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Summary
Summary
Fuel cell technology is quite promising for conversion of chemical energy of hydrocarbon fuels into electricity without forming air pollutants. There are several types of fuel cells: polymer electrolyte fuel cell (PEFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), and alkaline fuel cell (AFC). Among these, SOFCs are the most efficient and have various advantages such as flexibility in fuel, high reliability, simple balance of plant (BOP), and a long history. Therefore, SOFC technology is attracting much attention as a power plant and is now close to marketing as a combined heat and power generation system. From the beginning of SOFC development, many perovskite oxides have been used for SOFC components; for example, LaMnO -based oxide for the cathode and 3 LaCrO for the interconnect are the most well known materials for SOFCs. The 3 current SOFCs operate at temperatures higher than 1073 K. However, lowering the operating temperature of SOFCs is an important goal for further SOFC development. Reliability, durability, and stability of the SOFCs could be greatly improved by decreasing their operating temperature. In addition, a lower operating temperature is also beneficial for shortening the startup time and decreasing energy loss from heat radiation. For this purpose, faster oxide ion conductors are required to replace the conventional Y O -stabilized ZrO 2 3 2 electrolyte. A new class of electrolytes such as LaGaO is considered to be 3 highly useful for intermediate-temperature SOFCs.
Table of Contents
1 Structure and Properties of Perovskite Oxides | p. 1 |
1.1 Introduction | p. 1 |
1.2 Structure of Perovskite Oxides | p. 2 |
1.3 Typical Properties of Perovskite Oxides | p. 7 |
1.4 Preparation of Perovskite Oxide | p. 12 |
1.5 Perovskite Oxides for Solid Oxide Fuel Cells (SOFCs) | p. 15 |
References | p. 16 |
2 Overview of Intermediate-Temperature Solid Oxide Fuel Cells | p. 17 |
2.1 Introduction | p. 17 |
2.2 Characteristic Features of Solid Oxide Fuel Cells | p. 18 |
2.2.1 Merits and Demerits of SOFCs | p. 18 |
2.2.2 Issues for Intermediate-Temperature SOFCs | p. 20 |
2.2.3 Stack Design | p. 35 |
2.3 Development of Intermediate Temperature SOFC Stacks/Systems | p. 36 |
2.3.1 Kyocera/Osaka Gas | p. 36 |
2.3.2 Mitsubishi Materials Corporation | p. 37 |
2.3.3 Micro SOFCs by TOTO | p. 38 |
2.4 Perspective | p. 38 |
2.4.1 Applications | p. 38 |
2.4.2 Fuel Flexibility and Reliability in Relationship to Intermediate-Temperature SOFCs | p. 41 |
2.4.3 Hybrid Systems | p. 41 |
2.5 Summary | p. 42 |
References | p. 42 |
3 Ionic Conduction in Perovskite-Type Compounds | p. 45 |
3.1 Introduction | p. 45 |
3.2 Conduction Behavior of Perovskite-Type Compounds | p. 46 |
3.3 Early Studies on Ionic Conduction in Perovskite-TypeOxides | p. 49 |
3.4 Oxide Ion Conduction | p. 52 |
3.5 Proton Conduction | p. 55 |
3.6 Lithium Ion Conduction | p. 59 |
3.7 Halide Ion Conduction | p. 60 |
3.8 Silver Ion Conduction | p. 61 |
References | p. 62 |
4 Oxide Ion Conductivity in Perovskite Oxide for SOFC Electrolyte | p. 65 |
4.1 Introduction | p. 65 |
4.2 Oxide Ion Conductivity in Oxide | p. 66 |
4.3 Oxide Ion Conductivity in Perovskite Oxides | p. 68 |
4.4 LaGa03-Based Oxide Doped with Sr and Mg (LSGM)as a New Oxide Ion Conductor | p. 71 |
4.4.1 Effects of Dopant for La and Ga Site | p. 71 |
4.4.2 Transition Metal Doping Effects on Oxide Ion Conductivity in LSGM | p. 74 |
4.5 Basic Properties of the LSGM Electrolyte System | p. 77 |
4.5.1 Phase Diagram of La-Sr-Ga-Mg-0 | p. 77 |
4.5.2 Reactivity with SOFC Component | p. 77 |
4.5.3 Thermal Expansion Behavior and Other Properties | p. 78 |
4.5.4 Behavior of Minor Carrier | p. 79 |
4.5.5 Diffusivity of Oxide Ion | p. 82 |
4.6 Performance of a Single Cell Using LSGM Electrolyte | p. 84 |
