SOFC. (Solid Oxide Fuel Cell, SOFC) Co 0.2 Fe 0.8 O 3- (LSCF) Shao Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3- (BSCF). 8,9) . 1) SOFC

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1 (Solid Oxide Fuel Cell, SOFC). 1) SOFC ,2,3-5) SOFC SOFC. (Intermediate Temperature-operating Solid Oxide Fuel Cell, IT-SOFC) 700. SOFC Fig. 1 ABO 3 SOFC. SOFC simple perovskite A B-site (A-site : lanthanide Sr, B-site : transition metal),. 6,7) IT - SOFC Steele Bae La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3- (LSCF) Shao Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3- (BSCF). 8,9) (mixed ionic and electronic conductor, MIEC) IT-SOFC. 8,9) Complex perovskite IT-SOFC (disordering) (coulomb potential), (elastic potential) (mobility). 10) Imperial college John Killer GdBaCo 2 O 5+ layered perovskite IT-SOFC. 11) oxygen deficient complex perovksite layered perovskite. 24

2 2.1. Complex perovskite layered perovskite Fig. 1 ABO 3 Spinel, complex perovskite layered perovskite. ABO 3 simple perovskite cubic A-site,,,. A-site 12 (Coordination Number, CN) B-site Co Fe simple perovskite A-site B-site complex perovskite A-site Sr (BO 6 ) 8. ABO 3 perovskite 90% A-site B-site perovskite simple perovskite A-site La Sr complex perovskite. La 1- xsr x CoO 3 A-site Co d. LSCF A-site La Sr B-site Co Fe complex perovskite. perovskite Sr Co. La 1-x Sr x Co 0.2 Fe 0.8 O 3- Sr 20 mol% orthorhombic La Sr rhombohedral cubic. 13) LSCF Sr rhombohedral rhombohedral cubic. 14) A / A // B 2 O 5+ (colossal magneto resistance, CMR). oxy-. 12) La 1-x Sr x CoO 3 (LSC) La 1-x Sr x Co 1-y Fe y O 3- (LSCF). LSC Fig. 1. Various cathode materials for SOFC. Fig. 2. Ordering of lanthanide A / and alkali-earth A // ions in the A-site sublattice of half-doped perovskites. (a) A simple cubic perovskite A / 0.5A // 0.5BO 3 (B is transition metal) with random occupation of A-sites is transformed into (b) a layered crystal A / A // B 2 O 6 by doubling the unit cell, provided the difference in ionic radii of A / and A // ions is sufficiently large. (c) Oxygen atoms can be partially or completely removed from lanthanide planes, providing a variability of the oxygen content in A / A // B2O5+, where 0< <1. 10) 25

3 gen ion diffusivity surface exchange coefficient SOFC IT-SOFC 11, 15-20). A / A // B 2 O 5+ layered perovkite double layered perovskite A-site ordering. ABO 3 A-site oxygen disordering. layered perovskite Taskin GdBaMnO 5+ (cation sublattice) ordering oxygen transport oxygen uptake. 10,16) Fig ) Fig. 2 A / 0.5A // 0.5BO 3 Fig. 2(a) simple cubic perovskite Fig. 2(b) A / A // B 2 O 6 layered perovskite. Fig. 2(c) A / A // B 2 O 6 Ln A / A // B 2 O 5+ layered perovskite. B-site. B-site Mn A- site ordering disordering. B-site Co Mn ordering. Table 2. The Relation of Oxygen Content and Physical-chemical in LnBaCo 2 O 5+ Oxygen Charge Distribution The ionic content state of of various State radii of Co-O bond distance Cell volume ( ) Co Co state Co Co 2+ :50% Co 3+ :50% -Charge ordering of Co 3+ and Co 2 24,27) Co 3+ :100% -MIT (Metal-Insulation Transition) 1)Different Ln 23) 2)Spin-state transition of Co in octahedral place 28,29) layered perovskite LnBaCo 2 O 5+ Ln Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho Y lanthanide. 11,21-26) LnBaCo 2 O 5+ layered perovskite lanthanide tetragonal orthorhombic. Table 1 Tb, Dy Ho Pr Nd 2.2. Layered perovskite Table 1. The Relation of Compositions and their Structures with Respect to the Various Types of Lanthanides Structure PrBaCo 2 O 5+ Tetragonal NdBaCo 2 O 5+ Tetragonal SmBaCo 2 O 5+ Orthorhombic GdBaCo 2 O 5+ Orthorhombic Fig. 3. Crystal structure of the ordered LnBaCo2O5+ 26). 26

