• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.1080-1083
• /
• 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.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1999.07a
• /
• pp.128-128
• /
• 1999

산소이온 전도체로 잘 알려진 Yttira-Stabilizd Ziroconia(TSZ)는 연료전지, oxygen pumps, chemical gas sensor 등 다양한 electrochemical divices에 이용되는 고체 전해질의 하나이다. 특히 YSZ는 oxygen 및 oxygen과 평형상태에 있는 gas들을 검출하는 sensor의 electrolyte로서 가장 많이 쓰이고 있다. 현재 상용화되어 있는 YSZ Sensor는 전통적인 bulk 형태의 ceramic으로 제작된 것으로 충분한 ionic conductivity를 얻기 위해서는 $600^{\circ}C$이상의 operating temperature를 필요로 하나 YSZ를 박막으로 제조시 낮은 operating temperature를 뿐만 아니라 sensor의 소형화, 낮은 ohmic loss 및 다양한 응용이 가능한 장점을 가질 수 있다. 본 실험에서는 산소 이온 전도체로서 8mol%-YSZ 고체전해질을 RF-magnetron bias sputtering 법을 이용하여 증착하였다. 제조된 YSZ 박막을 이용한 산소감응 센서셀 구조는 SiO2/Ni-NiO/Pt/YSZ/Pt-기판이다. 센서셀의 정상상태에서의 기전력(electromotive force ; EMF)을 산소분압(Po:1.013$\times$103Ta ~1.013$\times$105Pa)과 측정온도(30$0^{\circ}C$~$700^{\circ}C$)를 변화시키며 측정하였다. 이론적인 기전력과 측정값 사이의 편차는 Po:1.565$\times$104Pa 이하의 산소분압에서는 컸지만 이 이상의 분압에서는 이론치에 근접한 값을 가졌다. 증착한 YSZ와 Ni-NiO 박막의 구조는 X-ray diffractometer(XRD)를 이용하여 결정구조를 알아 보았고, TSZ 박막의 표면 morphology 관찰은 Scanning electron microscopy(SEM) 이용하였다. 박막의 조성분석은 X-ray energy dispersive analysis(EDX)을 사용하였다.

• Journal of the Korean Ceramic Society
• /
• v.38 no.1
• /
• pp.93-99
• /
• 2001

(La,Sr)MnO$_3$(LSM)-YSZ 복합체 양극에 있어서 소결온도 및 전극두께와 cathodic potential이 전극 특성에 미치는 영향을 고찰하였다. 양극의 소결은 삼상계면의 양을 결정하는 중요한 변수로 LSM 단미 양극과 YSZ가 40 wt% 포함된 LSM-YSZ 복합체 양극 모두 120$0^{\circ}C$에 소결했을 때 가장 낮은 분극저항을 나타내었다. 또한 양극 후막의 두께가 얇아지면 양극의 in-plane 저항이 증가하여 ohmic 저항이 증가하였는데, LSM-YSZ 복합체 양극의 경우 약 30$mu extrm{m}$ 정도의 전극두께가 가장 효과적인 전극 특성을 나타내었다. 한편, LSM-YSZ 복합체 양극에 -0.5 V의 cathodic potential을 인가함에 따라 양극에서 일어나는 산소환원반응의 활성이 증가하였는데, 1가 산소이온의 표면확산반응의 분극저항은 감소하였으나, 고주파수 영역에서 나타나는 산소이온전달반응의 저항은 거의 변화하지 않았다. 이것은 Mn의 환원에 의한 양극표면에 생성된 산소공공에 기인한다.

• Transactions of the Korean hydrogen and new energy society
• /
• v.28 no.6
• /
• pp.663-668
• /
• 2017

SOFC anode fabricated core-shell using machano-fusion method using core with submicron size Ni, nano size YSZ for shell. Using prepared core-shell, depending on the thickness of the shell, we studied how the characteristics of sintering and SOFC cell change by sintering the anode. The Ni-YSZ core-shell has a Ni core of 0.5 to $1.2{\mu}m$ over 2 to 7 YSZ of 15 to 20 nm is, and as the high speed mixing time increases, the YSZ number increases and the shell thickness becomes uniform increased. When the fuel electrode is manufactured with core-shell, it has superior sintering property, has grain of uniform size compared with the one synthesized by general mixing, the falling path is short, the conductors (electrons and ions) connection is excellent, the electrical conductivity has become excellent. The thicker the shell, the lower the electrical conductivity. When the thickness of shell ranged from 46 to 139 nm and 61 to 81 nm, the performance was the highest and the ASR was the smallest.

• Journal of the Korean Ceramic Society
• /
• v.43 no.12 s.295
• /
• pp.805-811
• /
• 2006

The microstructural changes in Ni/YSZ anode substrate and crack formation during Ni oxidation were investigated. The composition of as-sintered anodes was 56 wt% NiO+44 wt% YSZ and that of electrolyte was 8 mol% yttria. After complete reduction, specimens were oxidized in $N_2$ + air at $600\sim800^{\circ}C$. Oxygen partial pressure was controlled in between 0.05 atm and 0.2 atm $O_2$. When the anode was oxidized, at higher than $690^{\circ}C$, three layers were formed in the specimens. The first was fully oxidized layer(NiO/YSZ), the second was a mixed layer and the third, near-intact layer. Under $640^{\circ}C$ such distinctive layers were not observed. Cracks formed at electrolyte layer when weight gain attained at $65\sim75%$ of the total gain due to complete oxidation despite of different oxidation temperature and oxygen partial pressure.

