Ishihara T. (Ed.) Perovskite Oxide for Solid Oxide Fuel Cells (Fuel Cells and Hydrogen Energy)
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6.7.2 Experiments and Data Processing. . . . . . . . . . . . . . . . . 138
6.7.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 138
6.8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
7 Perovskite Oxide for Cathode of SOFCs ...................... 147
Tatsuya Kawada
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
7.2 Properties Required for a Cathode Material . . . . . . . . . . . . . . 148
7.2.1 Catalytic Activity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
7.2.2 Electronic Conductivity. . . . . . . . . . . . . . . . . . . . . . . . . 149
7.2.3 Oxygen Transport (Bulk or Surface). . . . . . . . . . . . . . . 151
7.2.4 Chemical Stability and Compatibility . . . . . . . . . . . . . . 152
7.2.5 Morphological Stability. . . . . . . . . . . . . . . . . . . . . . . . . 152
7.3 General Description of Cathode Reaction and Polarization . . 153
7.3.1 Oxygen Electrode Process . . . . . . . . . . . . . . . . . . . . . . . 153
7.3.2 Equivalent Circuit for a Cathode–Electrolyte
Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
7.4 Cathode for High-Temperature SOFC: (La, Sr)MnO
3
...... 156
7.4.1 Transport Properties and Electrochemical
Reaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
7.4.2 Chemical and Morphological Stability of LSM . . . . . . 158
7.5 Cathode for Intermediate-Temperature SOFC:
(La, Sr)CoO
3
, (La, Sr)(Co, Fe)O
3
...................... 160
7.5.1 General Features of Co-Based Perovskite Cathode . . . 160
7.5.2 Electrochemical Reaction of a Model Electrode:
A (La,Sr)CoO
3
Dense Film . . . . . . . . . . . . . . . . . . . . . . 161
7.5.3 Electrochemical Response of (La, Sr)CoO
3
on Zirconia with and Without Ceria Interlayer . . . . . . 163
7.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
8 Perovskite Oxide Anodes for SOFCs......................... 167
J. T. S. Irvine
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
8.2 Anode Materials for SOFCs . . . . . . . . . . . . . . . . . . . . . . . . . . 168
8.3 Perovskite Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
8.4 Doping, Nonstoichiometry, and Conductivity. . . . . . . . . . . . . 170
8.5 Perovskite Anode Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
8.6 A(B,B
0
)O
3
Perovskites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
8.7 Tungsten Bronze Anode Materials. . . . . . . . . . . . . . . . . . . . . . 178
8.8 Anode Materials for All-Perovskite Fuel Cells . . . . . . . . . . . . 179
8.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
x Contents
9 Intermediate-Temperature Solid Oxide Fuel Cells Using
LaGaO
3
............................................... 183
Taner Akbay
9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
9.2 Cell Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
9.2.1 Electrolyte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
9.2.2 Anode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
9.2.3 Cathode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
9.3 Stack Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
9.4 Module Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
9.4.1 A 1-kW Class Single-Stack Module . . . . . . . . . . . . . . . 192
9.4.2 A 10-kW Class Multi-Stack Module . . . . . . . . . . . . . . . 195
9.5 System Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
9.6 Stack Modeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
10 Quick-Start-Up Type SOFC Using LaGaO
3
-Based New
Electrolyte ............................................. 205
Akira Kawakami
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
10.2 Micro-Tubular Cell Development . . . . . . . . . . . . . . . . . . . . . 206
10.3 Rapid Thermal Cycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
10.4 Fuel Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
10.5 Stack Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
10.6 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
11 Proton Conductivity in Perovskite Oxides ..................... 217
Truls Norby
11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
11.2 Proton Conductivity in Acceptor-Doped Perovskites . . . . . . 219
11.2.1 Protons in Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
11.2.2 Hydration of Acceptor-Doped Perovskites . . . . . . . . . 219
11.2.3 Proton Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
11.2.4 Charge Mobility and Conductivity of Protons . . . . . . 224
11.2.5 Proton Conductivity in Acceptor-Doped Simple
Perovskites, ABO
3
............................ 225
11.2.6 Effects of Defect–Acceptor Interactions . . . . . . . . . . . 228
11.2.7 Grain Boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
11.3 Proton Conduction in Inherently Oxygen-Deficient
Perovskites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
11.3.1 Hydration of Ordered Oxygen Deficiency. . . . . . . . . . 230
11.3.2 Nomenclature and Hydration of Disordered
Intrinsic Oxygen Deficiency. . . . . . . . . . . . . . . . . . . . . 231
Contents xi
11.3.3 Order–Disorder Reactions Involving Hydrated
Inherently Oxygen-Deficient Perovskites
(Oxyhydroxides) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
11.4 Hydration of Undoped Perovskites . . . . . . . . . . . . . . . . . . . . 233
11.5 Proton Conductivity in Selected Classes Of Non-Perovskite
Oxides and Phosphates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
