Conditioning Effects on LSM-YSZ Cathodes for Thin-film SOFCs

Lee You-Kee,Visco Steven J. The Korean Electrochemical Society 1999 한국전기화학회지 Vol.2 No.4

[ $50/50 vol\%$ ] LSM-YSZ의 양극은 콜로이드 증착법에 의해 YSZ 전해질상에 증착하였다. 양극 특성은 주사전자현미경과 임피던스 분석기에 의해 고찰하였다. LSM-YSZ양극의 제조 조건에 따른 영향을 관찰하였으며, 그 영향에 대한 개선책이 고체산화물 연료전지의 성능향상을 위해 제시되었다. 임피던스에 대한 온도, YSZ전해질로의 양극 접착에 대한 표면 오염, 사용하는 Pt 페이스트, 미세구조에 대한 곡표면에 가해진 연무질 분사기술과 셀과 셀의 변동성에 대한 영향들은 각각 $900^{\circ}C$ 측정, YSZ표면 연마, 일단의 Pt페이스트 사용, 평편한 YSZ판의 사용과 일관된 절차와 기술의 사용에 의해 해결되었다. 이때 재현성 있는 임피던스 스펙트럼들이 향상된 셀을 사용함으로써 얻어졌고, $900^{\circ}C$에서 (공기)LSM-YSZ/YSZ/LSM-YSZ(공기) 셀에 대해 측정된 전형적인 임피던스 스펙트럼들은 2개의 불완전한 호로 구성되었다. 또한 LSM-YSZ 양극의 임피던스 특성은 촉매층, 양극 조성, 인가 전류 등과 같은 실험 조건들에 의해서도 영향을 받았다. Composite cathodes of $50/50\;vol\%$ LSM-YSZ $(La_{-x}Sr_xMnO_3-yttria\;stabilized\;zirconia)$ were deposited onto dense YSZ electrolytes by colloidal deposition technique. The cathode characteristics were then examined by scanning electron microscopy (SEM) and studied by ac-impedance spectroscopy (IS). The conditioning effects on LSM-YSZ cathodes were seen and remedies for these effects were noted in order to improve the performance of a solid oxide fuel cell (SOFC). The effects of temperature on impedance, surface contamination on cathode bonding to YSZ electrolyte, changing Pt paste, aerosol spray technique applied to curved surface on microstructure and cell to cell variability were solved by testing at $900^{\circ}C$, sanding the YSZ surface, using only one batch of Pt paste, using flat YSZ plates and using consistent procedures and techniques, respectively. And then, reproducible impedance spectra were confirmed by using the improved cell and the typical spectra measured for an (air)LSM-YSZ/YSZ/LSM-YSZ(air) cell at $900^{\circ}C$ were composed of two depressed arcs. Impedance characteristics of the LSM-YSZ cathodes were also affected by experimental conditions such as catalytic interlayer, composite cathode compositions and applied current.

Three-dimensional thermal stress analysis of the re-oxidized Ni-YSZ anode functional layer in solid oxide fuel cells

Kim, Jun Woo,Bae, Kiho,Kim, Hyun Joong,Son, Ji-won,Kim, Namkeun,Stenfelt, Stefan,Prinz, Fritz B.,Shim, Joon Hyung Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.752 No.-

<P><B>Abstract</B></P> <P>Nickel-yttria-stabilized zirconia (Ni-YSZ) cermet is widely used as an anode material in solid oxide fuel cells (SOFCs); however, Ni re-oxidation causes critical problems due to volume expansion, which causes high thermal stress. We fabricated a Ni-YSZ anode functional layer (AFL), which is an essential component in high-performance SOFCs, and re-oxidized it to investigate the related three-dimensional (3D) microstructural and thermo-mechanical effects. A 3D model of the re-oxidized AFL was generated using focused ion beam-scanning electron microscope (FIB-SEM) tomography. Re-oxidation of the Ni phase caused significant volumetric expansion, which was confirmed via image analysis and calculation of the volume fraction, connectivity, and two-phase boundary density. Finite element analysis (FEA) with simulated heating to 500–900 °C confirmed that the thermal stress in re-oxidized Ni-YSZ is concentrated at the boundaries between YSZ and re-oxidized NiO (nickel oxide). NiO is subjected to more stress than YSZ. Stress exceeding the fracture stress of 8 mol% YSZ appears primarily at 800 °C or higher. The stress is also more severe near the electrolyte-anode boundary than in the Ni-YSZ cermet and the YSZ regions. This may be responsible for the electrolyte membrane delamination and fracture that are observed during high-temperature operation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Re-oxidized NiO-YSZ was 3D-reconstructed via FIB-SEM tomography. </LI> <LI> Re-oxidation of Ni-YSZ removes pores via Ni volume expansion. </LI> <LI> The NiO-YSZ interface and the YSZ electrolyte exhibit high thermal stress. </LI> <LI> Thermal stresses greater than the fracture stress of YSZ appear at some interfaces. </LI> </UL> </P>

