 106 3.6.2 Linear Sweeping and Cyclic Voltammetry Techniques ...... 112 3.6.3 Electrochemical Impedance Spectroscopy (EIS) ...... 114 3.7 Summary ...... 119 Contents xi

3.8 Questions ...... 121 3.9 General Readings ...... 122 References ...... 122 4 Fuels for Fuel Cells ...... 123 4.1 Introduction ...... 123 4.2 Hydrogen Production ...... 126 4.2.1 SteamReforming ...... 128 4.2.2 WaterElectrolysis ...... 130 4.3 Hydrogen Storage ...... 141 4.3.1 Physical Storage of Hydrogen ...... 141 4.3.2 Reversible and Irreversible Hydrides ...... 142 4.4 Methanol, Ethanol, Formic Acid, and Other Liquid Fuels ...... 144 4.4.1 Electrochemical Oxidation of Alcohols ...... 145 4.4.2 Effect of pH and Temperature on Alcohol OxidationReactions ...... 153 4.4.3 Energy Density, Environment Effect, and By-Products of Various Fuels ...... 157 4.5 Ammonia,Urea,andHydrazine ...... 159 4.5.1 AmmoniaOxidationReaction ...... 159 4.5.2 Hydrazine Oxidation Reaction ...... 162 4.5.3 ToxicityIssues ...... 164 4.6 Natural Gas, Hydrocarbons, and Biomass-Derived Synthetic Fuels ...... 164 4.7 Summary ...... 166 4.8 Questions ...... 167 References ...... 168

Part II Polymer Electrolyte Membrane Fuel Cells 5 Polymer Electrolyte Membrane Fuel Cells: Principles and Materials ...... 173 5.1 Introduction ...... 173 5.2 Proton-Conducting Electrolytes ...... 174 5.2.1 Electrolytes for Low-Temperature Fuel Cells ...... 174 5.2.2 Proton Conduction Mechanisms and Materials ...... 177 5.3 Proton Exchange Membranes ...... 181 5.3.1 Poly(Perﬂuorosulfonic Acid) Membranes ...... 182 5.3.2 Short Side-Chain PFSA Membranes ...... 190 5.3.3 PFSA Composite Membranes ...... 191 5.3.4 Alternative Membranes ...... 195 5.4 Electrocatalysts ...... 196 5.4.1 Anode Catalysts ...... 197 5.4.2 Cathode Catalysts ...... 198 5.4.3 Carbon Supports ...... 207 5.5 Electrodes and Membrane Electrode Assembly ...... 214 xii Contents

5.5.1 Gas Diffusion Layer ...... 214 5.5.2 Microporous Layers ...... 218 5.5.3 Catalyst Layer ...... 219 5.6 Bipolar Plates and Seals ...... 222 5.7 Summary ...... 223 5.8 Questions ...... 224 5.9 General Readings ...... 226 References ...... 227 6 Polymer Electrolyte Membrane Fuel Cells: Fabrication and Characterization ...... 229 6.1 Proton Exchange Membranes ...... 229 6.1.1 PFSA Membrane Fabrication ...... 229 6.1.2 Ion-Exchange Capacity and Equivalent Weight ...... 231 6.1.3 Water Uptake and Swelling ...... 232 6.1.4 Proton Conductivity ...... 235 6.1.5 ElectroosmoticDragofWater ...... 238 6.1.6 Water and Methanol Diffusion ...... 241 6.1.7 Solubility and Diffusion of Oxygen ...... 242 6.1.8 Permeability of Hydrogen ...... 244 6.1.9 Methanol Crossover—Liquid and Vapor ...... 248 6.1.10 Fenton Test ...... 252 6.1.11 Mechanical Properties ...... 254 6.1.12 Thermal Stability Test ...... 256 6.2 Catalyst Synthesis ...... 257 6.2.1 Impregnation–Reduction Method ...... 257 6.2.2 ColloidalAdsorptionMethod...... 259 6.2.3 Self-assembly Method on CNT and Graphene Supports ...... 261 6.3 ExSituCharacterizationofCatalysts...... 262 6.3.1 Catalyst Ink and Thin Catalyst Film ...... 263 6.3.2 Three-Electrode Cell Conﬁguration ...... 263 6.3.3 Preconditioning and ORR Activity Measurement . . . . . 265 6.3.4 DeterminationoftheECSA ...... 266 6.3.5 Analysis of the Polarization Curves ...... 268 6.3.6 Stability Test ...... 271 6.3.7 Half-CellCharacterization ...... 272 6.4 Fuel Cell Test for in Situ Characterization ...... 275 6.4.1 Cell Assembling and Pretest Conditioning ...... 275 6.4.2 DeterminationofECSA ...... 276 6.4.3 Membrane Durability Test ...... 277 6.4.4 Catalyst Stability Test ...... 279 6.5 Summary ...... 285 6.6 Questions ...... 286 6.7 General Readings ...... 287 References ...... 288 Contents xiii

