Fuel Cell Systems Explained

ANDREW L. DICKS, PHD is an Independent Consultant and Adjunct Principal Research Fellow at Griffith University, Brisbane, Australia.DAVID A. J. RAND, PHD, SCD was a Chief Research Scientist at CSIRO where, among other duties, he served as scientific advisor on hydrogen and renewable energy. In retirement, he is now a CSIRO Honorary Research Fellow, Melbourne, Australia.

Ever since its initial publication, Fuel Cell Systems Explained has been one of the most approachable books on the subject. Well-written and concise, the third edition maintains that tradition. The scientific and technical sections are clear and logical, and lead the reader carefully through the complexities of fuel cell materials and operating conditions, from basic principles to specific fuel cell types. This is all prefaced by a history of the sector. While this latter may seem tangential to those seeking electrochemical equations, in fact it is both interesting and useful, for example in helping me understand some of the technology development decisions that have been made over the years. It is also interesting to discover that one of the very first applications was of a fuel cell developed by Bacon and trialled in a forklift, perhaps not coincidentally one of the most successful sectors today, and that fuel cells were viewed as superior to batteries as far back as the Gemini space missions; a technology supremacy discussion which is just as live today. - David Hart, Director, E4tech and lead author of the annual Fuel Cell Industry Review The Third Edition of Fuel Cell Systems Explained is an updated version of a book that has always been essential reading for everyone entering into the fuel cell sector, be they student or industrial practitioner. This edition introduces the basic principles of thermodynamics and electrochemical kinetics pertinent to the understanding of fuel cell operation, and determining fuel cell efficiency and voltage losses. But the heart of the book are the six chapters detailing each of the principal fuel cell technologies; proton-exchange membrane fuel cells; alkaline fuel cells; direct liquid fuel cells; phosphoric acid fuel cells; molten carbonate fuel cells and solid oxide fuel cells. There are also useful chapters covering different fuels and fuel processing options, hydrogen storage and a short discussion of balance-of-plant. I am delighted to say that it is a book that I will continue to recommend highly as a first read to all those who join my own research group to work on this exciting technology. - Professor Nigel Brandon OBE FREng, Imperial College London, UK

• Brief Biographies xiiiPreface xvAcknowledgments xviiAcronyms and Initialisms xixSymbols and Units xxv1 Introducing Fuel Cells 11.1 Historical Perspective 11.2 Fuel-Cell Basics 71.3 Electrode Reaction Rates 91.4 Stack Design 111.5 Gas Supply and Cooling 141.6 Principal Technologies 171.7 Mechanically Rechargeable Batteries and Other Fuel Cells 191.7.1 Metal–Air Cells 201.7.2 Redox Flow Cells 201.7.3 Biological Fuel Cells 231.8 Balance-of-Plant Components 231.9 Fuel-Cell Systems: Key Parameters 241.10 Advantages and Applications 25Further Reading 262 Efficiency and Open-Circuit Voltage 272.1 Open-Circuit Voltage: Hydrogen Fuel Cell 272.2 Open-Circuit Voltage: Other Fuel Cells and Batteries 312.3 Efficiency and Its Limits 322.4 Efficiency and Voltage 352.5 Influence of Pressure and Gas Concentration 362.5.1 Nernst Equation 362.5.2 Hydrogen Partial Pressure 382.5.3 Fuel