Prpperties of YSZ thin films deposited by RF magnetron sputtering

Lee, You-Kee 위덕대학교 산업기술연구소 2004 산업기술연구소 논문집 Vol.8 No.1

고주파 마그네트론 스퍼터링법으로 제조된 3mol%와 8mol% YSZ 박막의 스퍼터링 가스 내의 산소농도, 기판온도 및 Ar 압력에 따른 미세조직 및 광학적 특성을 조사하였다. 제조된 박막과 타게트의 결정구조는 서로 상이하게 나타났다. 3mol% YSZ 박막의 경우 스퍼터링 가스 내의 산소농도가 증가함에 따라 grain-like particle의 크기가 감소하였지만 8mol% YSZ 박막의 경우는 증가하는 경향을 보여주었으며, 8mol% YSZ 박막의 투과율은 3mol% YSZ 박막의 두께보다 더 두꺼운 두께에도 불구하고 더 높았다. 3mol% YSZ 박막의 굴절률은 스퍼터링 가스 내의 산소농도가 증가함에 따라 증가하였지만 8mol% YSZ 박막의 경우는 감소하는 경향을 보여주었다. 또한 8mol% YSZ 박막의 투과율은 기판온도 및 Ar 압력에 크게 영향을 받지 않았지만 굴절률은 큰 영향을 받았다. The effects of the O_(2) concentration in the sputtering gas mixture, substrate temperature and Ar pressure on the structural and optical properties of 3mol% YSZ and 8mol% YSZ thin films deposited by RF magnetron sputtering were investigated. The films were observed to have various crystal structures with different compositions in accordance with the type of the target materials. The size of fine grain-like particles decreased with increasing the O_(2) concentration in the sputtering gas in the case of 3mol% YSZ, while it increased in the case of 8mol% YSZ. However, the average optical transmission of 8mol% YSZ, despite of thicker thickness, was higher than that of 3mol% YSZ. Furthermore, the values of refractive index of 3mol% YSZ increased with increasing the O_(2) concentration in the sputtering gas on the contrary to those of the 8mol% YSZ. However, the transmission spectra of 8mol% YSZ films were not strongly influenced by the substrate temperature and Ar pressure, whereas the refractive index of the YSZ films were strongly affected by the sputtering parameters.

박막 고체산화물 연료전지용 이트리아 안정화 지르코니아 전해질 연마표면상의 공기극 성능

이유기,Lee, Yu-Gi 한국재료학회 2001 한국재료학회지 Vol.11 No.4

50/50 vol% LSM-YSZ (La$_{1-x}$Sr$_{x}$MnO$_3$-yttria stabilized zirconia)의 복합공기극이 콜로이드 증착법에 의해 연마된 YSZ 전해질상에 증착되었다. 그 전극 특성은 주사전자현미경, X선회절과 임피던스 분석기에 의해 연구되어졌다. 90$0^{\circ}C$에서 공기/LSM -YSZ/YSZ/Pt/공기 셀에 대해 측정된 전형적인 임피던스 스펙트럼들은 2개의 불완전한 호(depressed arc)로 구성되었다. LSM 전극에 대한 YSZ의 첨가는 전극내의 삼상계(TPB) 영역을 증가시켰으며, 이것이 LSM-YSZ 복합공기극의 비저항을 감소시켰다. 또한 전해질 표면의 불순물 제거와 TPB 길이의 증가를 위한 전해질 표면연마는 공기극의 비저항을 훨씬 더 감소시켰다. LSM-YSZ 공기극의 비저항은 작동온도, 공기극의 조성과 입자크기, 인가전류 및 전해질의 표면거칠기에 의해 큰 영향을 받았다. 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.

LSM과 YSZ의 분말크기 및 분말크기비가 SOFC의 양극특성에 미치는 영향

김재동,김구대,박지애 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.3

The LSM-YSZ composite electrode as a mixture of LSM and YSZ shows percolation characteristics. It was identified that the polarization resistance of LSM-YSZ composite electrode depend on YSZ connectivity by changing powder size ratio of the DLSM/DYSZ. That is, YSZ in composite electrode showed low electrochemical activity without YSZ connectivity. However, the polarization resistance decreased abruptly with YSZ connectivity due to high electrochemical activity of YSZ in composite electrode. Because the amount of three phase boundary is dependent on LSM and YSZ particle size, the polarization resistance of cathode decreases as LSM and YSZ particle size decreases.