7 Polymer Electrolyte Membrane Fuel Cells: Performance and Operation ...... 291 7.1 Performance and Analysis ...... 291 7.1.1 Analysisofi-VCurves ...... 293 7.1.2 OhmicLosses ...... 294 7.1.3 ORRKineticParameters...... 295 7.1.4 MassTransportLosses ...... 298 7.2 FuelingOptionsandCOPoisoning ...... 299 7.2.1 COAdsorptiononPt ...... 300 7.2.2 COPoisoningEffect ...... 301 7.2.3 Relative Activity and Temperature Effect ...... 302 7.2.4 CO Poisoning Mitigation and Bifunctional Mechanism ...... 302 7.2.5 Catalysts for Methanol Electro-Oxidation ...... 304 7.2.6 OtherEffectsofCO...... 304 7.3 Water Management ...... 305 7.3.1 Water Balance and Transport ...... 305 7.3.2 Saturated Water Vapor Pressure and Relative Humidity ...... 306 7.3.3 Self-Humidification ...... 307 7.3.4 ExternalHumidification ...... 309 7.3.5 Modified and Thinner Membranes ...... 310 7.4 Thermal Management ...... 311 7.4.1 Heat Generation ...... 311 7.4.2 Cooling Duty and Radiator Area ...... 312 7.4.3 AirCoolingVersusWaterCooling ...... 313 7.4.4 Operating Points and Stack Calculation ...... 314 7.5 Durability Issues and Mitigation ...... 314 7.5.1 Status and Target of Durability ...... 314 7.6 Summary ...... 321 7.7 Questions ...... 322 References ...... 323 8 High-Temperature Polymer Electrolyte Membrane Fuel Cells ..... 325 8.1 WhyandHowHighTemperatures ...... 325 8.2 Polybenzimidazoles and Their Interactions with Phosphoric Acids...... 326 8.2.1 Synthesis and Molecule Weight Determination ...... 326 8.2.2 Membrane Casting from DMAc Solutions andAcidDoping ...... 328 8.2.3 Direct Cast Membranes ...... 329 8.2.4 Membrane Characterization ...... 330 8.2.5 PBIVariants ...... 332 8.2.6 Cross-linking, Blends, and Thermal Curing ...... 332 8.2.7 PBI Composite Membranes ...... 336 xiv Contents

8.3 Catalysts and Electrodes ...... 336 8.3.1 Catalysts ...... 336 8.3.2 Gas Diffusion Electrodes ...... 341 8.3.3 Membrane Electrode Assemblies ...... 341 8.4 Fuel Cell Performance and Operation ...... 344 8.4.1 Performance and Pt Loading ...... 344 8.4.2 Impact of Fuel Impurities and Water ...... 345 8.5 Alternative High-Temperature Membranes ...... 346 8.5.1 Non-PBI Based High-Temperature Membranes ...... 346 8.5.2 Inorganic High-Temperature Membranes ...... 347 8.6 Durability and Commercialization ...... 349 8.7 Summary ...... 351 8.8 Questions ...... 351 8.9 General Readings ...... 352 References ...... 352