11.6 Developments of Proton-Conducting SOFCs . . . . . . . . . . . . 236
11.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
12 Proton Conduction in Cerium- and Zirconi um-Based Perovskite
Oxides ................................................ 243
Hiroshige Matsumoto
12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
12.2 Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
12.3 Activation/Deactivation of Electrodes . . . . . . . . . . . . . . . . . . 247
12.4 Stability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
12.5 Dopant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
12.6 Proton Hole Mixed Conduction. . . . . . . . . . . . . . . . . . . . . . . 255
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
13 Mechanisms of Proton Conduction in Perovskite-Type
Oxides ................................................ 261
K. D. Kreuer
13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
13.2 Proton Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
13.3 Mechanisms of Proton Conduction (Undoped, Cubic
Perovskites). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
13.4 Complications (Symmetry Reduct ion, Dop ing, Mixed
Site Occupancy) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
13.5 Implications for the Development of Proton-Conducting
Electrolytes for Fuel Cell Applications . . . . . . . . . . . . . . . . . 270
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
14 Intermediate-Temperature SOFCs Using Proton-Conducting
Perovskite ............................................. 273
Naoki Ito
14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
14.2 Preparation of Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
14.3 Characterization of Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . 277
14.4 Operation and Evaluation of Fuel Cells. . . . . . . . . . . . . . . . . 279
14.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
xii Contents
15 LaCrO
3
-Based Perovskite for SOFC Interconnects.............. 285
Teruhisa Horita
15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
15.2 Sintering Properties and Chemical Compatibility
with the Other Components . . . . . . . . . . . . . . . . . . . . . . . . . . 286
15.3 Electronic Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
15.4 Defect Chemistry and Oxygen Electrochemical Leak . . . . . . 289
15.5 Lattice Expansion During Reduction and Temperature
Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
15.6 Mechanical Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
15.7 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
Index ..................................................... 297
Contents xiii
Contributors
Taner Akbay Mitsubishi Materials Corporation, Central Research Institute,
1002-14, Mukaiyama, Naka-shi, Ibaraki, 311-0102, Japan, akbay@mmc.co.jp
A. Berenov Department of Materials, Imperial College, London, London SW7
2AZ, UK, a.berenov@imperial.ac.jp
Teruhisa Horita National Institute of Advanced Industrial Science and
Technology (AIST), AIST Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki
305-8565, Japan, t.horita@aist.go.jp
J.T.S. Irvine School of Chemistry, University of St-Andrews, Fife, Scotland
KY16 9ST, UK, jtsi@s t-and.ac.uk
Tatsumi Ishihara Department of Applied Chemistry, Faculty of Engineering,
Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan,
ishihara@cstf.kyushu-u.ac.jp.
Naoki Ito Fuel Cell System Development Division, Toyota Motor
Corporation, 1200 Mishuku, Susono, Shizuoka 410-1193, Japan,
naoki@ito.tec.toyota.co.jp
Hiroyasu Iwahara Nagoya University, Furo-cho, Chigusaku, Nagoya,
464-8601, Japan, iwahara-h@m3.gyao.ne.jp
Tatsuya Kawada Graduate School of Envi ronmental Studies, Tohoku
University, 1-1 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan,
kawada@ee.mech.to hoku.ac.jp
Akira Kawakami TOTO Ltd., Chigasaki, Kanagawa 253-8577, Japan,
akira.kawakami@toto.co.jp
J.A. Kilner Department of Materials, Imperial College, London, London SW7
2AZ, UK, j.kilner@imperial.ac.uk
K.D. Kreuer Max-Planck-Institut fu
¨
r Festk
¨
orperforschung, Heisenbergstr. 1,
D-70569 Stuttgart, Germany, Kreuer@fkf.mpg.de
xv
Hiroshige Matsumoto INAMORI Frontier Research Center, Kyushu
University, 744 Motooka, Nishiku, Fukuoka 819–0395, Japan,
matsumoto@ifrc.kyushu-u.ac.jp
Truls Norby Department of Chemistry, Centre for Mater ials Science and
Nanotechnology, University of Oslo, FERMiO, Gaustadalle
´
en 21, NO-0349
Oslo, Norway, t.e.norby@kjemi.uio. no
J. Rossiny Department of Materials, Imperial College, London, London SW7
2AZ, UK, a.berenov@imperial.ac.jp
Masatomo Yashima Tokyo Institute of Technology, Yokohama 226–8502,
Japan, yashima@materia.titech.ac.jp
Harumi Yokokawa Energy Technology Research Institute, National Institute
of Advanced Industrial Science and Techno logy, Higa shi 1-1-1, AIST Central
No.5, Tsukuba, Ibaraki 305-8565, Japan, h-yokokawa@aist.go.jp
xvi Contributors
Chapter 1
Structure and Properties of Perovskite Oxides
Tatsumi Ishihara
1.1 Introduction
Oxide groups consisting of two or more different cations are called complex or
mixed oxides, and many types of structures are known that are different from those
of the simple oxides. In some special cases, oxides consisting of a single cation in
different oxidation states are also classified as mixed oxides. For example, Eu
3
O
4
,
a mixed oxide, consists of Eu(III) and Eu(II) in 6- or 8-coordination, respectively.
