• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.229-234
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• 2004

In this study, we proposed new forming process for a porous ceramic body with unique pore structure. h tubular-type porous NiO-YSZ body with radially aligned pore channels was prepared by freeze-drying of aqueous slurry. A NiO-YSZ slurry was poured into the mold, which was designed to control the crystallization direction of the ice, followed by freezing. Thereafter the ice was sublimated at a reduced pressure. SEM observations revealed that the NiO-YSZ porous body showed aligned large pore channels parallel to the ice growth direction, and fine pores are formed around the outer surface of the tube. It was considered that the difference in the ice growth rate during the freezing process resulted in such a characteristic microstructure. Bilayer consisting of dense thin electrolyte film of YSZ onto the tubular type porous body has been successfully fabricated using a slurry-coating process followed by co-firing. It was regarded that the obtained bilayer structure is suitable for constructing electrode-support type electrochemical devices such as solid oxide fuel cells.

• Korean Journal of Materials Research
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• v.11 no.4
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• pp.283-289
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• 2001

Composite cathodes of 50/50 vol% LSM- YSZ (La$_{1-x}$Sr$_{x}$MnO$_3$-yttria stabilized zirconia) were deposited onto surface- Polished YSZ electrolytes by colloidal deposition technique. The cathode characteristics were then examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and studied by ac impedance spectroscopy (IS). The typical impedance spectra measured for an air/LSM- YSZ/YSZ/Pt/air cell at $700^{\circ}C$ were composed of two depressed arcs. Addition of YSZ to the LSM electrode significantly enlarged the triple-phase boundaries (TPB) length inside the electrode, which led to a pronounced decrease in cathodic resistivity of LSM-YSZ composite electrodes. Polishing the electrolyte surface to eliminate the influences of surface impurities and to enlarge the TPB length can further reduce cathode resistivity. The cathodic resistivity of the LSM- YSZ electrodes was a strong function of operation temperature, composition and particle size of cathode materials, applied current, and electrolyte surface roughness.

• Journal of the Korean Ceramic Society
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• v.56 no.5
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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.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.5
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• pp.609-615
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• 2011

A 5 kW class SOFC system for cogeneration power units was consisted of a hot box part and cold BOPs. High temperature components such as a stack, a fuel reformer, a catalytic combustor, and heat exchanges are arranged in the bot box considering their operating temperatures for the system efficiency. The hot box was made of ceramic boards for the thermal insulation. A 5 kW class SOFC stack was composed of 2 sub-modules and each module had 64 cells with $15{\times}15cm^2$ area and stainless steel interconnects. The 5 kW class SOFC system was operated with a hydrogen and a city gas. With a hydrogen, the total power of the stacks was about 7.1 kWDC and electrical efficiency was about 49.3% at 80 A. With a city gas, the total power of the stacks was about 5.7 $kW_{DC}$ and electrical efficiency was about 38.8% at 60 A. Under self-sustained operating condition, the system efficiency including a power conditioning loss and a consumed power by BOPs was about 30.2%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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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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• v.19 no.6
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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.

• Korean Journal of Metals and Materials
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• v.50 no.9
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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.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.6
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• pp.707-714
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• 2022

Hydrogen production using solid oxide electrolysis cells (SOEC) is a promising technology because of its efficiency, cleanness, and scalability. Especially, high-power SOEC system has received a lot of attention from researchers. This study compared and analyzed the low-power and high-power SOEC system in term of economic. By using revenue requirement method, levelized cost of hydrogen (LCOH) was calculated for comparison. In addition, the sensitivity analysis was performed to determine the dependence of hydrogen cost on input variables. The results indicated that high-power SOEC system is superior to a low-power SOEC system. In the capital cost, the stack cost is dominant in both systems, but the electricity cost is the most contributed factor to the hydrogen cost. If the high-power SOEC system combines with a nuclear power plant, the hydrogen cost can reach 3.65 $/kg when the electricity cost is 3.28 ¢/kWh and the stack cost is assumed to be 574 $/kW.

• Journal of the Korean Society of Food Science and Nutrition
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• v.44 no.4
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• pp.516-523
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• 2015

This study investigated the antimutagenic and anticancer effects of Platycodon grandiflorum extract (PGE) and its fractions against carcinogenic N-nitrosodimethylamine (NDMA) and genotoxicity. The Ames Salmonella mutagenicity test employing histidine mutants of Salmonella Typhimurium TA98 and TA100 was used to examine the mutagenicity of PGE and its fractions. Bacterial reversion assay with S. Typhimurium TA98 and TA100 did not show a significantly increased number of revertant colonies. The same test was used to examine the ability of PGE and its fractions to prevent acquisition of N-methyl-N'-nitro-N-nitrosoguanidine- and 4-introquino-line-1-oxide-induced mutations. PGE and its fractions inhibited mutagenesis in a dose-dependent manner. Among the fractions, ethyl acetate fraction from PGE (PGEA) exhibited a higher antimutagenic effect than other fractions. PGE and its fractions suppressed the growth of cancer cell lines, including human cervical adenocarcinoma, human hepatocellular carcinoma, human breast adenocarcinoma, human lung carcinoma, and transformed primary human embryonic kidney cells. In addition, we evaluated the antitumor activity of PGEA and its fractions in sacorma-180 solid tumor-bearing mice. In vivo anticancer activity results showed that PGE and its fractions could more effectively suppress tumor growth than the control. PGEA showed higher in vitro and in vivo anticancer effects than PGE and other fractions, and PGEA inhibited NDMA formation. Thus, we showed that PGEA has antimutagenic and anticancer activities, making it a candidate anticancer material under these experimental conditions.