Part III Solid Oxide Fuel Cells 9 Solid Oxide Fuel Cells: Principles and Materials ...... 357 9.1 Introduction ...... 357 9.1.1 OperationPrinciples ...... 357 9.1.2 Charge Transport in Oxide Materials ...... 360 9.2 Electrolyte ...... 369 9.2.1 Zirconium Oxides ...... 372 9.2.2 CeriumOxides ...... 375 9.2.3 Lanthanum Strontium Magnesium Gallate Perovskites ...... 377 9.2.4 Apatite Oxides ...... 379 9.2.5 BismuthOxides ...... 380 9.3 Anode ...... 381 9.3.1 Ni-Based Cermet Anode ...... 383 9.3.2 Cu/CeO2/YSZ-Based Anode ...... 387 9.3.3 Ceramic Oxide Anode ...... 387 9.4 Cathode ...... 389 9.4.1 Lanthanum Strontium Manganite ...... 390 9.4.2 Lanthanum Strontium Cobalt Ferrite ...... 395 9.4.3 Other Perovskites, Double Perovskites, and Ruddlesden-Popper Structured Oxides ...... 396 9.4.4 Composite Cathode ...... 400 9.5 Interconnect and Sealant ...... 403 9.5.1 Interconnect ...... 403 9.5.2 Sealants ...... 410 9.6 CellStructuresandStackDesign ...... 412 9.6.1 CellStructures ...... 412 9.6.2 StackDesign...... 413 Contents xv

9.7 VariationsofSOFCs ...... 414 9.7.1 Single-Chamber Solid Oxide Fuel Cells ...... 415 9.7.2 Metal-Supported Solid Oxide Fuel Cells ...... 416 9.7.3 Direct Carbon Fuel Cells ...... 417 9.8 Summary ...... 418 9.9 Questions ...... 420 References ...... 422 10 Solid Oxide Fuel Cells: Reactions ...... 425 10.1 Surface Segregation of Oxide Electrodes ...... 425 10.1.1 Surface Segregation Under Open Circuit ...... 426 10.1.2 Surface Segregation Under Polarization ...... 428 10.1.3 ANote ...... 435 10.2 Reactions at the Cathode ...... 436 10.2.1 Activation Process ...... 436 10.2.2 Oxygen Reduction Reaction ...... 439 10.2.3 Effect of Oxygen Vacancies ...... 444 10.3 Reactions at the Anode ...... 446 10.3.1 Hydrogen Oxidation Reaction ...... 446 10.3.2 Hydrocarbon Fuel Oxidation Reaction ...... 454 10.3.3 Redox Reaction ...... 457 10.4 InterfaceandInterfaceReactions ...... 458 10.4.1 LSM and YSZ (Doped Ceria) Systems ...... 458 10.4.2 Interface and Interaction Between LSCF and YSZ . . . . 462 10.4.3 LSCF/GDC/YSZInterface ...... 466 10.4.4 Other Interfaces ...... 466 10.5 Reaction with Contaminants ...... 467 10.5.1 Reactions Between Cathode and Contaminants ...... 468 10.5.2 Reaction Between Anode and Contaminants ...... 478 10.5.3 Contaminant-Tolerant Electrodes ...... 483 10.6 Summary ...... 487 10.7 Questions ...... 490 References ...... 492 11 Solid Oxide Fuel Cells: Techniques and Characterization ...... 497 11.1 Electrode Arrangement and Test Stations ...... 497 11.1.1 Test Station Design and Arrangement ...... 497 11.1.2 Electrode Arrangements ...... 501 11.1.3 Comparative Experimental Approach ...... 504 11.2 Cell Conﬁgurations and Performance Scalability ...... 505 11.2.1 Cell Conﬁgurations ...... 505 11.2.2 SymmetricCell...... 506 11.2.3 Polarization Performance Analysis ...... 509 11.3 Equipotential Line and Constriction Effect ...... 517 11.3.1 EquipotentialLine ...... 517 xvi Contents