4 Table 3. LnBaCo 2 O 5+ Type Cathode Materials -Power density: 150 and 250 mw.cm -2 at 700 and 800 ) from the samples of GdBaCo 2O 5+ /YSZ/Ni-YSZ GdBaCo 2O 5+ 35) -Advanced power density: 300, 500 and 550 mw.cm -2 at 700, 800 and 900 from the samples of GdBaCo 2O 5+ /porous YSZ layer/ysz/ni-ysz properties -Decomposition of GdBaCo 2O 5+ under 500 ppm to 100% CO 2 -Stability under air condition for 100 hours at 500, 600 and 700 GdBaCo 2O 5+ -Reactivity with various electrolytes 36) -Area specific resistance (ASR): cm 2 at 650 on LSGM electrolyte. - Electrical conductivity: 570 S.cm -1 around , 170 S.cm -1 at 90 - ASR SmBaCo 2O 5+ (1) SBCO sintered at 1000 : cm 2 at ) (2) composite cathode (SBCO:50, mixture of 50wt% of SBCO and 50wt% of CGO): 0.250, cm 2 at 600 and 700. Thermal properties -TEC ( K -1 ) of SBSCO:50 at ASR (1) cm 2 at 572 GdBaCo 2O 5+ (2) cm 2 at ) (3) cm 2 at 621 (4) cm 2 at 645 -ASR from GBCO/CGO/GBCO (1)0.626.cm 2 at 625 properties -Oxygen surface exchange and oxide ionic diffusivity GdBaCo 2O 5+ (500~700 ) 37) oxygen surface exchange(cm.s -1 ) oxide ionic diffusivity(cm 2.s -1 ) 1.6x x x x x x10-9 properties -Oxygen surface exchange and oxide ionic diffusivity (350 ) PrBaCo 2O 5+ oxygen surface exchange(cm.s -1 ) oxide ionic diffusivity(cm 2.s -1 ) 15) ~x10-3 ~x10-5 Structural changes with respect to the Sr substitution NdBaCo -Tetragonal (x=0 and 0.6) 2O 5+ (NBCO) -ASR from NBCO/CGO/NBCO (1)0.250 cm 2 at 700 tetragonal, Sm, Eu Gd orthorhombic. layered perovskite oxygen content (5+ ) oxygen content A-site Ln. Fig. 3 LnBaCo 2 O 5+ Ln 3+ Ba 2+ c 33) Fig. 4. Schematic crystal structure of LnBaCo2O5+ with, from left to right, (a) =0, (b) =0.5, and (c) =1. 32) ordering. Ln layer. Ln Ln Ba 2+ CO 5 pyramid CO 6 octahedral. 23,24) layered perovskite. 1)A-site ordering : Ln Ba 2)Ln layer 3) CO 5 pyramid CO 6 octahedral. LnBaCo 2 O 5+ Table 2 layered perovskite oxygen contents. 23, 24, 27-29) layered perovskite oxygen content.30) 0 LnBaCo 2 O 5 Fig. 4 (a). Co CO 5 pyramid 1 Fig. 4(c) CO 6 octahedral. 0.5 Fig. 4(b) CO 5 CO 6 Ln-O 27