and Oxidant Utilization 392.5.4 System Pressure 392.6 Summary 40Further Reading 413 Operational Fuel-Cell Voltages 433.1 Fundamental Voltage: Current Behaviour 433.2 Terminology 443.3 Fuel-Cell Irreversibilities 463.4 ActivationLosses 463.4.1 The Tafel Equation 463.4.2 The Constants in the Tafel Equation 483.4.3 Reducing the Activation Overpotential 513.5 InternalCurrents and Fuel Crossover 523.6 Ohmic Losses 543.7 Mass-Transport Losses 553.8 Combining the Irreversibilities 573.9 The Electrical Double-Layer 583.10 Techniques for Distinguishing Irreversibilities 603.10.1 Cyclic Voltammetry 603.10.2 AC Impedance Spectroscopy 613.10.3 Current Interruption 65FurtherReading 684 Proton-Exchange Membrane Fuel Cells 694.1 Overview 694.2 Polymer Electrolyte: Principles of Operation 724.2.1 Perfluorinated Sulfonic Acid Membrane 724.2.2 Modified Perfluorinated Sulfonic Acid Membranes 764.2.3 Alternative Sulfonated and Non-Sulfonated Membranes 774.2.4 Acid–Base Complexes and Ionic Liquids 794.2.5 High-Temperature Proton Conductors 804.3 Electrodes and Electrode Structure 814.3.1 Catalyst Layers: Platinum-Based Catalysts 824.3.2 Catalyst Layers: Alternative Catalysts for Oxygen Reduction 854.3.2.1 Macrocyclics 864.3.2.2 Chalcogenides 874.3.2.3 Conductive Polymers 874.3.2.4 Nitrides 874.3.2.5 Functionalized Carbons 874.3.2.6 Heteropolyacids 884.3.3 Catalyst Layer: Negative Electrode 884.3.4 Catalyst Durability 884.3.5 Gas-Diffusion Layer 894.4 Water Management 924.4.1 Hydration and Water Movement 924.4.2 Air Flow and Water Evaporation 944.4.3 Air Humidity 964.4.4 Self-Humidified Cells 984.4.5 External Humidification: Principles 1004.4.6 External Humidification: Methods 1024.5 Cooling and Air Supply 1044.5.1 Cooling with Cathode Air Supply 1044.5.2 Separate Reactant and Cooling Air 1044.5.3 Water Cooling 1054.6 Stack Construction Methods 1074.6.1 Introduction 1074.6.2 Carbon Bipolar Plates 1074.6.3 Metal Bipolar Plates 1094.6.4 Flow-Field Patterns 1104.6.5 Other Topologies 1124.6.6 Mixed Reactant Cells 1144.7 Operating Pressure 1154.7.1 Technical Issues 1154.7.2 Benefits of High Operating Pressures 1174.7.2.1 Current 1174.7.3 Other Factors 1204.8 Fuel Types 1204.8.1 Reformed Hydrocarbons 1204.8.2 Alcohols and Other Liquid Fuels 1214.9 Practical and Commercial Systems 1224.9.1 Small-Scale Systems 1224.9.2 Medium-Scale for Stationary Applications 1234.9.3 Transport System Applications 1254.10 System Design, Stack Lifetime and Related Issues 1294.10.1 Membrane Degradation 1294.10.2 Catalyst Degradation 1294.10.3 System Control 1294.11 Unitized Regenerative Fuel Cells 130Further Reading 1325 Alkaline Fuel Cells 1355.1 Principles of Operation 1355.2 System Designs 1375.2.1 Circulating Electrolyte Solution 1375.2.2 Static Electrolyte Solution 1405.2.3 Dissolved Fuel 1425.2.4 Anion-Exchange Membrane Fuel Cells 1445.3 Electrodes 1475.3.1 Sintered Nickel Powder 1475.3.2 Raney Metals 1475.3.3 Rolled Carbon 1485.3.4 Catalysts 1505.4 Stack Designs 1515.4.1 Monopolar and Bipolar 1515.4.2 Other Stack Designs 1525.5 Operating Pressure and Temperature 1525.6 Opportunities and Challenges 155FurtherReading 1566 Direct Liquid Fuel Cells 1576.1 Direct Methanol Fuel Cells 1576.1.1 Principles of Operation 1606.1.2 Electrode Reactions with a Proton-Exchange Membrane Electrolyte 1606.1.3 Electrode Reactions with an Alkaline Electrolyte 1626.1.4 Anode Catalysts 1626.1.5 Cathode Catalysts 1636.1.6 System Designs 1646.1.7 Fuel Crossover 1656.1.8 Mitigating Fuel Crossover: Standard Techniques 1666.1.9 