11.3.2 Special Voltage Probe and Resistance Distribution...... 518 11.3.3 Relationship Between Validity of Reference Electrode and Electrolyte Thickness ...... 525 11.3.4 ConstrictionEffect...... 527 11.4 Equivalent Circuit Analysis in Electrochemical Impedance Spectroscopy ...... 529 11.4.1 Equivalent Circuit for Capacitance Impedance ...... 531 11.4.2 Equivalent Circuit for Inductance Impedance ...... 533 11.4.3 Physical Signiﬁcance of Equivalent Circuit Elements ...... 535 11.4.4 Impedance Measurement in SOFCs ...... 537 11.5 Galvanostatic Current Interruption Technique ...... 539 11.5.1 Comparison of EIS and GCI Techniques ...... 541 11.6 Conductivity Measurement of SOFC Components andMaterials ...... 543 11.6.1 Two-Probe and Four-Probe Methods ...... 543 11.6.2 Conductivity Measurement of Porous Electrode Coating ...... 545 11.6.3 Contact Resistance Between Electrode andCurrentCollector ...... 547 11.6.4 Ionic Conductivity of Electrolyte by EIS ...... 548 11.7 Other Properties ...... 550 11.7.1 Oxygen Surface Diffusion and Exchange CoefﬁcientMeasurements ...... 550 11.7.2 Porosity and Density Measurement ...... 552 11.7.3 Focus Ion Beam and Scanning Transmission ElectronMicroscopy(FIB-STEM) ...... 553 11.8 Summary ...... 557 11.9 Questions ...... 558 References ...... 559 12 Solid Oxide Fuel Cells: Fabrication and Microstructure ...... 561 12.1 Introduction ...... 561 12.2 Powder Synthesis Methods ...... 562 12.2.1 Solid-State Reaction and Physical Mixing Methods ...... 562 12.2.2 SolutionCombustionMethod...... 563 12.2.3 Co-precipitationMethod...... 566 12.2.4 Pechini and Polymeric Complexing Method ...... 568 12.2.5 Sol–GelMethod ...... 570 12.2.6 Gel-CastingMethod ...... 571 12.3 Fabrication Techniques for Electrolyte and Electrode Coatings ...... 574 12.3.1 DiePressingMethod ...... 575 Contents xvii

12.3.2 Tape-Casting Method ...... 576 12.3.3 Screen-Printing Method ...... 579 12.3.4 Chemical Vapor Deposition and Atomic Layer Deposition ...... 580 12.3.5 Electrochemical Vapor Deposition ...... 580 12.3.6 Magnetron Sputtering Techniques ...... 581 12.3.7 Pulsed Laser Deposition ...... 584 12.3.8 Plasma Spray Deposition ...... 584 12.3.9 Slurry-Coating, Spin-Coating and Dip-Coating Methods ...... 586 12.3.10 Electrophoretic Deposition ...... 589 12.3.11 Spray Pyrolysis and Flame-Assisted Vapor Deposition ...... 591 12.4 High-Temperature Sintering Process ...... 592 12.4.1 Anode ...... 593 12.4.2 Cathode ...... 595 12.4.3 SinteringProﬁle ...... 597 12.4.4 High-Temperature Sintering Aids and Solid-State Reactive Sintering ...... 599 12.5 Direct Assembly and Polarization-Induced Interface ...... 600 12.6 Nano-Structured Electrodes ...... 603 12.6.1 Wet-Inﬁltration Techniques ...... 603 12.6.2 Decoration and Polarization-Induced Phase Migration...... 608 12.6.3 Nanosized Catalysts by in Situ Exsolution ...... 611 12.6.4 Microstructure and Microstructure Stability ...... 612 12.7 CellFabrication ...... 614 12.7.1 Planar Cells ...... 614 12.7.2 TubularCells ...... 615 12.8 Summary ...... 616 12.9 Questions ...... 618 References ...... 619

