• 한국분말재료학회지
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• 제21권3호
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• pp.222-228
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• 2014

Much research into fuel cells operating at a temperature below $800^{\circ}C$. is being performed. There are significant efforts to replace the yttria-stabilized zirconia electrolyte with a doped ceria electrolyte that has high ionic conductivity even at a lower temperature. Even if the doped ceria electrolyte has high ionic conductivity, it also shows high electronic conductivity in a reducing environment, therefore, when used as a solid electrolyte of a fuel cell, the powergeneration efficiency and mechanical properties of the fuel cell may be degraded. In this study, gadolinium-doped ceria nanopowder with $Al_2O_3$ and $Mn_2O_3$ as a reinforcing and electron trapping agents were synthesized by ultrasonic pyrolysis process. After firing, their microstructure and mechanical and electrical properties were investigated and compared with those of pure gadolinium-doped ceria specimen.

• 한국재료학회지
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• 제18권9호
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• pp.470-474
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• 2008

Composites of gadolinium-doped ceria/magnesia(CGO/MgO) were synthesized and characterized for the electrolytes of intermediate temperature solid oxide fuel cells. XRD and SEM results revealed that composite electrolytes consisted of their own phases after sintering at $1400^{\circ}C$ without noticeable solid solution of Mg into CGO. As the MgO content increased, the total electrical conductivity decreased, which might be attributed to the decrease of grain boundary conductivity, possibly due to the lowering of the continuity of the CGO grains and blocking effects of the insulating MgO phase. The space charge effect may not be a significant factor to affect the electrical conductivity of the CGO/MgO composites.

• 공업화학
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• 제21권4호
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• pp.401-404
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• 2010

GDC (Gadolinium doped ceria) 펠렛에 120 keV 및 5 MeV 에너지의 양성자 또는 제논 이온을 주입하였으며, 그 영향을 UV-vis 분광계, SEM 및 XRD를 이용하여 측정하였다. GDC 펠렛은 cubic fluorite 구조를 갖는 조밀한 소결체였으며, 갈색이었던 펠렛이 이온빔을 조사한 후 옅은 검은색을 띠기 시작하였으며, fluence가 증가함에 따라 색도 짙어졌다. XRD 패턴은 이온의 에너지 및 X선의 투과 깊이와 밀접한 관계가 있었으며, 120 keV의 양성자 빔을 조사한 표면 바로 아래층은 이온의 주입으로 결정 구조는 유지한 채 격자 상수가 증가하였다는 것을 관찰하였다.

• Journal of Electrochemical Science and Technology
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• 제2권1호
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• pp.32-38
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• 2011

The composite barium strontium cobalt ferrite (BSCF) cathodes were investigated in the intermediate temperature range of solid oxide fuel cells (SOFCs). The characteristics and electrochemical performances of composited BSCF/samarium doped ceria (SDC); BSCF/gadolinium doped ceria (GDC); and BSCF/SDC/GDC were compared to single BSCF cathode. The BSCF used in this study were synthesized using glycine nitrate process and mechanically mixing was used to fabricate a composite cathode. Using a composite form, the thermal expansion coefficient (TEC) could be reduced and BSCF/SDC/GDC exhibited the lowest TEC value at $18.95{\times}10^{-6}K^{-1}$. The electrochemical performance from half cells and single cells exhibited nearly the same trend. All the composite cathodes gave higher electrochemical performance than the single BSCF cathode (0.22 $Wcm^{-2}$); however, when two kinds of electrolyte were used (BSCF/SDC/GDC, 0.36$Wcm^{-2}$), the electrochemical performance was lower than when the BSCF/SDC (0.45 $Wcm^{-2}$) or BSCF/GDC (0.45 $Wcm^{-2}$) was applied as cathode ($650^{\circ}C$, 97%$H_2$/3%$H_2O$ to the anode and ambient air to the cathode).

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.108-108
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• 2003

• 한국세라믹학회지
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• 제53권5호
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• pp.489-493
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• 2016

Scandia ($Sc2O_3$)-stabilized zirconia (ScSZ) electrolyte-supported symmetrical solid oxide electrolyzer cells (SOECs), in which lanthanum strontium cobalt ferrite (LSCF)-gadolinia ($Gd_2O_3$)-doped ceria (GDC) composite materials are used as both the cathode and anode, were fabricated and their high temperature steam electrolysis (HTSE) performance was investigated. Current density-voltage curves were obtained for cells operated in 10% $H_2O$/90% Ar at 750, 800, and $850^{\circ}C$. It was possible to determine the ohmic, cathodic, and anodic contributions to the total overpotential using the three-electrode technique. The HTSE performance was significantly improved in the symmetrical cell with LSCF-GDC electrodes compared to the cell consisting of an Ni-YSZ cathode and LSCF-GDC anode. It was found that the overpotential due to the LSCF-GDC cathode largely decreased and, at a given current density, the total cell voltage decreased, which resulted in the enhanced hydrogen production rate in the symmetrical cell.