5 . (001). Co. Co 3+ CO 5 intermediate spin state (t 5 2ge 1 g) CO 6 low spin state (t 6 2ge 0 g) high spin state (t 4 2ge 2 g). spin state oxygen content 5.5 metal insulator transition (MIT) K. 31) 350K metallic SOFC Layered perovskite A / A // B 2 O 5+ layered perovskite LnBaCo 2 O 5+. A / A // B 2 O 5+ A / -site lanthanide A // -site Ba. B-site simple complex perovskite Co Fe IT-SOFC LnBaCo 2 O 5+ type LnBaCo 2 O 5+ Table 3. MIEC Ln lanthanide Pr, Nd, Sm Gd PrBaCo 2 O 5+ (PBCO) 15), NdBaCo 2 O 5+ (NBCO) 33), SmBaCo 2 O 5+ (SBCO) 34) GdBaCo 2 O 5+ (GBCO) 11, 35-37). Fig. 5(a) SBCO 34) 200~ S.cm -1, S.cm Ω.cm 2. Co complex perovskite ( K -1 ). 34) PBCO oxygen surface exchange oxide ionic diffusivity GBCO. 15) 350 PBCO oxygen surface exchange 10-3 (cm.s -1 ) oxide ionic diffusivity 10-5 (cm 2.s -1 ) 15) 300 GBCO oxygen surface exchange( cm.s -1 ) oxide ionic diffusivity ( cm 2.s -1 ). 37) LnBa 1-x Sr x Co 2 O 5+ type LnBa 1-x Sr x Co 2 O 5+ LnBaCo 2 O 5+ layered perovskite A-site Sr layered perovskite. Ln lanthanide Pr, Nd, Sm Gd Sr Table 4. LnBa 1-x Sr x Co 2 O 5+ Sr 0 x 1 IT-SOFC Sr 0.5 mol%. University of St. Andrews Irvine Table 4. LnBa 1-x Sr x Co 2 O 5+ Type Cathode Materials -ASRs from PBSCO/CGO/PBSCO PrBa 0.5Sr 0.5Co 2O 5+ (1)0.689 cm 2 at 600 (PBSCO) (2)0.286 cm 2 at ) (3)0.154 cm 2 at ASRs from SBSCO/CGO/SBSCO (1)0.611 cm 2 at 600 (2)0.244 cm 2 at 650 SmBa 0.5Sr 0.5Co 2O 5+ (3)0.092 cm 2 at ) (SBSCO) -ASR from SBSCO/DLE(CGO coated on 8YSZ)/SBSCO (1)0.196 cm 2 at 600 (2)0.052 cm 2 at 650 (3)0.033 cm 2 at 700 -ASR from SBSCO/CGO/SBSCO GdBa 0.5Sr 0.5Co 2O 5+ (1)1.252 cm 2 at 600 (GBSCO) (2)0.558 cm 2 at ) (3)0.253 cm 2 at 700 Structural changes with respect to the Sr substitution -Tetragonal (x=0 and 0.6) NdBa 0.5Sr 0.5Co 2O 5+ (NBSCO) -ASR from NBSCO/CGO/NBSCO 33) (1)0.11 cm 2 at

6 Ω.cm 2. 38) YSZ CGO Ω.cm 2 YSZ CeO 2 Sr layered perovskite. University of St. Andrews Irvine LnBa 0.5 Sr 0.5 Co 2 O 5+ layered perovskite lanthanide Fig. 5. Electrical conductivities of (a) SmBaCo2O5+ 34) and (b) SmBa0.5Sr0.5Co2O5+ 39) as a function of temperature. Sr 0.5 mol% SmBa 0.5 Sr 0.5 Co 2 O 5+ (SBSCO) 0.5mol%. 38) SBSCO Ce 0.9 Gd 0.1 O 2- (CGO91) (Area Specific Resistance, ASR) Ω.cm Ω.cm 2. SBSCO Fig. 5(b) 50 (1280 S.cm -1 ) 900 (280 S.cm -1 ) Metallic Fig. 5(a) SBCO MIT. 39) YSZ YSZ CGO Ω.cm 2 Pr Nd PrBa 0.5 Sr 0.5 Co 2 O 5+ (PBSCO) NdBa 0.5 Sr 0.5 Co 2 O 5+ (NBSCO) (neutron diffraction). 40) PBSCO NBSCO [Pr- O] [Nd-O] (2a p 2a p 2a p ). layered perovskite (DC 4 probe) 300 metallic (2a p 2a p 2a p ) (a p a p 2a p ). 40) LnBaCo 2 O 5+ -composite type Table 5. LnBaCo 2 O 5+ -composite Type Cathode Materials PrBaCo 2 O 5+ -Composite -ASR from PBCO-composite/CGO/ PBCO-composite 15) (1)0.150 cm 2 at 600 NdBaCo 2 O 5+ -composite -ASR from NBCO:50/CGO/NBCO:50 33) (1)0.061 cm 2 at