초전도 테이프 제작을 위한 니켈기판 상의 산화물 박막 증찰

김호섭,고락길,정준기,하홍수,송규정,박찬,Kim, Ho-Sup,Shi, Dongqui,Ko, Rock-Kil,Chung, Jun-Ki,Ha, Hong-Soo,Song, Kyu-Jeong,Park, Chan 한국전기전자재료학회 2004 전기전자재료학회논문지 Vol.17 No.12

High temperature superconducting coated conductor has a structure of <protecting layer>/<superconducting layer>/<buffer layer>/<metallic substrate>. The buffer layer consists of multi-layer, this study reports the deposition method and optimal deposition conditions of YSZ(Yttria-stabilized zirconia) layer which plays a important part in preventing the elements of substrate from diffusing into the superconducting layer. YSZ layer was deposited by DC reactive sputtering technique using water vapor for oxidizing deposited elements on substrate. To investigate optimal thickness of YSZ film, four YSZ/CeO$_2$/Ni samples with different YSZ thickness(130 nm, 260 nm, 390 nm, and 650 nm) were prepared. The SEM image showed that the surface of YSZ layer was getting to be rougher as YSZ layer was getting thicker and the growth mode of YSZ layer was columnar grain growth. After CeO$_2$ layer was deposited with the same thickness of 18.3 nm on each four samples, YBCO layer was deposited by PLD method with the thickness of 300 nm. The critical currents of four samples were 0, 6 A, 7.5 A, and 5 A respectively. This shows that as YSZ layer is getting thicker, YSZ layer plays a good role as a diffusion barrier but the surface of YSZ layer is getting rougher.

칼슘이 첨가된 란탄-아크롬산 염과 이트리아 안정화 지르코니아 계면간의 반응

최진삼,Choe, Jin-Sam 한국재료학회 2001 한국재료학회지 Vol.11 No.6

The ceramic diffusion coupling with the green body of calcium-doped lanthanum chromite(La$_{0.8}$Ca$_{0.2}$CrO$_3$CLC- G) and sintered calcium-doped lanthanum chromite(La$_{0.8}$Ca$_{0.2}$CrO$_3$ CLC) by Pechini's method on yttria stabilized zirconia(YSZ) plate has been investigated. The X-ray diffraction pattern of CLC sides at the reacted CLC-G/ CLC and CLC/YSZ interface were identified as La$_{1-x}$ Ca$_{x}$CrO$_3$ and the unreacted YSZ side was cubic-ZrO$_2$ at the treated condition, 1300~1500 C for 10 hr in air, respectively. The order of migration components between CLC/YSZ interface was Zr>La>>Cr>>>Ca and these changes were not dependent upon the treated conditions. The grain shape and size at the interface of CLC-G/CLC was appeared to have a uniform distribution with increasing temperature. The bonding reaction of YSZ/CLC was occurred without a large amount change of the compositions in SEM photos.os.otos.os. Pechini방법으로 제조한 La$_{0.8}$Ca$_{0.2}$CrO$_3$CLC소결체와 La$_{0.8}$Ca$_{0.2}$CrO$_3$CLC-Green체를 YSZ에 적층한 후 온도의 함수로 계면에서의 미세구조와 성분이동 등의 거동을 고찰하였다. CLC-G/CLC와 CLC/YSZ계면에서의 CLC면은 반응온도에 상관없이 XRD 관찰에서 주상은 La$_{1-x}$ Ca$_{x}$CrO$_3$그리고 CLC와 반응하지 않은 YSZ면의 결정 상은 cubic-ZrO$_2$으로 각각 나타났다. CLC/YSZ반응 계면의 성분이동은 Zr > La>>Cr>>>Ca 순이었으며, 온도에 따른 개개 성분의 이동도 차이는 크지 않았다. CLC/YSZ계면간의 결합은 계면성분간의 과다한 성분이동 없이 현 연구의 온도전체에 걸쳐 가능한 것으로 나타났다. CLC-G/CLC간의 SEM미세구조는 결합 면을 경계로 저온에서는 결정의 입자크기 차이를 보이다가 온도가 증가할수록 균일화되는 경향을 보였다.였다. 보였다.였다.

LSMC-YSZ Composite 양극의 임피던스 특성

김재동,김구대,문지웅,김창은,이동아 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.9

YSZ와 계면반응하지 않는 ${(La_{0.75}Sr_{0.25})}_{0.95}Mn_{0.8 }Co_{0.2}O_3$에 전해질 물질인 YSZ를 첨가하여 양극의 분극특성을 고찰하였다. LSMC에 YSZ를 첨가함에 따라 삼상계면(Three Phase Boundary)이 증가하고, 분극저항이 감소하여 60 : 40wt% 비에서 최소값을 나타내었다. LSMC-YSZ composite 전극은 $1200^{\circ}C$ 에서 소결하여 최소의 분극저항을 나타내었고, 정전용량의 값은 소결온도의 증가에 따라 증가하였다. The polarization characteristics of the cathodes were discussed which were composed YSZ and ${(La_{0.75 }Sr_{0.25 })}_{0.95}Mn_{0.8 }Co_{0.2}O_3$ The three-phase-boundary length increased with the addition of YSN resulting in the minimum po-larization resistance at 60(LSMC) : 40(YSZ) wt% When LSMC-YSZ compoiste cathodes was sintered at $1200^{\circ}C$ minimum polarization resistance was observed and the capacitace increased with increasing sintering tem-perature.