Part IV Other Fuel Cells 13 Alkaline Fuel Cells ...... 623 13.1 Introduction ...... 623 13.2 Alkaline Fuel Cells ...... 624 13.2.1 ElectrolyteforAFC ...... 624 13.2.2 Catalysts ...... 625 13.2.3 Gas Diffusion Electrodes for Liquid Electrolytes . . . . . 627 13.2.4 Electrolyte Conﬁguration ...... 632 13.2.5 StackDesign...... 636 13.2.6 Carbonization and CO2 Scrubbing ...... 636 13.2.7 Performance and Durability ...... 638 xviii Contents

13.3 Anion Exchange Membrane Fuel Cells ...... 639 13.3.1 AEMElectrolyte ...... 640 13.3.2 CatalystDevelopment ...... 643 13.3.3 Performance ...... 644 13.4 Summary ...... 646 13.5 Questions ...... 647 References ...... 648 14 Phosphoric Acid Fuel Cells ...... 649 14.1 Introduction ...... 649 14.2 Phosphoric Acid ...... 649 14.2.1 AcidChemistry ...... 649 14.2.2 Conductivity and Mechanism ...... 651 14.2.3 Vapor Pressure and Thermal Stability ...... 653 14.3 Cell Components ...... 654 14.3.1 Catalysts ...... 654 14.3.2 Gas Diffusion Electrodes ...... 660 14.3.3 MatrixandAcidReservoir ...... 661 14.3.4 Bipolar or Separate Plates ...... 663 14.3.5 Seals and Coolers ...... 663 14.4 Performance and Cell Management ...... 664 14.4.1 Performance and Lifetime ...... 664 14.4.2 Acid Evaporation and Mitigation ...... 667 14.4.3 Migration of Acid and Management ...... 667 14.5 Summary ...... 668 14.6 Questions ...... 669 References ...... 670 15 Molten Carbonate Fuel Cells ...... 673 15.1 Introduction ...... 673 15.2 Electrolytes ...... 676 15.2.1 Alkali Metal Carbonates ...... 676 15.2.2 Acid—BaseChemistry ...... 677 15.2.3 Properties of Molten Carbonate Systems ...... 678 15.2.4 Comparison of Li/K and Li/Na Systems ...... 679 15.3 Cathode Reactions and Materials ...... 680 15.3.1 Oxygen Reduction Reaction in Molten Carbonates ...... 680 15.3.2 Cathode Materials ...... 681 15.3.3 NiODissolutionandPrecipitation...... 681 15.3.4 Electrolyte Additives and Alternative Materials ...... 682 15.4 Anode Reactions and Materials ...... 683 15.5 Matrix and Immobilization of Molten Carbonate Electrolyte . . . . 685 15.5.1 MatrixMaterials...... 685 15.5.2 Immobilization and Distribution of Electrolyte ...... 685 15.5.3 Matrix Stability and Fabrication ...... 686 Contents xix

15.6 ConstructionMaterials ...... 688 15.7 Performance and Durability ...... 689 15.8 Summary ...... 691 15.9 Questions ...... 692 References ...... 692 16 Protonic Ceramic Oxide Fuel Cells, Microbial Fuel Cells, and Biofuel Cells ...... 695 16.1 Protonic Ceramic Oxide Fuel Cells ...... 695 16.1.1 Operation Principle of Protonic Ceramic Oxide Fuel Cells ...... 696 16.1.2 Proton-Conducting Oxides ...... 698 16.1.3 Electrode Materials for PCFCs ...... 701 16.1.4 Other Applications of Proton-Conducting Oxides . . . . . 703 16.1.5 Proton Conductivity Measurement ...... 705 16.2 Microbial Fuel Cells ...... 708 16.2.1 Microbial Fuel Cell Conﬁguration ...... 708 16.2.2 Catalysis in Microbial Fuel Cell Anode ...... 710 16.2.3 Catalysis in Microbial Fuel Cell Cathode ...... 712 16.2.4 Electron Transfer Mechanism ...... 714 16.2.5 Challenges in MFCs ...... 716 16.3 BiofuelCells ...... 716 16.4 Summary ...... 718 16.5 Questions ...... 719 References ...... 719 About the Authors