7 Table 6. LnBa 1-x Sr x Co 2 O 5+ - composite Type Cathode Materials -ASR from SBSCO:50/ DLE(CGO coated on 8YSZ)/SBSCO:50 SmBa 0.5Sr 0.5Co 2O 5+ (1)0.124 cm2 at ) -Composite (2)0.040 cm 2 at 650 (3)0.019 cm 2 at 700 -ASR from SBSCO:50/CGO/SBSCO:50 (1)0.102 cm 2 at 600 SmBa 0.5Sr 0.5Co 2O 5+ (2)0.038 cm2 at ) -Composite (3)0.016 cm 2 at 700 -Electrical conductivity Maximum (1280 S.cm -1 at 50 ) and minimum (280 S.cm -1 at 900 ) NdBa 0.5Sr 0.5Co 2O 5+ -ASR from NBSCO:50/CGO/NBSCO:50 33) -Composite (1)0.038 cm 2 at 700 Fig. 6. Area specific resistance results for various composite cathodes of CGO91 with SBSCO onto CGO91 electrolyte. 39) The chemical composition of SBSCO:10 indicates the composite cathode comprised of 90 wt% SBSCO and 10 wt% CGO91. In addition, SBSCO:50 displays the composite cathode with 50 wt % SBSCO and 50 wt% CGO91. layered perovskite Table 5. PrBaCo 2 O 5+ (PBCO) CeO 2 composite layered perovskite. 15) PBCO-composite ( ) / CGO ( )/ PBCO-composite ( ) Ω.cm 2 15) NdBaCo 2 O 5+ (NBCO) CGO91 1: Ω.cm 2. 33) LnBa 1-x Sr x Co 2 O 5+ - composite type LnBa 1-x Sr x Co 2 O 5+ Ln Sm Ba Sr 0.5 mol% SmBa 0.5 Sr 0.5 Co 2 O 5+ (SBSCO) CGO91 1:1 SBSCO-composite Ω.cm Ω.cm 2 (Fig.6). 39) NdBa 0.5 Sr 0.5 Co 2 O 5+ (NBSCO) NBSCO-composite Ω.cm 2. 33). Fig. 7. Thermal expansion coefficient results as a function of weight percentages of CGO91 with SBSCO from room temperature to 500, 700, and ) Table 7. LnBaM 2 O 5+ Type Cathode Materials Structural changes with respect to the Ni substitution -Tetragonal (0 x 0.4), Orthorhombic (x=0.6) NdBaCo 2-xNixO 5+ 43) -Power density: maximum power density (560, 350 and 220 mw.cm -2 at 800, 750 and 700 ) Cathode for proton conducting oxide GdBaCoFeO 5+ -Power density: maximum power density 42) (482 mw.cm -2 at 700 ) Thermal properties -TEC ( K -1 ) in the temperature ranges of SmBaCu 2O 5+ -Electrical conductivity: S.cm-1 around at 610 -ASR : 41) (1) cm 2 at 600 (2) cm 2 at 650 (3) cm 2 at

8 Table 6. Fig. 7 SBSCO SOFC K -1. Co layered perovskite. SBSCO-composite K -1 CGO YSZ. 39) LnBa 1-x Sr x Co 2 O 5+. Table 8. LnBa 1-x Sr x M 2 O 5+ Type Cathode Materials Thermal properties -TEC ( K -1 ) of SBSCO and ( K -1 ) of SBSCFO in the temperature ranges of Maximum electrical conductivity: S/cm SmBa 0.5Sr 0.5Cu 2O 5+ -ASR from SBSCO/SDC/SBSCO (SBSCO) and (1) cm 2 at ) SmBa 0.5Sr 0.5CuFeO 5+ (2) cm 2 at 650 (SBSCFO) (3) cm 2 at 700 -ASR from SBSCFO/SDC/SBSCFO (1) cm 2 at 600 (2)1.045 cm 2 at 650 (3) cm 2 at LnBaM 2 O 5+ type Layered perovskite B-site Co Fe Cu Table 7. SmBaCu 2 O 5+ 41) SmBaCo 2 O 5+ ( : K -1 ). Cu S.cm Ω.cm Ω.cm 2. GdBaCoFeO 5+ proton conducting oxide GdBaCoFeO 5+ / BaZr 0.1 Ce 0.7 Y 0.2 O 3- (BZCY7) / Ni- BZCY mw.cm ) Ni. NdBaCo 2-x NixO 5+ Ni Tetragonal(0 x 0.4) Orthorhombic Co Ni oxidation state oxygen content (5+ ). NdBaCo 1.6 Ni 0.4 O 5+ /GDC/LDC/Ni-CGO mw. cm ) LnBa 1-x Sr x M 2 O 5+ type Table 8 SmBa 0.5 Sr 0.5 Co 2 O 5+ Cu SmBa 0.5 Sr 0.5 Cu 2 O 5+ SmBa 0.5 Sr 0.5 Co 2 O 5+ ( K -1 ). 44) Cu Ω.cm Ω.cm 2. 44) B-site Cu Fe SmBa 0.5 Sr 0.5 Cu Fe 2 O 5+ SmBa 0.5 Sr 0.5 Cu 2 O SmBa 0.5 Sr 0.5 Cu 2 O 5+ ( K -1 ). SmBa 0.5 Sr 0.5 CuFe 2 O Ω.cm Ω.cm 2. IT-SOFC layered perovskite. simple perovskite complex perovskite layered perovskite oxygen ion diffusivity surface exchange coefficient. SOFC,,. 31

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