However, the most typical structure of a mixed oxide consists simply of two or
more different cations with different oxidation states, ionic radii, and coordination
numbers. This diversity, which comes from the complexity of these structures,
results in a larger number of different properties as compared to those of simple
oxides. One of the most well known and important complex oxide structures is the
spinel structure (AB
2
O
4
), which shows important magnetic properties. The struc-
ture of such oxides displays a most interesting complexity. Because the A and B
ions in this structure are close in size, oxides of this type are typical examples of the
versatility of mixed oxides. In the ideal case, one sixfold-coordinated ion occupies
the A site and another sixfold-coordinated cation occupies the B site; however, in
some cases, mixing of cations on A- and B-site ions occurs. In the most complex
case of the spinel structure, the same cations occupy both sites with the structure in
different environments. Therefore, a unique feature of mixed oxide compounds is
the display of a variety of properties that are partially the result of the variety of the
structures. In particular, among mixed oxides, the perovskite oxides are well
known for displaying a multitude of structures and properties, which are briefly
introduced in this chapter.
T. Ishihara (*)
Department of Applied Chemistry, Faculty of Engineering, Kyushu University,
Motooka 744, Nishi-ku, Fukuoka, 819-0395, Japan
e-mail: ishihara@cstf.kyushu-u.ac.jp
T. Ishihara (ed.), Perovskite Oxide for Solid Oxide Fuel Cells,
Fuel Cells and Hydrogen Energy, DOI 10.1007/978-0-387-77708-5_1,
Ó Springer ScienceþBusiness Media, LLC 2009
1
1.2 Structure of Perovskite Oxides
The typical chemical formula of the perovskite structure is ABO
3
, where A and
B denote two different cations. The ilmenite structure has the same composition
as the perovskite one, i.e., ABO
3
; however, A and B in this structure are cations
of approximately the same size that occupy an octahedral site. Therefore, in
spite of the fact that they share the same general chemical formula, structures
classified as ilumenite or ilmenite-related structure (e.g., LiSbO
3
) are different
from perovskite.
Perovskite oxides comprise large families among the structures of oxide
compounds, and several perovskite-related structures are currently recognized.
Typical structures consist of large-sized 12-coordinated cations at the A site and
small-sized 6-coordinated cations at the B site. Several complex halides and
sulfides and many complex oxides have a perovskite struc ture. In particular,
(Mg,Fe)SiO
3
or CaSiO
3
is thought to be the predominant compound in the
geosphere [1, 2]. Perovskite compounds with different combinations of charged
cations in the A and B sites, e.g., 1 þ5, 2 þ4, and 3 þ3, have been discovered.
Even more complex combinations are observed, such as Pb(B’
1/2
B’’
1/2
)O
3
,
where B’ ¼Sc, Fe and B’’ ¼Nb, Ta, or La(B’
1/2
B’’
1/2
)O
3
, where B’ ¼Ni, Mg,
etc., and B’’ ¼Ru(IV) or Ir(IV). In addition, many ABO
3
compounds crystallize
in polymorphic structures, which show only a small distortion from the most
symmetrical form of the perovskite structure.
The ideal structure of perovskite, which is illustrated in Fig. 1.1, is a cubic
lattice. Although few compounds have this ideal cubic structure, many oxides
have slightly distorted variants with lower symmetry (e.g., hexagonal or orthor-
hombic). Furthermore, even though some compounds have ideal cubic structure,
many oxides display slightly distorted variants with lower symmetry. Several
examples of perovskite oxides are listed in Table 1.1, where it is clear that a large
number of perovskite oxides have a rhombohedral lattice. Additionally, in many
compounds a large extent of oxygen or cation deficiency has been observed.