San Ping Jiang is John Curtin Distinguished Professor at WA School of Mines: Minerals, Energy and Chemical Engineering, Deputy Director of Fuels and Energy Technology Institute, Curtin University and Adjunct Professor of the University of Sunshine Coast, Australia. He obtained his BEng from South China University of Technology, Guangzhou in 1982 and Ph.D. from The City University, London in 1988. He has over 30 years academic and industry R&D experience and has held positions at Essex University in UK, Nanyang Technological University in Singapore, and CSIRO Materials and Manufacturing Division and Ceramic Fuel Cells Ltd in Australia. His research interests encompass fuel cells, water splitting, super- capacitors, solid oxide electrolyzers, CO2 electrolysis, photocatalysis, electrocatalysis, solid-state ionics, and high-temperature solid-state electrochemistry. Professor Jiang has made signiﬁcant contributions to the fundamental knowledge and technological development of electrochemical energy conversion and storage areas and is one of the most cited researchers in fuel cells. Professor Jiang was recognized as a Most Cited Researcher (MCR) in Energy Science and Engineering by Shanghai Jia Tong University’s ARWU/Elsevier in 2016 and a Highly Cited Researcher (HCR)in Cross-Fields by Clarivate Analytics/Web of Science in 2018.

xxi xxii About the Authors

Qingfeng Li is a full professor at Department of Energy Conversion and Storage, Technical University of Denmark. His research areas include proton-conducting electrolytes, electrocatalysts, and the related technologies particularly fuel cells and electrolyzers. He received his Ph.D. in electrochemistry from Northeastern Univer- sity, China, in 1990 and was awarded Doctor Degree of Technices at DTU in 2006. As a research fellow, he started in the middle of 1990s the research on high- temperature polymer electrolyte membrane fuel cells at DTU. He has participated/coordinated more than 20 EU and Nordic research projects within the fuel cell area and leading the 4M Centre devoted to fundamental research on mechanisms, materials, manufacturing, and management of high-temperature polymer electrolyte membrane fuel cells, funded by the Danish Council for Strategic Research and later Innovation Fund Denmark. Professor Li has been involved in teaching a lecturing course (hydrogen energy and fuel cells) since 2004 and an experimental course (hydrogen and fuel cell chemistry) since 2008 at DTU. Abbreviations

AAS Atomic absorption spectroscopy AB-PBI Poly(2,5-benzimidazole) ADL Acid doping level AEC Alkaline electrolysis cell AEM Anion exchange membrane AEMFC Anion exchange membrane fuel cell AFC Alkaline fuel cell AFL Anode function layer ALD Atomic layer deposition AM Acrylamide (C2H3CONH2) AOR Alcohol oxidation reaction APS Ammonium persulfate or atmosphere plasma spray APU Auxiliary power unit ASR Area-speciﬁc resistance AST Accelerated stress test ATR Autothermal reforming BCC Body centered cubic BCV Battery electrical vehicle BFC Biofuel cell BoL Beginning of life BoP Balance of plant BPP Bipolar plate BSCF Barium strontium cobalt ferrite CA Citric acid (C6H8O7) CCCL Cathode current collection layer CCL Cathode contact layer CCM Catalyst-coated membrane CE Counter electrode CFL Cathode functional layer CGH2 Compressed gaseous hydrogen CHP Cogeneration of heat and power CL Catalyst layer xxiii xxiv Abbreviations