• Transactions of the Korean hydrogen and new energy society
• /
• v.28 no.1
• /
• pp.40-46
• /
• 2017

We reviewed the electrical properties of SOFC anode manufactured using spherical Ni and nano YSZ powder. When core-shell is fabricated by using submicron Ni as core and nano-sized YSZ as shell for SOFC anode, the electrical conductivity of the $0.2{\mu}m$ Ni-YSZ core-shell was 3 times higher than that of $1.0{\mu}m$ NiO or $1.0{\mu}m$ Ni-YSZ. Hydrogen selectivity was similar at $800^{\circ}C$, but hydrogen selectivity and methane conversion rate under $750^{\circ}C$ was 10~25% higher, Power density was more than 2 times, ASR was about 1/3, when exposed to $H_2$ atmosphere at $750^{\circ}C$ for a long time, Ni particles did not have any growth or cut off conduction path.

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

• Journal of Powder Materials
• /
• v.18 no.5
• /
• pp.430-436
• /
• 2011

Joining of NiO-YSZ to 316 stainless steel was carried out with B-Ni2 brazing alloy (3 wt% Fe, 4.5 wt% Si, 3.2 wt% B, 7 wt% Cr, Ni-balance, m.p. 971-$999^{\circ}C$) to seal the NiO-YSZ anode/316 stainless steel interconnect structure in a SOFC. In the present research, interfacial (chemical) reactions during brazing at the NiO-YSZ/316 stainless steel interconnect were enhanced by the two processing methods, a) addition of an electroless nickel plate to NiO-YSZ as a coating or b) deposition of titanium layer onto NiO-YSZ by magnetron plasma sputtering method, with process variables and procedures optimized during the pre-processing. Brazing was performed in a cold-wall vacuum furnace at $1080^{\circ}C$. Post-brazing interfacial morphologies between NiO-YSZ and 316 stainless steel were examined by SEM and EDS methods. The results indicate that B-Ni2 brazing filler alloy was fused fully during brazing and continuous interfacial layer formation depended on the method of pre-coating NiO-YSZ. The inter-diffusion of elements was promoted by titanium-deposition: the diffusion reaction thickness of the interfacial area was reduced to less than 5 ${\mu}m$ compared to 100 ${\mu}m$ for electroless nickel-deposited NiO-YSZ cermet.

• Journal of the Korean Ceramic Society
• /
• v.36 no.4
• /
• pp.391-402
• /
• 1999

Characteristics of composite electrolytes which were prepared by coating a thin film of YSZ (yttria sta-bilized zirconia : (ZrO2)0.92 (Y2O3)0.08) on YDC (yttria doped ceria : Ce0.8Y0.2O1.9) with mixed conductivity have been investigated in order to develop the low-temperature solid oxide fuel cell. The thickness (t) of spin-coated YSZ thin films after the heat-treatment at 600$^{\circ}C$ was increased proportionally to the sol con-centrations (C) while the decrease in its thickness with the spin rate ($\omega$) could be expressed in the e-quation of ln t=9.49-0.53 ln $\omega$(0.99mol//s sol conc.) When the sol concentration and the spin rate being less than 0.99 mol/l and higher than 1000 rpm respectively reliable YSZ/YDC composite electrolytes could be obtained by multi-coating although several micro-cracks were observed in singly coated YSZ film surfaces. The dense YSZ film with a 1$\mu\textrm{m}$ thickness was prepared by coating of 0.99 mol/l YSZ sol five-times at 2000 rpm followed by heat-treatment at 1400$^{\circ}C$ for 2h, The adhesion between YSZ film and YDC substrate was found to be very good. The open circuit voltages of H2/O2 single cell with YSZ/YDC composite electrolytes were 0.79∼0.82 V at 800$^{\circ}C$ and 0.75∼0.77V at 900$^{\circ}C$ The open circuit voltage was inversely proportioned to the thickness ratio of YSZ thin film (1$\mu\textrm{m}$) to YDC substrate(0.28-2.22 mm)

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.1
• /
• pp.21-26
• /
• 2011

Ni-YSZ (Yttria Stabilized Zirconia) composite powders were fabricated by glycine nitrate process. The prepared powders were sintered at $1300{\sim}1400^{\circ}C$ for 4 h in air and reduced at $1000^{\circ}C$ for 2 h in a nitrogen and hydrogen atmosphere. The microstructure, electrical conductivity, thermal expansion and mechanical properties of the Ni-YSZ cermets have been investigated with respect to the volume contents of Ni. A porous microstructure consisting of homogeneously distributed Ni and YSZ phases together with well-connected grains was observed. It was found that the open porosity, electrical conductivity, thermal expansion and bending strength of the cermets are sensitive to the volume content of Ni. The Ni-YSZ cermet containing 40 vol% Ni was ascertained to be the optimum composition. This composition offers sufficient open porosity of more than 30 %, superior electrical conductivities of 917.4 S/cm at $1000^{\circ}C$ and a moderate average thermal expansion coefficient of $12.6{\times}10^{-6}^{\circ}C^{-1}$ between room temperature and $1000^{\circ}C$.