4.7 Preparation of LaGa03 Thin-Film Electrolytes for Application at Temperatures Lower Than 773 K | p. 87 |
4.8 Oxide Ion Conductivity in the Perovskite-Related Oxides | p. 89 |
4.9 Summary | p. 92 |
References | p. 92 |
5 Diffusivity of the Oxide Ion in Perovskite Oxides | p. 95 |
5.1 Introduction | p. 95 |
5.1.1 Definitions of Diffusion Coefficients | p. 96 |
5.1.2 The Oxygen Tracer Diffusion Coefficient | p. 96 |
5.1.3 The Surface Exchange Coefficient | p. 98 |
5.1.4 Defect Chemistry and Oxygen Transport | p. 99 |
5.1.5 Defect Equilibria | p. 99 |
5.2 Diffusion in Mixed Electronic-Ionic Conducting Oxides (MEICs) | p. 102 |
5.2.1 Effect of A-Site Cation on Oxygen Diffusivity | p. 103 |
5.2.2 The Effect of B-Site Cation on Oxygen Diffusivity | p. 104 |
5.2.3 The Effect of A-Site Cation Vacancies on Oxygen Diffusivity | p. 105 |
5.2.4 Temperature Dependence of the Oxygen Diffusion Coefficient | p. 105 |
5.2.5 The Effect of Oxygen Pressure | p. 108 |
5.3 Oxygen Diffusion in Ionic Conducting Perovskites | p. 108 |
5.4 Oxygen Diffusion in Perovskite-Reiated Materials | p. 110 |
5.5 Correlations Between Oxygen Diffusion Parameters | p. 110 |
5.6 Conclusions | p. 112 |
References | p. 113 |
6 Structural Disorder, Diffusion Pathway of Mobile Oxide Ions, and Crystal Structure in Perovskite-Type Oxides and Related Materials | p. 117 |
6.1 Introduction | p. 117 |
6.2 High-Temperature Neutron Powder Diffractometry | p. 118 |
6.3 Data Processing for Elucidation of the Diffusion Paths of Mobile Oxide Ions in Ionic Conductors: Rietveld Analysis, Maximum Entropy Method (MEM), and MEM-Based Pattern Fitting (MPF) | p. 120 |
6.4 Diffusion Path of Oxide Ions in the Fast Oxide Ion Conductor (La0.8Sr0.2)(Ga0.8Mg0.15Co0.05)O2.8 [10] | p. 121 |
6.4.1 Introduction | p. 121 |
6.4.2 Experiments and Data Processing | p. 121 |
6.4.3 Results and Discussion | p. 122 |
6.5 Diffusion Path of Oxide Ions in an Oxide Ion Conductor, La0.64(Ti0.92Nb0.08)O2.99, with a Double Perovskite-Type Structure [11] | p. 126 |
6.5.1 Introduction | p. 126 |
6.5.2 Experiments and Data Processing | p. 126 |
6.5.3 Results and Discussion | p. 127 |
6.6 Crystal Structure and Structural Disorder of Oxide Ions in Cathode Materials, Lao.6Sro.4CoO3-? and La0.6Sr0.4Co0.8Fe0.2O3-?, with a Cubic Perovskite-Type Structure [12, 13] | p. 131 |
6.6.1 Introduction | p. 131 |
6.6.2 Experiments and Data Processing | p. 131 |
6.6.3 Results and Discussion | p. 132 |
6.7 Structural Disorder and Diffusion Path of Oxide Ions in a Doped Pr2Ni04-Based Mixed Ionic-Electronic Conductor (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4 + ? with a K2NiF4-Type Structure [15] | p. 137 |
6.7.1 Introduction | p. 137 |
6.7.2 Experiments and Data Processing | p. 138 |
6.7.3 Results and Discussion | p. 138 |
6.8 Conclusions | p. 141 |
References | p. 143 |
7 Perovskite Oxide for Cathode of SOFCs | p. 147 |
7.1 Introduction | p. 147 |
7.2 Properties Required for a Cathode Material | p. 148 |
7.2.1 Catalytic Activity | p. 148 |
7.2.2 Electronic Conductivity | p. 149 |
7.2.3 Oxygen Transport (Bulk or Surface) | p. 151 |
7.2.4 Chemical Stability and Compatibility | p. 152 |
7.2.5 Morphological Stability | p. 152 |
7.3 General Description of Cathode Reaction and Polarization | p. 153 |
7.3.1 Oxygen Electrode Process | p. 153 |
7.3.2 Equivalent Circuit for a Cathode-Electrolyte Interface | p. 154 |
7.4 Cathode for High-Temperature SOFC: (La, Sr)Mn03 | p. 156 |
7.4.1 Transport Properties and Electrochemical Reaction | p. 156 |
7.4.2 Chemical and Morphological Stability of LSM | p. 158 |
7.5 Cathode for Intermediate-Temperature SOFC: (La, Sr)Co03, (La, Sr)(Co, Fe)03 | p. 160 |
7.5.1 General Features of Co-Based Perovskite Cathode | p. 160 |
7.5.2 Electrochemical Reaction of a Model Electrode: A (La,Sr)Co03 Dense Film | p. 161 |
7.5.3 Electrochemical Response of (La, Sr)Co03 on Zirconia with and Without Ceria Interlayer | p. 163 |