CN Coordination number CNT Carbon nanotube CPE Constant-phase element CV Cyclic voltammetry CVD Chemical vapor deposition DAFC Direct alcohol fuel cell DCD Dicyandiamide (C2H4N4) DCFC Direct carbon fuel cell DEFC Direct ethanol fuel cell DFAFC Direct formic acid fuel cell dFAOR Direct formic acid oxidation reaction DFT Density functional theory DHE Dynamic hydrogen electrode DHzFC Direct hydrazine fuel cell DMAc N,N-dimethylacetamide DMF N,N-dimethylformamide DMFC Direct methanol fuel cell DUFC Direct urea fuel cell EC Electrolysis cell ECM Equivalent circuit mode ECR Electrical conductivity relaxation ECSA Electrochemical surface area or electrochemically active surface area EDTA Ethylenediaminetetraacetic acid EG Ethylene glycol EIS Electrochemical impedance spectroscopy EMF Electromotive force EoL End of life EOR Ethanol oxidation reaction EPD Electrophoretic deposition ESB Erbium-stabilized bismuth EVD Electrochemical vapor deposition EW Equivalent weight FA Formic acid FAOR Formic acid oxidation reaction FC Fuel cell FCC Face centered cubic FCV Fuel cell vehicle FER Fluorine ion emission rate GC Glassy carbon GCE Glassy carbon electrode GDC Gadolinium-doped ceria GDE Gas diffusion electrode GDL Gas diffusion layer GNP Glycine–nitrate process Abbreviations xxv

HER Hydrogen evolution reaction HHV High heat value HOR Hydrogen oxidation reaction HP Hemin porcine (C34H32ClFeN4O4) HPA Heteropolyacids HPW or PWA Phosphotungstic acid (H3PW12O40) HR-TEM High-resolution transmission electron microscopy HT-PEMFC High-temperature polymer electrolyte membrane fuel cell HUPD Underpotential hydrogen deposition HzOR Hydrazine oxidation reaction ICE Internal combustion engine ICP-AES Inductive coupled plasma-atomic emission spectrometry IEC Ion exchange capacity IPA Isopropanol or isopropyl alcohol IPAOR Isopropanol or isopropyl alcohol oxidation reaction IT-SOFC Intermediate temperature solid oxide fuel cell K-L equation Koutecky–Levich equation LCCr Lanthanum calcium chromite LH2 Liquid hydrogen LHV Low heat value LSC Lanthanum strontium cobaltite or long side chain in polymer LSCF Lanthanum strontium cobalt ferrite LSCM Lanthanum strontium chromium manganite LSCr Lanthanum strontium chromite LSF Lanthanum strontium ferrite LSGM Lanthanum strontium magnesium gallate LSM Lanthanum strontium manganite LSV Linear scan voltammetry LT-PEMFC Low-temperature polymer electrolyte membrane fuel cell MA Mass activity (of catalysts) MBAM N,N-methylenebis-acrylamide MCFC Molten carbonate fuel cell MD Machine (extrusion) direction MEA Membrane-electrode assembly MET Mediated electron transfer MFC Microbial fuel cell MIEC Mixed ionic and electronic conductivity MOR Methanol oxidation reaction MPL Microporous layer MSAA Mass specific active area MSE Mass specific energy density MS-SOFC Metal-supported solid oxide fuel cell NEXAFS Near-edge X-ray absorption fine structure NG Natural gas NMP N-methyl-2-pyrrolidone xxvi Abbreviations

