• 한국재료학회지
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• 제11권4호
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• pp.283-289
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• 2001

50/50 vol% LSM-YSZ (La$_{1-x}$Sr$_{x}$MnO$_3$-yttria stabilized zirconia)의 복합공기극이 콜로이드 증착법에 의해 연마된 YSZ 전해질상에 증착되었다. 그 전극 특성은 주사전자현미경, X선회절과 임피던스 분석기에 의해 연구되어졌다. 90$0^{\circ}C$에서 공기/LSM -YSZ/YSZ/Pt/공기 셀에 대해 측정된 전형적인 임피던스 스펙트럼들은 2개의 불완전한 호(depressed arc)로 구성되었다. LSM 전극에 대한 YSZ의 첨가는 전극내의 삼상계(TPB) 영역을 증가시켰으며, 이것이 LSM-YSZ 복합공기극의 비저항을 감소시켰다. 또한 전해질 표면의 불순물 제거와 TPB 길이의 증가를 위한 전해질 표면연마는 공기극의 비저항을 훨씬 더 감소시켰다. LSM-YSZ 공기극의 비저항은 작동온도, 공기극의 조성과 입자크기, 인가전류 및 전해질의 표면거칠기에 의해 큰 영향을 받았다.

• 한국세라믹학회지
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• 제56권5호
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• pp.497-505
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• 2019

Lanthanum-based transition metal cations containing perovskites have emerged as potential catalysts for the intermediate-temperature (600-800℃) oxygen reduction reaction (ORR). Here, we report a facile acetylacetone-assisted combustion route for the synthesis of nanostructured La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The as-prepared powder was analyzed by thermogravimetry analysis-differential scanning calorimetry. The powder calcined at 800℃ was characterized by X-ray diffraction, scanning electrode microscopy, energy dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller surface area measurements. It was found that the porosity of the air electrode significantly increased by utilizing the nanostructured LSCF6428 instead of commercial powder. The performance of a single cell fabricated with the nanostructured LSCF6428 cathode increased by 112%, from 0.4 to 0.85 W cm^-2, at 700℃. Electrochemical impedance spectroscopy showed a considerable reduction in the area-specific resistance and activation energy from 133.5 to 61.5 kJ/mol, resulting in enhanced electrocatalytic activity toward ORR and overall cell performance.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.30-31
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• 2006

The LSCF cathode for Solid Oxide Fuel Cell was investigated to develop high performance unit cell at intermediate temperature by modified oxalate method with different electrolyte. The LSCF precursors using oxalic acid, ethanol and $NH_4OH$ solution were prepared at $80^{\circ}C$, and pH was controlled as 2, 6, 7, 8, 9 and 10. The synthesis precursor powders were calcined at $800^{\circ}C$, $1000^{\circ}C$ and $1200^{\circ}C$ for 4hrs. Unit cells were prepared with the calcined LSCF cathode, buffer layer between cathode and each electrolyte that is the LSGM, YSZ, ScSZ and CeSZ. The synthesis LSCF powders by modified oxalate method were measured by scanning electron microscope and X-ray diffraction. The interfacial polarization resistance of cell was characterized by Solatron 1260 analyzer. The crystal of LSCF powders show single phase at pH 2, 6, 7, 8 and 9, and the average particle size was about $3{\mu}m$. The electric conductivity of synthesis LSCF cathode which was calcined at $1200^{\circ}C$ shows the highest value at pH 7. The cell consist of GDC had the lowest interfacial resistance (about 950 S/cm@650) of the cathode electrode. The polarization resistance of synthesis LSCF cathode by modified oxalate method has the value from 4.02 to 7.46ohm at $650^{\circ}C$. GDC among the electrolytes, shows the lowest polarization resistance.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.305-305
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• 2007

SOFC용 밀봉유리$({\sim}10.0{\times}10^{-7}/K)$의 열팽창 계수를 SUS430$({\sim}12.0{\times}10^{-7}/K)$ 인터커넥터에 매칭 시키기 위하여 모유리에 비하여 열팽창계수가 큰 $CaTiO_3\;({\sim}13.5{\times}10^{-7}/K)$ 입자를 필러로서 첨가하였다. 필러입자의 첨가량이 증가함에 따라 밀봉재의 열팽창 계수가 증가하고, 동일 함량의 필러를 첨가하는 경우 필러 입자의 크기가 작을 수록 밀봉재의 연화점 상승 폭이 커서 SUS430 기판과의 접합 상태가 불량해짐을 관찰하였다. 필 테스트, 접합시험, 미세구조 분석 등을 통하여 필러 입자 크기가 증가 할 수록 SUS430과의 접합이 가능한 범위 내에서 보다 많은 양의 필러를 첨가하는 것이 가능하기 때문에 열팽창 계수 제어가 용이하다는 것을 확인 할 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제19권6호
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• pp.661-666
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• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.

• 대한금속재료학회지
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• 제50권9호
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• pp.685-690
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• 2012

Decalcomania is a new method for SOFCs (solid oxide fuel cells) unit cell fabrication. A tight and dense $5{\mu}m$ Yttria-stabilized zirconia (8YSZ) electrolyte layer on anode substrate was fabricated by the decalcomania method. After 8YSZ as the electrolyte starting material was calcined at $1200^{\circ}C$, the particle size was controlled by the attrition mill. The median particle size (D50) of each 8YSZ was $39.6{\mu}m$, $9.30{\mu}m$, $6.35{\mu}m$, and $3.16{\mu}m$, respectively. The anode substrate was coated with decalcomania papers which were made by using 8YSZ with different median particle sizes. In order to investigate the effect of median particle sizes and sintering conditions on the electrolyte density, each sample was sintered for 2, 5 and 10 h, respectively. 8YSZ with a median particle size of $3.16{\mu}m$ which was sintered at $1400^{\circ}C$ for 10 had the highest density. With this 8YSZ, a SOFCs unit cell was manufactured with a $5{\mu}m$ layer by the decalcomania method. Then the unit cell was run at $800^{\circ}C$. The Open Circuit Voltage (OCV) and Maximum power density (MPD) was 1.12 V and $650mW/cm^2$, respectively.