Ductile Mode Machining of the Micro Pattern Made on YSZ Using Ultra-precision Shaping with a Diamond Tool

최환진,전은채,제태진,김정환,최대희,신보성,정우철,이윤희 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.12

Yttria stabilized zirconia (YSZ), which is a ceramic material, has a number of applications such as a refractory, thermal barrier coating and as a solid electrolyte for a solid oxide fuel cell (SOFC). Micro patterning the YSZ can increase the efficiency of the SOFC, but YSZ is difficult to mechanically machin. A few researchers have reported that an ultra-fine pattern can be mechanically machined on ceramic materials with no brittle fracture with a depth of cut close to sub-micrometers (called ductile mode machining). In the present study, the conditions for ductile mode machining of YSZ were studied. A 3-axis ultra-precision machine system and 90 diamond tool were employed to machine a micro pattern on YSZ. At first, when YSZ was machined with a depth of cut of 1 μm and 10 passes, the micro pattern was entirely fractured due to the brittleness of YSZ. Next, the micro pattern was machined with a depth of cut of 1 μm and 1 pass to verify how multi-pass machining affected the brittle fracture. A sparse brittle fracture occurred, which meant the depth of cut of 1 μm was too large for ductile mode machining. A mix of ductile mode machining and brittle mode machining was observed. Thirdly, when YSZ was machined with a depth of cut of 0.5 μm by 20 passes, the micro pattern was clearly machined with ductile mode machining. Thus, a transition point between ductile mode machining and brittle mode machining should exist at a depth of cut between 0.5 μm and 1 μm. A nanoscrach test was used to determine the transition point. The transition point was found to be 875 nm by analyzing the lateral force and the machined surface.

알루미나에 YSZ가 나노코팅된 층상형 시스템의 인덴테이션 특성평가

김상겸,김태우,김철,신태호,한인섭,우상국,이기성,Kim, Sang-Kyum,Kim, Tae-Woo,Kim, Chul,Shin, Tae-Ho,Han, In-Sub,Woo, Sang-Kuk,Lee, Kee-Sung 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.1

전자 범 물리적 증착법(Electron Beam Physical Vaper Deposition, EB-PVD)으로 알루미나 상용기판 위에 나노 크기의 YSZ입자를 포함하고 있는 층을 코팅하여 층상형 시스템을 제조하였으며, 이때 기판층의 온도를 600, 700, $800^{circ}C$로 변화시켜 증착되는 YSZ층이 서로 다른 미세구조가 형성되도록 제어하여, 코팅층 미세구조의 변화에 따른 인덴데이션 거동을 고찰하였다 인덴테이션 거동으로는 비커스 인덴테이션과 헤르찌안 인덴테이션으로 피라미드형 압자 혹은 초경 구를 압입하였으며 압입 하중 및 코링층 구조에 따른 경도와 인덴테이션 응력-변형률 곡선을 구하였고, 미세구조와 하중의 증가에 따른 손상 및 파괴거동을 고찰하였다. 기판층의 온도가 향상됨에 따라 증착된 입자의 크기가 보다 증가하고 각진 입자가 형성됨을 알 수 있었고, 서로 다른 미세구조가 인덴테이션 거동에 영향을 주어, $800^{circ}C$에서 증착된 YSZ/A12달 구조가 상대적으로 우수한 특성을 나타내었다. YSZ layer containing nano-sized particles has been deposited on the commercial A1203 substrate by Electron Beam Physical Vapor Deposition (EB-PVD). The role of coating rnjcrostructures of YSZ to indentation damage is studied. The different coating microsouctures are prepared by varying the substrate temperatures from $600^{circ}C$ to $800^{circ}C$ during the deposition. Microhardness test and Hertzian indentation are conducted on the $YSZ/Al_{2}O_{3}$ layered systems. The damage and flilure behaviors have been investigated according to the effect of microstructures and indentation loads. With increasing the substrate temperature during EB-PVD, the overall grain sizes are coarser and more faceted, which microsoucture ultimately influences on the indentation behavior, thus, YSZ/Al_{2}O_{3}$ layered system prepared at the substrate temperature of $800^{circ}C$ shows relatively higher damage tolerance.