Perovskite oxide for solid oxide fuel cells

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.

Tatsumi lshiharaHarumi YokokawaHiroyasu IwaharaTatsumi IshiharaJ. A. Kilner and A. Berenov and J. RossinyMasatomo YashimaTatsuya KawadaJ. T. S. IrvineTaner AkbayAkira KawakamiTruls NorbyHiroshige MatsumotoK. D. KreuerNaoki ItoTeruhisa Horita

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

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