• 전기화학회지
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• 제4권2호
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• pp.58-64
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• 2001

기체/전해질/LSM $(La_{0.85}Sr_{0.15}MnO_3)$ 공기극이 만나는 삼상계면 (triple phase boundary) 주위에 YSZ ($8mol\%$ yttria stabilized zirconia) 코팅막 (coating film) 을 형성하여 추가로 삼상계면을 크게 늘린 새로운 전극 미세구조를 갖는 복합 공기극 (composite cathode) 을 개발하였다. 이 복합 공기극을 전해질 두께가 약 $30{\mu}m$인 연료극 (anode)v 지지체 위에 형성하여 $700\~800{\circ}C$의 온도에서 전류전압 특성 및 교류 임피던스 분석을 실시하였다. $800^{\circ}$, 공기 및 수소 조건에서 교류 임피던스 분석 결과 1000Hz주파수 영역을 대변하는 저항성분 R1은 연료극 분극 저항에 해당하였고 100Hz주파수 영역의 저항성분 R2는 공기극 분극 저항 성분, 그리고 10Hz이하 영역의 저항성분 R3는 전극을 통한 기체확산 저항성분으로 특히, 작동 조건인 공기 및 수소 분위기에서는 연료극 쪽 반응기체에 의한 기체확산 저항 성분임을 알 수 있었다. 전지성능 측정 결과 이 복합 공기극을 장착한 전지는 $800^{\circ}C$, 공기 및 산소 조건에서 각각 $0.55W/cm^2$ $1W/cm^2$의 높은 전지성능을 나타내었다. 전류전압 곡선은 기울기가 다른 두 구간으로 구분되었으며, 낮은 전류밀도 하에서 보이는 급격한 전압감소 구간은 공기극 분극저항이 주된 성능 저하의 원인인 반면, 높은 전류밀도 하에서 나타나는 완만한 전압 감소 구간은 전해질에 관련된 분극저항이 주된 성능 저하의 원인이었다.

• 세라미스트
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• 제21권4호
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• pp.378-387
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• 2018

The optimal fabrication conditions for $Gd_{0.1}Ce_{0.9}O_{2-{\delta}}$(GDC) buffer layer and $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ (LSCF) cathode on 1mol% $CeO_2-10mol%\;Sc_2O_3$ stabilized $ZrO_2$ (CeScSZ) electrolyte were investigated for application of IT-SOFCs. GDC buffer layer was used in order to prevent undesired chemical reactions between LSCF and CeScSZ. These experiments were carried out with $5{\times}5cm^2$ anode supported unit cells to investigate the tendencies of electrochemical performance, Microstructure development and interface reaction between LSCF/GDC/CeScSZ along with the variations of GDC buffer layer thickness, sintering temperatures of GDC and LSCF were checked, respectively. Electrochemical performance was analyzed by DC current-voltage measurement and AC impedance spectroscopy. Microstructure and interface reaction were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Although the interfacial reaction between these materials could not be perfectly inhibited, We found that the cell, in which $6{\mu}m$ GDC interlayer sintered at $1200^{\circ}C$ and LSCF sintered at $1000^{\circ}C$ were applied, showed good interfacial adhesions and effective suppression of Sr, thereby resulting in fairly good performance with power density of $0.71W/cm^2$ at $800^{\circ}C$ and 0.7V.

• 한국결정성장학회지
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• 제29권5호
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• pp.187-191
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• 2019

고체전지, 산화물연료전지, 센서, 산화물 분리막 등 에너지 재료로 활용이 무궁한 산소 이온 전도체 중 acceptor가 첨가된 $LaAlO_3$의 전기적 특성과 고온에서의 혼합전도체로 사용 가능성을 연구하였다. Sr과 Mg을 $LaAlO_3$에 동시에 첨가하여 만든 LSAM의 전기적 특성을 교류(a.c.)와 직류(d.c.) 방법을 이용하여 다양한 산소 분압에서 측정하였다. 교류 임피던스 방법을 이용하여 LSAM의 전체 저항에서 입자(grain) 저항과 입계(grain boundary) 저항을 분리한 결과, $550^{\circ}C$ 이하의 온도에서는 입계 저항이 지배적이나 $800^{\circ}C$ 이상의 온도에서는 입자 저항이 대부분임을 알 수 있었다. 또 산소분압에 따른 전도도 측정을 물질의 결함모델(defect model)을 이용하여 분석해 전체 전도도를 이온 전도도와 전자 전도도로 분리하였다. 그 결과, $800^{\circ}C$ 이상의 고온에서 LSAM은 낮은 산소분압($Po_2$ < $10^{-10}atm$)에서는 산소이온 전도체이고 높은 산소분압($Po_2$ > $10^{-5}atm$)에서는 혼합전도체의 거동을 보였다. 또 온도가 증가하여도 산소이온 전도가 주도적인 산소분압의 영역은 줄어들지 않았고 낮은 산소분압에서도 안정적인 전기적 특성을 보이는 등으로 보아, LSAM은 고온의 낮은 산소분압(T > $1500^{\circ}C$, $Po_2$ < $10^{-10}atm$) 조건에서 용강에서의 산소이온센서와 같은 산소이온체로의 사용 가능성이 높다.