• 한국세라믹학회지
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• 제37권5호
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• pp.479-490
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• 2000

The microstructure of Ni-YSZ composite as an anode of SOFC was investigated as a function of Ni content(10-70 vol%) in order to examine the correlation between microstructural-and electrical property. Image analysis based on quantitative microscopy theory was performed to quantify the microstructural property. We could get the informations about the size and distribution, contiguity and interfacial area of each phase or between the phases from the image analysis. According to the image analysis, contiguity between the same phae was mainly dependent on the amount of the phase while the contiguity between different phases was additionally influenced by the microstructural changes, especailly by the coarsening of the Ni phase. The whole length of pores perimeter was increased as Ni content increased, which indicated the overall microstructural evolution was mostly related with the coarsening of Ni phase. Ni-Ni interfacial area was also gradually increased as Ni content increased but controlled by pore phase at low Ni content region and by YSZ phase at intermediate Ni content region. These quantified microstructural properties were used to characterize the electrical properties of Ni-YSZ composite.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.422-425
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• 1999

Ultrafine NiO/YSZ (Yttria-Stabilized Zirconic) composite powders were prepared by using a glycine nitrate process (GNP) for anode material of solid oxide fuel cells. The specific surface areas of synthesized NiO/YSZ composite powders were examined with controlling pH of a precursor solution and the content of glycine. The binding of glycine with metal ions occurring in the precursor solution was analyzed by using FTIR. The characteristics of synthesized composite powders were examined with X-ray diffractometer, a BET method with $N_2$ absorption, scanning and transmission electron microscopies. Strongly acid precursor solution increased the specific surface area of the synthesized composite powders. This is suggested to be caused by the increased binding of metal ions and glycine under a strong acid solution of pH=0.5 that lets glycine consist of mainly the amine group of NH$_3$$^{+}$ After sintering and reducing treatment of NiO/YSZ composite powders synthesized by GNP, the Ni/YSZ pellet showed ideal microstructure very fine Ni Particles of 3-5${\mu}{\textrm}{m}$ were distributed uniformly and fine pores around Ni metal particles were formed, thus, leading to an increase of the triple phase boundary among gas, Ni and YSZ.Z.

• 한국세라믹학회지
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• 제38권5호
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• pp.466-473
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• 2001

Ni-YSZ 음극의 미세구조와 임피던스특성에 미치는 YSZ 입자크기 및 소결온도의 영향을 고찰하였다. 0.3~0.6$\mu\textrm{m}$의 미세한 NiO 분말을 사용할 경우에는 NiO 분말과 크기가 비슷한 미세한 YSZ 분말(TZ8Y, 0.3$\mu\textrm{m}$)을 첨가했을 때 NiO의 입성장을 억제하는 효과가 가장 크고 환원후 Ni의 입자크기를 미세하게 유지할 수 있는 미세구조를 형성하였다. 또한 미세한 YSZ 분말 (TZ8Y, 0.3$\mu\textrm{m}$)과 조대한 YSZ 분말(FYT13.0, 2$\mu\textrm{m}$)의 혼합비를 달리하여 후막을 제조하였을 때에 TZ8Y 분말만 첨가한 조성이 가장 낮은 분극 저항을 나타내었다. 한편 소결온도는 삼상계면의 양과 분극저항에 영향을 주었으며, 140$0^{\circ}C$에서 소결한 시편의 분극저항이 가장 낮은 값을 나타내었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.1080-1083
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• 2001

Ultrafine NiO/YSZ composite powders were prepared by using a glycine nitrate process for anode material of solid oxide fuel cells. The specific surface areas of synthesized NiO/YSZ composite powders were examined with controlling pH of a precursor solution and the content of glycine. The characteristics of synthesized composite powders were examined with X-ray diffractometer, a BET method with N$_2$absorption, scanning and transmission electron microscopy. The strongly acid precursor solution increased the specific surface area of the synthesized composite powders. This is suggested to be caused by the increased binding of metal ions and glycine under a strong acid solution of pH=0.5 that lets glycine consist of mainly the amine group of NH$_3$$\^$+/. After sintering and reducing treatment of NiO/YSZ composite powders synthesized by GNP, the Ni/YSZ pellet showed ideal micro-structure very fine Ni parties of 3-5${\mu}$m were distributed uniformly and fine pores around Ni metal particles were formed, thes, leading to an increase of the triple phase boundary among gas Ni and YSZ.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.31.2-31.2
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• 2011

We studied a method of manufacturing an anode to restrict contraction in reducing NiO/YSZ by uniformly mixing. In order to mix Ni and YSZ, a sub-micron Ni core surface was coated at high-speed by a mixture of nano-sized YSZ and a spherical core-shell was subsequently formed. The micron-sized core-shell anode powder was then heat treated at $400{\sim}1,450^{\circ}C$ in an air atmosphere and Ni was extruded and synthesized in nano-size. Subsequently, when the nano-sized mixture of the anode was heat treated and maintained at a temperature of $1,450^{\circ}C$, the anode was manufactured, where Ni and YSZ were uniformly distributed with the nano-structure. According to the nano-sized anode powder synthesis process, Ni particles were oxidized at $400{\sim}500^{\circ}C$ and became spherical by surface tension. In the case of the spherical core Ni powder, the heat treatment temperature rose to $1,250^{\circ}C$ and then a gap between the internal and external pressures occurred due to thermal and tensile stresses. A crack subsequently appeared on the surface, and the heat treatment temperature was increased continuously to increase the pressure gap and then the core Ni extruded as a nano-sized powder, Ni and YSZ uniformly distributed. It was found that the anode of 50~200 nm with a consistent structure obtained in this study has electric conductivity that is approximately 3 times larger than that of a commercial anode.