NMR Nuclear magnetic resonance spectroscopy NP Nano-particle NPMC Non-precious metal catalyst OCP Open-circuit potential OCV Open-circuit voltage OER Oxygen evolution reaction ORR Oxygen reduction reaction P2X Power-to-x(chemicals) PA Phosphoric acid, H3PO4 PA/PBI Phosphoric acid/polybenzimidazole PAFC Phosphoric acid fuel cell PBI Polybenzimidazole PDDA Poly(diallyldimethylammonium chloride) PEEK Poly(ether ether ketone) PEFC Protonic ceramic fuel cell PEI Poly(ethyleneimine) PEM Polymer electrolyte membrane PEMEC Polymer electrolyte membrane electrolysis cell or proton exchange membrane electrolysis cell PEMFC Polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell PES Polyethersulfone PEWE Polymer electrolyte water electrolyzer PFSA Perfluorosulfonic acid PGM Precious group metals PLD Pulsed laser deposition PMG Precious metal group POx Partial oxidation PPA Polyphosphoric acid PPD Peak power density PSS Polysodium-p-styrenesulfonate PSSA Poly(styrenesulfonic acid) PSU Poly(ether sulfone) PTFE Polytetrafluoroethylene PTL Porous transport layer PVDF Poly(vinylidene fluoride) PVP Poly(vinyl pyrrolidone) PWA Phosphotungstic acid QA Quaternary ammonium RDE Rotating disk electrode RDS Rate determining step RE Reference electrode RF Roughness factor RFC Regenerative fuel cell RH Relative humidity (%) Abbreviations xxvii

RHC Relative humidity cycle RHE Reversible hydrogen electrode RP Ruddlesden–Popper structure RRDE Rotating ring disk electrode SA (area) specific activity SAC Single-atom catalysts SCE Saturated calomel electrode SC-SOFC Single-chamber solid oxide fuel cell ScYZ Scandia-stabilized zirconia SDC Samnium-doped ceria SEM Scanning electron microscopy SHE Standard hydrogen electrode SMR Steam methane reforming SOC Solid oxide cell SOEC Solid oxide electrolysis cell SOFC Solid oxide fuel cell SR Steam reforming SSC Short side chain SSR Solid-state reaction STP Standard temperature and pressure TCO Triple conducting oxide TD Transverse direction TEC Thermal expansion coefficient TEM Transmission electron microscopy TEMED N,N,NN-tetra methyl-ethylene diamide TEOS Tetraethoxysilane TFE Tetrafluoroethylene TF-RDE Thin-film rotating disk electrode Tg Glass transition temperature TGA Thermogravimetric analysis THF Tetrahydrofuran TOF Turnover frequency TPB Three-phase boundary URFC Unitized regenerative fuel cell VP Voltage probe VSE Volume-specific energy density WE Working electrode WFR Water formation reaction WGS Water–gas shift reaction XAFS X-ray absorption fine structure XANES X-ray absorption near-edge structure XRD X-ray diffraction YSB Yttria-stabilized bismuth YSZ Yttria-stabilized zirconia Physical Constants and Conversion

Speed of light c 3 × 108 m/s 23 Avogadro’s number NA 6.02 × 10 atoms/mol Boltzmann constant k 1.38 × 10−23 J/K 8.61 × 10−5 eV/K Electron charge q 1.60 × 10−19 C −31 Electron mass me 9.11 × 10 kg −27 Proton mass mp 1.67 × 10 kg Faraday’s constant F 96485.34 C/mol Gas constant R 8.3145 J/mol·K 82.06 atm·cm3/mol·K 83.145 bar·cm3/mol·K 1.987 cal/mol·K 1.987 btu·1b/mol·K 10.740 Pa·ft31b/mol·K Planck’s constant è 6.626 × 10−34 J·s 4.136 × 10−15 eV·s Force 1N= 1 kg/m·s2 1N= 105dyn Distance 1km= 0.622 mile 1m= 3.28 ft Energy 1J= 6.241506 × 1018 eV 1J= 9.478134 × 10−4 Btu 1J= 2.777778 × 10−7 kWh 1 calorie = 4.184 J Pressure 1Pa= 1N/m2 1bar= 100 kPa 1atm= 1.01325 bar (continued) xxix xxx Physical Constants and Conversion

(continued) 1atm= 0.1013 MPa 1atm= 14.6959 psi 1atm= 760 mmHg Power 1W= 1J/s= 1 Nm/s 1W= 1.34 × 10−3 horsepower 1W= 3.415 Btu/h Volume 1m3 = 1000 L 1L= 0.265 gal 1L= 3.53 × 10−2 ft3 Mass 1kg= 2.20 1b