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1 Jurnal f the Krean Ceramic Sciety Vl. 44, N. 12, pp. 710~714, Effect f the LDC Buffer Layer in LSGM-based Ande-supprted SOFCs Eun Hwa Sng* S **, Tai-J Chung**, Hae-Ryung Kim*, Ji-Wn Sn*, Byung Kk Kim*, Jng-H Lee*, and Hae-Wen Lee* *Materials Science & Technlgy Research Divisin, Krea Institute f Science and Technlgy, Seul , Krea **Schl f Materials Science & Engineering, Andng Natinal University, Andng , Krea (Received Nvember 7, 2007; Accepted Nvember 56, 2007) LSGM x š y LDC d z y*, **Á k **Á½x * Á *Á½ *Á y*á w * *w w»» ** w œw ( ; ) ABSTRACT LSGM(La 0.8 O 3-δ) is the very prmising electrlyte material fr lwer-temperature peratin f SOFCs, especially when realized in ande-supprted cells. But it is ntrius fr reacting with ther cell cmpnents and resulting in the highly resistive reactin phases detrimental t cell perfrmance. LDC(La 0.4 ), which is knwn t keep the interfacial stability between LSGM electrlyte and ande, was adpted in the ande-supprted cell, and its effect n the interfacial reactivity and electrchemical perfrmance f the cell was investigated. N severe interfacial reactin and crrespnding resistive secndary phase was fund in the cell with LDC buffer layer, and this is due t its ability t sustain the La chemical ptential in LSGM. The cell exhibited the pen circuit vltage f 0.64 V, the maximum pwer density f 223 mw/cm 2, and the hmic resistance f 0.17 Ωcm 2 at 700 C. These values were much imprved cmpared with thse frm the cell withut any buffer layer, which implies that frmatin f the resistive reactin phases in LSGM and then deteriratin f the cell perfrmance is resulted mainly frm the La diffusin frm LSGM electrlyte t ande. KeyG wrds : SOFC, LSGM electrlyte, Buffer layer, Interfacial reactin, Cell perfrmance 1. š y (slid xide fuel cell; SOFC) xk yz š p w w j» l w, w ƒÿ š. û š (500 ~ 800 C) SOFC w y w š, w w y 6-7) w. 1-3) š y w» w 1,4), w, w w., (10 18 P O2 /atm 1) ù (inic transference number)ƒ 1 w., ƒ Crrespnding authr : Hae-Ryung Kim hrkim@kist.re.kr Tel : Fax : f w w yw w., š» w., wš, q w w w w w. e w(dense) x w yw ù w w. w l x š w š g (ZrO 2 )ù (CeO 2 ) x (flurite) y LaGaO 3 r e p(pervskite) y. g y ƒ š yw /» w YSZ(Y 2 O 3 -stabilized ZrO 2 )ƒ t, YSZ 1000 C ƒ 0.1 S/cm ƒ 800 C 0.04 S/cm w û p e. 5) y 800 C w g ƒ ù, y» ƒ f e w 710