• 한국세라믹학회지
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• 제38권2호
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• pp.137-142
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• 2001

SOFC 음극으로 쓰이는 Ni-YSZ 복합체의 제조과정 중에 생기는 조성의 변화를 관찰하였다. XRD를 이용하여 복합체 부위별로 상분석한 결과 Ni-YSZ 복합체는 소결과정이나 환원처리시 복합체 내-외부간의 조성차가 일어나며 이로 인해 전기적 물성의 불균일성이 나타난다. 복합체 조성의 불균일성 및 전기적 물성의 불균일성은 주로 복합체를 구성하는 Ni 성분의 변화에 기인했는데 소결과정이나 환원과정시 Ni 성분이 기판으로 확산해가거나 기상으로 증발해버려 Ni 손실이 생기기 때문인 것으로 나타났다. Ni 성분의 손실은 열처리 온도와 시간에 비례하여 커졌으며 이로 인해 복합체의 전기적 물성도 악화되었다.

• 한국세라믹학회지
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• 제37권12호
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• pp.1140-1145
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• 2000

Ni의 함량이 서로 다른 Ni-YSZ 복합체를 100$0^{\circ}C$ 환원 분위기 하에서 열처리하며 시간에 따른 미세구조의 변화를 관찰하였다. Quantitative microscopy 이론을 응용한 화상분석 결과 Ni-YSZ 복합체의 미세구조는 열처리시 나타나는 Ni상의 미세구조 변화에 가장 큰 영향을 받고 있었다. 특히 Ni의 양이 많은 조성에서는 Ni 상간의 접촉이 많아 고상반응에 의한 미세구조의 변화가 심하였는데 이로 인해 복합체 미세구조의 안정화가 느리게 진행되었다. Ni-YSZ 복합체의 전기 전도도 역시 Ni상의 미세구조 변화에 큰 영향을 받았는데 복합체 전체 미세구조의 경시변화와는 달리 Ni상의 많은 조성보다는 Ni상의 percolation이 일어나는 조성 부근에서 더 큰 영향을 받았다. 이로 인해 Ni-YSZ의 전기 전도도는 Ni의 percolation threshold 부근 조성에서 안정화되는데 더 많은 시간을 요하였다.

• 한국수소및신에너지학회논문집
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• 제22권5호
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• pp.592-598
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• 2011

Electrode of solid oxide fuel cell must have sufficient porosity to allow gas transport to the interface with electrolyte effectively but high porosity has a negative impact on structural stability in electrode support. Thus, the upper limit of porosity is based on consideration of mechanical strength of electrode. In this study, the effect of microstructure of Ni-YSZ anode supported SOFC on the mechanical and electrical property was investigated. LSCF composite cathode and 8YSZ electrolyte were used. The porosity of the anode was modified by the amount of graphite powder and added graphite contents were 24, 18, 12 vol%, respectively. The higher the porosity, the better the electrical performance, $P_{max}$. While the flexural strength decreased with increasing the amount of graphite. But the rate of increase in electrical performance and the rate of decrease in mechanical strength were not directly proportional to amount of graphite. The optimum graphite content incorporating both electrical and mechanical performance was 18 vol%.

• 한국수소및신에너지학회논문집
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• 제21권6호
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• pp.526-532
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• 2010

The anode may inevitably undergo a number of reduction.oxidation (redox) cycles during solid oxide fuel cells (SOFCs) operation. The re-oxidation of Ni to NiO causes significant mechanical stress to be developed across the anode, which may destroy the integrity of the whole cell. In this study, the redox behavior of Ni-YSZ composite was examined at $800^{\circ}C$ using various characterization techniques.

• 한국세라믹학회지
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• 제44권10호
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• pp.589-595
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• 2007

Physical properties of sputtered YSZ thin film electrolytes on anode thin film by spray pyrolisis has been investigated to realize the porous electrode and dense electrolyte multilayer structure for micro solid oxide fuel cells. It is shown that for better crystallinity and density, YSZ need to be deposited at an elevated temperature. However, if pure NiO anode was used for high temperature deposition, massive defects such as spalling and delamination were induced due to high thermal expansion mismatch. By changing anode to NiOCGO composite, defects were significantly reduced even at high deposition temperature. Further research on realization of full cells by processing hybridization and cell performance characterization will be performed in near future.