• Journal of the Korean Electrochemical Society
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• v.11 no.2
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• pp.89-94
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• 2008

We synthesized and investigated $(La_{0.75}Sr_{0.25})_{1-x}FeO_{3-\delta}$ perovskite oxides having different stoichiomety (x = 0, 0.02, 0.04, 0.06, 0.08) as cathode materials. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The electrochemical performances of the synthesized powders were investigated by AC impedance spectroscopy. Both the electric conductivity and the electrochemical performance showed the highest properties at the stoichiometry x = 0.02. Finally, we concluded that the variation of A-site deficiency results in the variation of the amount of oxygen vacancy and micro structure, which leads to the variation of electric conductivity and polarization resistance.

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.251-259
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• 2005

In order to characterize the influence of the reaction-site density on the cathodic polarization property of LSCF, we chose the porosity of LSCF as a main controlling variable, which is supposed to be closely related with active sites for the cathode reaction. To control the porosity of cathodes, we changed the mixing ratio of fine and coarse LSCF powders. The porosity and pore perimeter of cathodes were quantitatively analyzed by image analysis. The electrochemical half cell test for the cathodic polarization was performed via 3-probe AC-impedance spectroscopy. According to the investigation, the reduction of oxygen at LSCF cathode was mainly controlled by following two rate determining steps; i) surface diffusion and/or ionic conduction of ionized oxygen through bulk LSCF phase, ii) charge transfer of oxygen ion at cathode/electrolyte interface. Moreover, the overall cathode polarization was diminished as the cathode porosity increased due to the increase of the active reaction sites in cathode layer.

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.269-275
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• 2005

We analyzed the unit cell performance against the cathode porosity, which is supposed to be closely related with active sites for the cathode reaction. In order to fabricate the unit cells with different porosity in the cathode layer we changed the mixing ratio of fine and coarse LSCF cathode powders. The final porosity of each cathode layer was 14, 23, 27, $39\%$ respectively. According to the electrochemical analysis of unit cell performance via DC current interruption and AC impedance method, the electrodic polarization resistance was diminished as the cathode porosity increased. The decrease of polarization resistance was attributed due to the increase of active reaction sites and the enhancement of overall unit cell performance could be explained in the same line.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.196-199
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• 2007

The chemical states of oxygen on the surfaces of $Pr_{1-x}Sr_{x}CoO_{3}$ (x=0.5 and 0.7) oxide systems were investigated by X-ray photoelectron spectroscopy. Merged oxygen peaks of $Pr_{1-x}Sr_{x}CoO_{3}$ (x=0.5 and 0.7) oxides could be divided as five sub-peaks. These five sub-peaks could be defined as lattice oxygen ($O_{L}$). chemisorbed oxygen peaks ($O_{C}$) and hydroxyl condition oxygen peak ($O_{H}$). In case of the $Pr_{0.5}Sr_{0.5}CoO_{3}$ and $Pr_{0.3}Sr_{0.7}CoO_{3}$, the binding energy (BE) of oxygen lattice were located at same BE. However, the BE of chemisorbed oxygen peaks including oxygen vacancy shows different BE. Especially, it was found that BE of chemisorbed oxygen peaks was increased when more Sr were substituted. Comparing atomic percentages of oxygens of $Pr_{0.5}Sr_{0.5}CoO_{3}$ and $Pr_{0.3}Sr_{0.7}CoO_{3}$, the ratio of $Pr_{0.3}Sr_{0.7}CoO_{3}$ was higher than that of $Pr_{0.5}Sr_{0.5}CoO_{3}$. It showed more chemically adsorbed site including oxygen vacancies were existed in $Pr_{0.3}Sr_{0.7}CoO_{3}$.

• Applied Chemistry for Engineering
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• v.16 no.1
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• pp.45-51
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• 2005

$K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$ in the $K_2O-Li_2O-Al_2O_3$ ternary system was synthesized using aluminum nitrate solution as a starting material. For the synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$, raw materials with chemical composition of $0.84K_2O{\cdot}0.082Li_2O{\cdot}5.2Al_2O_3$ were mixed in solution state. The effects of dispersant and solution-pH were investigated in minimizing the particle size and on the synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$. Ethanol was used for a dispersant, and $NH_4OH$ solution and nitric acid were added for pH adjustment. The solution pH was increased from 1.0 to 7.5 by 0.5 increments. Each sample was calcined at $1200^{\circ}C$ for 2 h and characterized with X-ray diffraction and particle size analyzer. The pH of solution significantly effected both particle size and phase formation, while the addition of ethanol only effected particle size. The synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$ was favored by addition of nitric acid (for pH control).