2 LSGM x š y LDC d z 711 x w. r e p 9) LaGaO 3 (La 0.8 O 3-δ; LSGM) y 800 C w e w ƒ, w w ƒ. w 10) LSGM w yw w ƒ. ù g w 11-15) LaSrGa 3, LaSrGaO 4, La 2 Zr 2, Sr 2 ZrO 4» ƒ û j j š. 11,14,15) NiO LaNiO 3 LSGM r e p w w e š. y w 8) w x x wù, x w / œ ƒ w e. LSGM x w / w d š w š, d w CeO 2 La š LDC(La 2 O 3 -dped CeO 2 ) w. LDC d LSGM w e w k, p z w š w. 2. x LSGM w d LDC(La 0.4 ) š (slid state reactin) w. La 2 O 3 ( 99.99%, by Strem Chemicals, USA) CeO 2 ( 99.99%, by Strem Chemicals, USA) w. La 2 O 3 CeO 2 yw 40 : 60 vl% y d wš g wì 24 ball-millingw z, yww wš, w ³ w, 1350 C 5 w w. w w /»(thermgravimetry/differential thermal analysis; TG/DTA, STA409PC by Netzsch, Germany) d š x14,16) ü k w w. w X- z»(x-ray diffractin; XRD, D/max2000 by Rigaku, Japan) w w ww, d 40 kv, 30 ma, 4 /min scanning speed. x (ande-supprted unit cell) w GDC(Gd 0.1 Ce 0.9 O 1.95, by Rhdia, USA) NiO(by Sumitm, Japan) 40 : 60 vl% yww z, (liquid cncentratin prcess; LCP) mw ³ w j» NiO-GDC w. 10 MP ƒ xw z 1100 C 2 ƒ w 1mm Ì»q w. w w. LSGM(La 0.8 O 3-δ, by Seimi Chemical, Japan) w LSCF(La 0.6 Sr 0.4 C 0.8 Fe 0.2 O 3-δ, by Seimi Chemical, Japan) LDC(La 0.4 ) d Planetary Milling(Pulverisette5 by Fritsch, Germany) w r p w š, w j d z w. LDC d 1400 C 5, LSGM w 1400 C 6, LSCF 1100 C 2 w. y w» w x (scanning electrn micrscpy; SEM, XL-30 by Philips/ FEI, Netherlands) (secndary electrn; SE) z (back-scattered electrn; BSE) w š, ƒ y» w x» (energy dispersive spectrscpy; EDS) / (line/pint mapping) ww.»yw d e w šw. 21) w ƒƒ Pt mesh Ni spnge w Pt w»» w. ƒ 200 sccm, yƒ 400 sccm œ» w, ƒ yƒ yw» w w ƒ fx w. 600 ~ 700 C 50 C - š v rp d w (1260A & 1287A by Slartrn Analytical, England) p w. 3. š 3.1. LDC w d ƒ y / yw w, w w. LDC» ƒ, La 40% LSGM w ü La yw sl g w La y w š š. 16) š w LDC w w z, sƒ mw w y w. Fig. 1 LDC TG/DTA, 300 ~ 800 C w ƒ, y s ùkû. Y y (%) / w ƒ 100» 44«12y(2007)

3 712 yá k Á½x Á Á½ Á yá w w ƒ. w 1300 C w y w. sƒ š x14,16) ü k LDC w 1350 C w. Fig C 5 w w LDC X- z, k 1350 Cƒ (cubic) x w ww LDC d e z LDC d e w wš, Fig. 3 d EDS ùkü. d, w d (Fig. 3(a)). Fig. 3(b) EDS, w La, Ni w w w š, w y x d x w. Fig. 3(c) EDS mw, d w ƒ¾ z d (A) La, Sr, Ga, O LaSrGa 3, ƒ¾ d(b) Ni, O NiO y w. Ni LSGM w LaNiO 3 ƒ j, mw w. Fig. 4 LDC d w w EDS. w / w š(fig. 4(a)), Ni, O y. LDC d y y wš, EDS / ww (Fig. 4(b-c)). LDC d ü La yw sl w w La š, LSGM/LDC La y La, Sr, Ga, O w ƒ d. LDC/ LDC d La ƒ y w, LDC w» d. ù w ü Ni, LDC d w w Ni y y w., w / y, p w La ùƒ w j La-Sr-Ga-O d x w e. La š LDC d w w w y w š, w w w. ù w Ni LDC d w w LDC d»yw e z»yw - š l z (pen circuit vltage; OCV) (maximum pwer density), v rp l w w d w sƒw. Fig. 5 LDC d w w d. 700 C OCV 0.64 V, 223 mw/cm C OCV 0.65 V 174 mw/cm 2, 600 C ƒƒ 0.66 V mw/cm d. Fig. 6 w v rp. ƒ w rp, š q r w ù kü, l q r¾ ¼ ƒ w w w. w w j» w v d z (effective area) š w w (area specific resistance; ASR) w. 700 C ASR 0.17 Ω cm 2 š, 650 C 600 C ASR ƒƒ 0.26 Ω 2 cm 0.46 Ω cm 2 d. w š x9,16-20) š, LDC d x w û r, w z w w. Fig C LDC d d w v. sƒw 0.7 V w, OCV j k 700 C w. d C OCV 0.42 V š, 0.40 mw/cm û. w û OCV d k LSGM w w w j La-Sr-Ga-O w q. LDC d 700 C OCV 0.64 V, 223 mw/cm 2 d, d w , LDC d LSGM La š g w w š» w» š. LDC d w Ni», Ni y w La y w d x w e w wz