• 한국세라믹학회지
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• 제47권1호
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• pp.82-85
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• 2010

Recently, thin film processes for oxides and metal deposition, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), have been widely adapted to fabricate solid oxide fuel cells (SOFCs). In this paper, we presented two research area of the use of such techniques. Gadolinium doped ceria (GDC) showed high ionic conductivity and could guarantee operation at low temperature. But the electron conductivity at low oxygen partial pressure and the weak mechanical property have been significant problems. To solve these issues, we coated GDC electrolyte with a nano scale yittria-doped stabilized zirconium (YSZ) layer via atomic layer deposition (ALD). We expected that the thin YSZ layer could have functions of electron blocking and preventing ceria from the reduction atmosphere. Yittria-doped barium zirconium (BYZ) has several orders higher proton conductivity than oxide ion conductor as YSZ and also has relatively high chemical stability. The fabrication processes of BYZ is very sophisticated, especially the synthesis of thin-film BYZ. We discussed the detailed fabrication processes of BYZ as well as the deposition of electrode. This paper discusses possible cell structure and process flow to accommodate such films.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.184-186
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• 2009

Composites of LSCF($La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-\delta}$ and CGO(gadolinium doped ceria) is an efficient candidate cathode material with CGO electrolytes. In this study, LSCF with exact perovskite structure was synthesized by using solid state reaction(SSR) method. The optimized temperature to synthesize $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-\delta}$ with rhombohedral structure. was $1100^{\circ}C$. The polarization resistance of the LSCF/CGO(50:50 wt.%) was smaller than those of other composite cathodes. The analysis of the EIS data of LSCF/CGO suggests that the diffusion and adsorption-desorption of oxygen can be the key process in the cathodic reaction of SOFC using LSCF/CGO as cathode material.

• 한국세라믹학회지
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• 제42권9호
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• pp.637-644
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• 2005

In order to find a proper buffering material which can prohibit an unwanted interfacial reaction between anode and electrolyte of LSGM-based SOFC, we examined a gadolinium doped ceria and scandium doped zirconia as a candidate. For this examination, we investigated the microstructural and phase stability of the interface under different buffering layer conditions. According to the investigation, ceria based material induced a serious La diffusion out of the LSGM electrolyte resulted in the formation of very resistive $LaSrGa_3O_7$ phase at the interface. On the other hand zirconia based material was directly reacted with LSGM electrolyte and thus produced very resistive reaction products such as $La_2Zr_2O_7,\;Sr_2ZrO_4,\;LaSrGaO_4\;and\;LaSrGa_3O_7$. From this study we found that an improper buffering material induced the higher internal cell resistance rather than an interfacial stability.

• 한국세라믹학회지
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• 제47권2호
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• pp.199-204
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• 2010

A dual-phase ceramic membrane consisting of gadolinium-doped ceria (GDC) as an oxygen ion conducting phase and $MnCo_2O_4$ as an electron conducting phase was fabricated by sintering a GDC and $MnCo_2O_4$ powder mixture. The $MnCo_2O_4$ was found to maintain its spinel structure at temperatures lower than $1200^{\circ}C$. (Mn,Co)(Mn,Co)$O_4$ spinel, manganese and cobalt oxides formed in the sample sintered at $1300^{\circ}C$ in an air atmosphere. XRD analysis revealed that no reaction phases occurred between GDC and $MnCo_2O_4$ at $1200^{\circ}C$. The electrical conductivity did not exhibit a linear relationship with the $MnCo_2O_4$ content in the composite membranes, in accordance with percolation theory. It increased when more than 15 vol% of $MnCo_2O_4$ was added. The oxygen permeation fluxes of the composite membranes increased with increasing $MnCo_2O_4$ content and this can be explained by the increase in electrical conductivity. However, the oxygen permeation flux of the composite membranes appeared to be governed not only by electrical conductivity, but also by the microstructure, such as the grain size of the GDC matrix.