Because of the large lattice energy, many compounds are classified as perovskite
oxides in spite of the large cation and/or oxygen deficiencies. There are various
types of distortions in the perovskite structure that have strongly related to their
properties, in particular, their ferromagnetic or ferroelectric properties.
O
B ion
A ion
Fig. 1.1 Ideal perovskite
structure
2 T. Ishihara
To understand the deviations from the ideal cubic structure, these ABO
3
oxides are first regarded as purely ionic crystals. In the case of the ideal structure,
the following relationship between the radii of the A, B, and O
2–
ions holds true:
r
A
þ r
O
¼
ffiffiffi
2
p
ðr
B
þ r
O
Þ
Therefore, the deviation from the ideal structure in perovskite oxides can be
expressed through the following so-called tolerance factor, t:
t ¼ðr
A
þ r
O
Þ=
ffiffiffi
2
p
ðr
B
þ r
O
Þ
In perovskite-type compounds, the value of t lies between approximately
0.80 and 1.10. It is noted that the oxides with the lower t values crystallize in the
ilmenite structure, which is a polymorph of the perovskite structure. It seems
superfluous to say that for the ideal cubic structure the value of t is close to 1 or
at least greater than 0.89. Figure 1.2 shows the crystal groups for A
2þ
B
4þ
O
3
and A
3þ
B
3þ
O
3
combinations, which are related to deviation from the ideal
structure [3]. As the value of t decreases, the structure of the unit lattice is shifted
Table 1.l Typical perovskite compounds
Compound Lattice parameter/x10 nm
abc
Cubic structure
KTaO
3
3.989
NaTaO
3
3.929
NaNbO
3
3.949
BaMnO
3
4.040
BaZrO
3
4.193
SrTiO
3
3.904
KMnF
3
4.189
KFeF
3
4.121
Tetragonal structure
BiAIO
3
7.61 7.94
PbSnO
3
7.86 8.13
BaTiO
3
3.994 4.038
PdTiO
3
3.899 4.153
TIMnCl
3
5.02 5.04
LaAIO3 type
LaAIO
3
5.357 a ¼608 06’
LaNiO
3
5.461 a ¼608 05’
BiFeO
3
5.632 a ¼608 06’
KNbO
3
4.016 a ¼608 06’
GdFeO
3
type
GdFeO
3
5.346 5.616 7.668
YFeO
3
5.283 5.592 7.603
NdGaO
3
5.426 5.502 7.706
CaTiO
3
5.381 5.443 7.645
NaMgF
3
5.363 5.503 7.676
1 Structure and Properties of Perovskite Oxides 3
from cubic to triclinic as a result of the increased distortions. Figure 1.3 shows
chemical elements that can be accommodated within the perovskite structure. It
is evident that almos t all elements except for noble gases can occupy eithe r A or
B lattice positions in the perovskite lattice, including dopants. The stabili ty and
the crystal group are mainly determined by the ratio of the ionic radii of the
A and B cations. Indeed, the structure is dependent not only on the size but also
on the nature of the A and B atoms. For example, AMnO
3
compounds crystal-
lize in the perovskite structure when the A cation is La or Ce-Dy, whereas a new
hexagonal structure with 5- and 7-coordination of Mn and A, respectively, is
formed when A ¼Ho-Lu or Y if A ¼La or Ce-Dy [4]. Here, attention should be
paid to the nature of the B atom, where the nature of the bond is highly
cubic tetragonal
pseudo
cubic
pseudo
cubic
orthorhombic
rhombo
hedral
-
rhombo-
hedral
orthorhombic
Tl
2
O
3
type
corundum
La
2
O
3
type
A
2+
B
4+
O
3
A
3+
B
3+
O
3
perovskite
0.55
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
Mn
4+
V
4+
Ti
4+
SrVO
3
c
a
<1
Sn
4+
Hf
4+
Zr
4+
Ce
4+
U
4+
Th
4+
Ba
2+
Al
3+
Ga
3+
Fe
3+
Cr
3+
Ti
3+
Sc
3+
Nd
3+
In
3+
Y
3+
Sm
3+
Ce
3+
La
3+
La
3+
Ce
3+
Nd
3+
Sm
3+
Y
3+
In
3+
Sc
3+
Fe
3+
Ca
3+
Cr
3+
Al
3+
Pb
2+
Eu
2+
Sr
2+
Ca
2+
Cd
2+
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30
c
a
>1
Fig. 1.2 The effect of ionic size of A- and B-site cations on the observed distortions of the
perovskite structure
Fig. 1.3 Chemical elements that can occupy sites in the perovskite structure
4 T. Ishihara