Mitigating Fuel Crossover: Prospective Techniques 1676.1.10 Methanol Production 1686.1.11 Methanol Safety and Storage 1686.2 Direct Ethanol Fuel Cells 1696.2.1 Principles of Operation 1706.2.2 Ethanol Oxidation, Catalyst and Reaction Mechanism 1706.2.3 Low-Temperature Operation: Performance and Challenges 1726.2.4 High-Temperature Direct Ethanol Fuel Cells 1736.3 Direct Propanol Fuel Cells 1736.4 Direct Ethylene Glycol Fuel Cells 1746.4.1 Principles of Operation 1746.4.2 Ethylene Glycol: Anodic Oxidation 1756.4.3 Cell Performance 1766.5 Formic Acid Fuel Cells 1766.5.1 Formic Acid: Anodic Oxidation 1776.5.2 Cell Performance 1776.6 Borohydride Fuel Cells 1786.6.1 Anode Catalysts 1806.6.2 Challenges 1806.7 Application of Direct Liquid Fuel Cells 182Further Reading 1847 Phosphoric Acid Fuel Cells 1877.1 High- Temperature Fuel-Cell Systems 1877.2 System Design 1887.2.1 Fuel Processing 1887.2.2 Fuel Utilization 1897.2.3 Heat-Exchangers 1927.2.3.1 Designs 1937.2.3.2 Exergy Analysis 1937.2.3.3 Pinch Analysis 1947.3 Principles of Operation 1967.3.1 Electrolyte 1967.3.2 Electrodes and Catalysts 1987.3.3 Stack Construction 1997.3.4 Stack Cooling and Manifolding 2007.4 Performance 2017.4.1 Operating Pressure 2027.4.2 Operating Temperature 2027.4.3 Effects of Fuel and Oxidant Composition 2037.4.4 Effects of Carbon Monoxide and Sulfur 2047.5 TechnologicalDevelopments 204Further Reading 2068 Molten Carbonate Fuel Cells 2078.1 Principles of Operation 2078.2 Cell Components 2108.2.1 Electrolyte 2118.2.2 Anode 2138.2.3 Cathode 2148.2.4 Non-Porous Components 2158.3 Stack Configuration and Sealing 2158.3.1 Manifolding 2168.3.2 Internal and External Reforming 2188.4 Performance 2208.4.1 Influence of Pressure 2208.4.2 Influence of Temperature 2228.5 Practical Systems 2238.5.1 Fuel Cell Energy (USA) 2238.5.2 Fuel Cell Energy Solutions (Europe) 2258.5.3 Facilities in Japan 2288.5.4 Facilities in South Korea 2288.6 Future Research and Development 2298.7 Hydrogen Production and Carbon Dioxide Separation 2308.8 Direct Carbon Fuel Cell 231Further Reading 2349 Solid Oxide Fuel Cells 2359.1 Principles of Operation 2359.1.1 High-Temperature (HT) Cells 2359.1.2 Low-Temperature (IT) Cells 2379.2 Components 2389.2.1 Zirconia Electrolyte for HT-Cells 2389.2.2 Electrolytes for IT-Cells 2409.2.2.1 Ceria 2409.2.2.2 Perovskites 2419.2.2.3 Other Materials 2439.2.3 Anodes 2439.2.3.1 Nickel-YSZ 2439.2.3.2 Cathode 2459.2.3.3 Mixed Ionic–Electronic Conductor Anode 2469.2.4 Cathode 2479.2.5 Interconnect Material 2479.2.6 Sealing Materials 2489.3 Practical Design and Stacking Arrangements 2499.3.1 Tubular Design 2499.3.2 Planar Design 2519.4 Performance 2539.5 Developmental and Commercial Systems 2549.5.1 Tubular SOFCs 2559.5.2 Planar SOFCs 2569.6 Combined-Cycle and Other Systems 258Further Reading 26010 Fuels for Fuel Cells 26310.1 Introduction 26310.2 Fossil Fuels 26610.2.1 Petroleum 26610.2.2 Petroleum from Tar Sands, Oil Shales and Gas Hydrates 26810.2.3 Coal and Coal Gases 26810.2.4 Natural Gas and Coal-Bed Methane (Coal-Seam Gas) 27010.3 Biofuels 27210.4 Basics of Fuel Processing 27510.4.1 Fuel-Cell Requirements 27510.4.2 Desulfurization 27510.4.3 Steam Reforming 27710.4.4 Carbon Formation and Pre-Reforming 28010.4.5 Internal Reforming 28110.4.5.1 Indirect Internal Reforming (IIR) 28310.4.5.2 Direct Internal Reforming (DIR) 28310.4.6 Direct Hydrocarbon Oxidation 28410.4.7 Partial Oxidation and Autothermal Reforming 28510.4.8 Solar–Thermal Reforming 28610.4.9 Sorbent-Enhanced Reforming 28710.4.10 