7.6 Summary | p. 164 |
References | p. 165 |
8 Perovskite Oxide Anodes for SOFCs | p. 167 |
8.1 Introduction | p. 167 |
8.2 Anode Materials for SOFCs | p. 168 |
8.3 Perovskite Chemistry | p. 169 |
8.4 Doping, Nonstoichiometry, and Conductivity | p. 170 |
8.5 Perovskite Anode Materials | p. 173 |
8.6 A(B,B')03 Perovskites | p. 177 |
8.7 Tungsten Bronze Anode Materials | p. 178 |
8.8 Anode Materials for All-Perovskite Fuel Cells | p. 179 |
8.9 Conclusions | p. 180 |
References | p. 180 |
9 Intermediate-Temperature Solid Oxide Fuel Cells Using LaGa03 | p. 183 |
9.1 Introduction | p. 183 |
9.2 Cell Development | p. 184 |
9.2.1 Electrolyte | p. 184 |
9.2.2 Anode | p. 185 |
9.2.3 Cathode | p. 188 |
9.3 | p. 190 |
9.4 | p. 192 |
9.4.1 A 1-kW Class Single-Stack Module | p. 192 |
9.4.2 A 10-kW Class Multi-Stack Module | p. 195 |
9.5 System Development | p. 196 |
9.6 Stack Modeling | p. 198 |
References | p. 202 |
10 Quick-Start-Up Type SOFC Using LaGa03-Based New Electrolyte | p. 205 |
10.1 Introduction | p. 205 |
10.2 Micro-Tubular Cell Development | p. 206 |
10.3 Rapid Thermal Cycling | p. 211 |
10.4 Fuel Flexibility | p. 211 |
10.5 Stack Development | p. 214 |
10.6 Summary | p. 216 |
References | p. 216 |
11 Proton Conductivity in Perovskite Oxides | p. 217 |
11.1 Introduction | p. 217 |
11.2 Proton Conductivity in Acceptor-Doped Perovskites | p. 219 |
11.2.1 Protons in Oxides | p. 219 |
11.2.2 Hydration of Acceptor-Doped Perovskites | p. 219 |
11.2.3 Proton Diffusion | p. 222 |
11.2.4 Charge Mobility and Conductivity of Protons | p. 224 |
11.2.5 Proton Conductivity in Acceptor-Doped Simple Perovskites, AB03 | p. 225 |
11.2.6 Effects of Defect-Acceptor Interactions | p. 228 |
11.2.7 Grain Boundaries | p. 229 |
11.3 Proton Conduction in Inherently Oxygen-Deficient Perovskites | p. 230 |
11.3.1 Hydration of Ordered Oxygen Deficiency | p. 230 |
11.3.2 Nomenclature and Hydration of Disordered Intrinsic Oxygen Deficiency | p. 231 |
11.3.3 Order-Disorder Reactions Involving Hydrated Inherently Oxygen-Deficient Perovskites (Oxyhydroxides) | p. 232 |
11.4 Hydration of Undoped Perovskites | p. 233 |
11.5 Proton Conductivity in Selected Classes Of Non-Perovskite Oxides and Phosphates | p. 233 |
11.6 Developments of Proton-Conducting SOFCs | p. 236 |
11.7 Conclusions | p. 237 |
References | p. 238 |
12 Proton Conduction in Cerium- and Zirconium-Based Perovskite Oxides | p. 243 |
12.1 Introduction | p. 243 |
12.2 Conductivity | p. 245 |
12.3 Activation/Deactivation of Electrodes | p. 247 |
12.4 Stability | p. 248 |
12.5 Dopant | p. 251 |
12.6 Proton Hole Mixed Conduction | p. 255 |
References | p. 258 |
13 Mechanisms of Proton Conduction in Perovskite-Type Oxides | p. 261 |
13.1 Introduction | p. 261 |
13.2 Proton Sites | p. 262 |
13.3 Mechanisms of Proton Conduction (Undoped, Cubic Perovskites) | p. 264 |
13.4 Complications (Symmetry Reduction, Doping, Mixed Site Occupancy) | p. 268 |
13.5 Implications for the Development of Proton-Conducting Electrolytes for Fuel Cell Applications | p. 270 |
References | p. 271 |
14 Intermediate-Temperature SOFCs Using Proton-Conducting Perovskite | p. 273 |
14.1 Introduction | p. 273 |
14.2 Preparation of Fuel Cells | p. 277 |
14.3 Characterization of Fuel Cells | p. 277 |
14.4 Operation and Evaluation of Fuel Cells | p. 279 |
14.5 Conclusion | p. 282 |
References | p. 283 |
15 LaCr03-Based Perovskite for SOFC Interconnects | p. 285 |
15.1 Introduction | p. 285 |
15.2 Sintering Properties and Chemical Compatibility with the Other Components | p. 286 |
15.3 Electronic Conductivity | p. 287 |
15.4 Defect Chemistry and Oxygen Electrochemical Leak | p. 289 |
15.5 Lattice Expansion During Reduction and Temperature Change | p. 293 |
15.6 Mechanical Strength | p. 293 |
15.7 Summary | p. 294 |
References | p. 295 |
Index | p. 297 |