• Journal of Hydrogen and New Energy
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• v.22 no.2
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• pp.161-167
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• 2011

Proton conductors have attracted considerable attention for solid oxide fuel cell (SOFC), hydrogen pump, gas sensor, and membrane separators. Doped $SrCeO_3$ exhibits appreciable proton conductivity in hydrogen-containing atmosphere at high temperature. However commercial realization has been hampered due to the reactivity of $SrCeO_3$ with $CO_2$. The chemical stability and proton conductivity are dependent on dopant type. The purpose of this work is to investigate chemical stability of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composites in $CO_2$ and $H_2$ gases. Thermogravimetric analysis (TGA) was performed in gaseous $CO_2$ and electrical conductivity of the composites were also measured between 500 and $900^{\circ}C$ in air and $H_2$ atmosphere. $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composite membranes showed good chemical stability of in $CO_2$ atmosphere and high conductivity at hydrogen condition. The hydrogen permeation of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composite membranes was investigated as a function of volumetric content of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}$. The $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$(6:4) membrane with a thickness of 1.0 mm showed the highest hydrogen permeability with the flux reaching of 0.12 $ml/min{\cdot}cm^2$ at $800^{\circ}C$ in 100%$H_2/N_2$ as feed gas.

• Journal of Energy Engineering
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• v.25 no.4
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• pp.251-258
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• 2016

This article reports current status of micro fuel cell-combined heat and power (${\mu}FC$-CHP) systems which utilize both power and heat generated by fuel cells. There are several options for constructing CHP systems and among them, fuel cells are the most useful and their total energy efficiency combining heat and power can reach up to about 90%. Fuel cells are classified as five types based on the electrolyte, but the most suitable fuel cell types for the ${\mu}FC$-CHP system are proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs). ${\mu}FC$-CHP systems have several advantages such as decrease of the transmission-distribution loss, reduced costs of electricity due to distributed power generation, and environmental-friendliness owing to zero emission. The main drawback of the ${\mu}FC$-CHP systems is the high initial investment, however, it keeps decreasing as the technology development reduces production costs. Currently, Japan is the most leading country of the ${\mu}FC$-CHP market, however, Korea tries to expand the market by planning the deployment of 1 million units of ${\mu}FC$-CHP systems and governmental subsidiary supporting of half of the install price. In this report, integration technologies for connecting FC and CHP, and technology trends of leading countries are presented as well.

• Journal of the Korean Ceramic Society
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• v.49 no.2
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• pp.197-203
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• 2012

In this study, in order to improve densification of $La_{0.8}Ca_{0.2}Cr_{0.9}Co_{0.1}O_{3-\delta}$ (LCCC), which is known for one of the most proper candidate interconnector materials in the solid oxide fuel cells, $CaCrO_4$ was prepared via solid oxide synthesis route and added to the LCCC with different amount and particle sizes. As the amount of the $CaCrO_4$ increased, porosity of the sintered samples increased, and the pore size was proportional to the particle size of the $CaCrO_4$. This supports the fact that the $CaCrO_4$ phase forms liquid during sintering and permeate into the matrix leaving behind large pores. Then the liquid reacts with the matrix through the solid solution. However, when the samples were sintered with a slow ramp up rates, the porosity decreased. This is thought to be caused by the progressive solid solution of $CaCrO_4$ before the temperature reach to the melting temperature and forms a fluent amount of liquids. The sintering behavior of the LCCC with the addition of $CaCrO_4$ was analyzed through the transient liquid phase sintering on the basis of the microstructure observation and phase identification by x-ray diffraction.

• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.853-859
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• 2001

The dispersion stability of nano $Y_2O_3-CeO_2$ system was investigated using colloid surface chemistry. Green body of $Y_2O_3$ doped $CeO_2$ was prepared by slip casting in and aqueous system. The dispersion stability of suspension between powders and organic additive was accomplished through electrokinetic behavior of suspension, which was done by ESA apparatus. The dynamic mobility of particles was enhanced when the anionic dispersant of the amount of 1wt% was added. The dissolution of $Y^{3+}$ ion in suspension occurred in the acidic region so that pH value in slurries did not move to below 7.0. In the $CeO_2-Y_2O_3$ system, optimal preparation of suspension was made after adding the anionic dispersant as the amount of 1wt% and pH value of 11.0, and then slip-cast and sintered at 1400$^{\circ}$C, 2 hrs. It appeared relative density of >98% and homogeneous distribution of Y element in depth direction as well as in the microstructure of surface.

• Journal of the Korean Electrochemical Society
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• v.10 no.1
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• pp.7-13
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• 2007

We synthesized and investigated $La_{0.75}Sr_{0.25}FeO_3$ by Glycine Nitrate Process(GNP) method used as cathode materials for SOFC(solid oxide fuel cell). Optimized amount of glycine is 3.17 mol. ICP elemental composition analysis indicated that the stoichiometry of the synthesized powders have nearly nominal values. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The sample powders were isostatically pressed to form a pellet. The green body was sintered at $1200^{\circ}C$ and the relative density of the sintered specimens were measured by Archimedes mettled. We measured electrochemical performance of LSF by AC impedance spectroscopy. Resistance of LSF shows lower value than that of LSM throughout all temperature region. The anode-supported solid oxide fuel cell showed a performance of $342mW/cm^2(0.7V,\;488mA/cm^2)$ at $750^{\circ}C$. The electrochemical characteristics of the single cell were examined by at impedance method.