Hydrogen Generation by Pyrolysis or Thermal Cracking of Hydrocarbons 28910.4.11 Further Fuel Processing: Removal of Carbon Monoxide 29010.5 Membrane Developments for Gas Separation 29310.5.1 Non-Porous Metal Membranes 29310.5.2 Non-Porous Ceramic Membranes 29410.5.3 Porous Membranes 29410.5.4 Oxygen Separation 29510.6 Practical Fuel Processing: Stationary Applications 29510.6.1 Industrial Steam Reforming 29510.6.2 Fuel-Cell Plants Operating with Steam Reforming of Natural Gas 29610.6.3 Reformer and Partial Oxidation Designs 29810.6.3.1 Conventional Packed-Bed Catalytic Reactors 29810.6.3.2 Compact Reformers 29910.6.3.3 Plate Reformers and Microchannel Reformers 30010.6.3.4 Membrane Reactors 30110.6.3.5 Non-Catalytic Partial Oxidation Reactors 30210.6.3.6 Catalytic Partial Oxidation Reactors 30310.7 Practical Fuel Processing: Mobile Applications 30410.8 Electrolysers 30510.8.1 Operation of Electrolysers 30510.8.2 Applications 30710.8.3 Electrolyser Efficiency 31210.8.4 Photoelectrochemical Cells 31210.9 Thermochemical Hydrogen Production and Chemical Looping 31410.9.1 Thermochemical Cycles 31410.9.2 Chemical Looping 31710.10 Biological Production of Hydrogen 31810.10.1 Introduction 31810.10.2 Photosynthesis and Water Splitting 31810.10.3 Biological Shift Reaction 32010.10.4 Digestion Processes 320Further Reading 32111 Hydrogen Storage 32311.1 Strategic Considerations 32311.2 Safety 32611.3 Compressed Hydrogen 32711.3.1 Storage Cylinders 32711.3.2 Storage Efficiency 32911.3.3 Costs of Stored Hydrogen 33011.3.4 Safety Aspects 33011.4 Liquid Hydrogen 33111.5 Reversible Metal Hydrides 33311.6 Simple Hydrogen-Bearing Chemicals 33811.6.1 Organic Chemicals 33811.6.2 Alkali Metal Hydrides 33911.6.3 Ammonia, Amines and Ammonia Borane 34011.7 Complex Chemical Hydrides 34111.7.1 Alanates 34211.7.2 Borohydrides 34211.8 Nanostructured Materials 34411.9 Evaluation of Hydrogen Storage Methods 347Further Reading 35012 The Complete System and Its Future 35112.1 Mechanical Balance-of-Plant Components 35112.1.1 Compressors 35112.1.1.1 Efficiency 35412.1.1.2 Power 35612.1.1.3 Performance Charts 35612.1.1.4 Selection 35912.1.2 Turbines 36112.1.3 Ejector Circulators 36212.1.4 Fans and Blowers 36312.1.5 Pumps 36412.2 Power Electronics 36512.2.1 DC Regulators (Converters) and Electronic Switches 36612.2.2 Step-Down Regulators 36812.2.3 Step-Up Regulators 37012.2.4 Inverters 37112.2.4.1 Single Phase 37212.2.4.2 Three Phase 37612.2.5 Fuel-Cell Interface and Grid Connection Issues 37812.2.6 Power Factor and Power Factor Correction 37812.3 Hybrid Fuel-Cell + Battery Systems 38012.4 Analysis of Fuel-Cell Systems 38412.4.1 Well-to-Wheels Analysis 38512.4.2 Power-Train Analysis 38712.4.3 Life-Cycle Assessment 38812.4.4 Process Modelling 38912.4.5 Further Modelling 39212.5 Commercial Reality 39412.5.1 Back to Basics 39412.5.2 Commercial Progress 39512.6 Future Prospects: The Crystal Ball Remains Cloudy 397Further Reading 399Appendix 1 Calculations of the Change in Molar Gibbs Free Energy 401A1.1 Hydrogen Fuel Cell 401A1.2 Carbon Monoxide Fuel Cell 403Appendix 2 Useful Fuel-Cell Equations 405A2.1 Introduction 405A2.2 Oxygen and Air Usage 406A2.3 Exit Air Flow Rate 407A2.4 Hydrogen Usage 407A2.5 Rate of Water Production 408A2.6 Heat Production 409Appendix 3 Calculation of Power Required by Air Compressor and Power Recoverable by Turbine in Fuel-Cell Exhaust 411A3.1 Power Required by Air Compressor 411A3.2 Power Recoverable from Fuel-Cell Exhaust with a Turbine 412Glossary of Terms 415Index 437