4 LSGM x š y LDC d z 713. LDC d w La y w š š w. Fig. 8 LDC d ƒƒ w 700 C v mw ASR w. d ASR Ω cm 2, LDC d 0.17 Ω cm 2 d. y w l, La y La-Sr-Ga-O d w w ƒ w. LDC d ASR š 5/10/10 µm LDC/LSGM/LDC d ƒ x ASR 16) w (Fig. 9). š x ASR 10 µm LSGM ƒ x ASR 17) w 3 j, LDC/LSGM/LDC d ̃ 25 µm w k w. LSGM w LDC d ̃ ƒƒ 20 µm, Ì ASR 10 µm LSGM» ASR 4 j ù, 10. w ƒ š w. Fig. 10 w w ü ³, LSGM w LSCF q w ü (interfacial thermal stress) w, 20) mw. w La y w Ni y w j w w, OCV ù w ƒ w w w ƒ v w. l, LSGM x w d w w, LDC d w w ü La š g w j d w ü w ywš w w y w. wr y w / w, w Ni y ƒ w w. 4. LSGM w w x SOFC w w w» w LDC d w, w ƒw. SEM EDS LSGM La y w x, ü w ƒ wƒ. LDC d w LSGM w ü La yw sl w w y w. ù y w / w, w Ni y ƒ w w. Acknwledgment ƒ y w. REFERENCES 1. N. Q. Minh and T. Takahashi, Science and Technlgy f Ceramic Full Cells, pp , Elsevier, Amsterdam, N.Q. Minh, Ceramic Fuel Cells, J. Am. Ceram. Sc., 76 [3] (1993). 3. T. Ishihara, N. M. Sammes, and O. Yamamt, Electrlytes, pp , in <High Temperature Slid Oxide Fuel Cell: Fundamentals, Design and Applicatins>, Ed. by S.C. Singhal and K. Kendall, Elsevier, New Yrk, B.C.H. Steele, Ceramic In Cnducting Membranes, Current Opinin in Slid State & Materials Science, 1 [5] (1996). 5. Y. Arachi, H. Sakai, O. Yamamt, Y. Takeda, and N. Imanishai, Electrical Cnductivity f the ZrO 2 -Ln 2 O 3 System, Slid State Inics, 121 [1-4] (1999). 6. T. Fukui, S. Ohara, K. Murata, H. Yshida, K. Miura, and T. Inagaki, Perfrmance f Intermediate Temperature Slid Oxide Fuel Cells with La(Sr)Ga(Mg)O 3 Electrlyte Film, J. Pwer Surces, 106 [1-2] (2002). 7. N.P. Brandn, S. Skinner, and B.C.H. Steele, Recent Advances in Materials fr Fuel Cells, Annu. Rev. Mater. Res., (2003). 8. P.Huang, A. Hrky, and A. Petric, Interfacial Reactin between Nickel Oxide and Lanthanum Gallate during Sintering and Its Effect n Cnductivity, J. Am. Ceram. Sc., 82 [9] (1999). 9. Z.H. Bi, B.L. Yi, Z.W. Wang, Y.L. Dng, H.J. Wu, Y.C. She, and M.J. Cheng, A High-perfrmance Ande-supprted SOFC with LDC-LSGM Bilayer Electrlytes, Electrchem. Slid St., 7 [5] A (2004). 10. T. Ishihara, H. Matsuda, and Y. Takita, Dped LaGaO 3 Pervskite Type Oxide as a New Oxide Inic Cnductr, J. Am. Chem. Sc., 116 [9] (1994). 11. M. Hrvat, A. Ahmad-Khanln, Z. Samardzija, and J. Hlc, 44«12y(2007)

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