K₂NiF₄ type 층상 페롭스카이트 구조 La(Ca)₂Ni(Cu)O_4-_δ의 SOFC 양극 특성 및 결정구조 평가

명재하,홍연우,이미재,전대우,이영진,황종희,신태호,백종후,Myung, Jae-ha,Hong, Youn-Woo,Lee, Mi Jai,Jeon, Dae-Woo,Lee, Young-Jin,Hwang, Jonghee,Shin, Tae Ho,Paik, Jong Hoo 한국결정성장학회 2015 한국결정성장학회지 Vol.25 No.3

혼합이온 전도체인 $K_2NiF_4$-type 산화물인 $La(Ca)_2Ni(Cu)O_{4+{\delta}}$ 분말을 합성하여 결정구조 분석과 분말의 나노구조화에 따른 고체산화물 연료전지의 양극 성능을 비교 평가하였다. 이온 반경이 큰 Cu가 Ni 자리에 치환되어 Ni-O 팔면체 구조에서 c 축 방향으로 결정구조가 팽창하였으며, Ni-Cu의 Jahn-Teller 뒤틀림으로 산소이온 산화 환원 반응과 이온 전도도 특성에 영향을 주었다. 특히 나노구조의 $La(Ca)_2Ni(Cu)O_{4+{\delta}}$ 분말의 경우 표면 촉매성능이 향상되어 단위 전지 성능 향상 결과를 얻을 수 있었다. Ni-YSZ 음극 지지체에 8YSZ 전해질을 dip-coating한 후 $La(Ca)_2Ni(Cu)O_{4+{\delta}}$ 분말을 양극으로 도포하여 얻은 SOFC 단위성능 측정 결과 $800^{\circ}C$에서 $1w/cm^2$의 최대 출력 값을 얻을 수 있었다. $La_2NiO_{4+{\delta}}$ based oxides, a mixed electronic-ionic conductors (MIECs) with $K_2NiF_4$ type structure, have been considerably investigated in recent decades as electrode materials for advanced solid oxide fuel cells (SOFCs) due to their high electrical conductivity, and oxidation reduction reaction (ORR). In this study, structure properties of $La(Ca)_2Ni(Cu)O_{4+{\delta}}$ were studied as a potential cathode for intermediate temperature SOFCs (IT-SOFCs).

초고온용 발열체 (Mo₁₋xWx)Si₂의 산화거동에 대한 연구

이성철,명재하,김용남,전민석,이동원,오종민,김배연 한국결정성장학회 2020 韓國結晶成長學會誌 Vol.30 No.5

MoSi2, (Mo1/2W1/2)Si2, and WSi2 powders were synthesized by self-propagating high-temperature synthesis (SHS)method. The synthesized powders were heat-treated at 500, 1,000, 1,200, 1,300, 1,400, 1,500 and 1,600°C in ambientatmosphere. Oxidation of Mo-W silicide powder was found at low temperature of 500°C. XRD structure analysis and DTA/TG data showed that MoO3 was formed with 500°C heat treatment for 1 hour, and that it was α-cristobalite phase that was formed with 1200°C heat treatment, not α-quartz phase which is commonly found and stable at room temperature. Existence of W accelerated decomposition at both low and high temperature. Fully sintered MoSi2 and (Mo1/2W1/2)Si2 specimen did not show decomposition or weight loss by oxidation, with 1 hour heat treatment at either low or high temperature. Notably, it was difficult to sinter WSi2 because of oxidation reaction at low temperature. SHS 법으로 MoSi₂ 분말, (Mo1/2W1/2)Si₂ 분말 및 WSi₂ 분말을 합성하고 이 분말들을 500°C, 1,000°C, 1,200°C,1,300°C, 1,400°C, 1,500°C 및 1,600°C에서 열처리한 다음, 결정구조 및 열중량 변화 등을 관찰하였다. Mo-W-Si계의 silicide분말은 500°C의 저온에서도 산화 반응이 일어나며, 저온 산화 및 분해로 생성되는 결정상은 MoO3이었다. 1,200°C 이상에서 열처리를 한 경우에 분해반응으로 생성된 SiO₂의 결정상은 상온에서 흔히 관찰되는 α-quartz가 아닌 α-cristobalite 상으로 생성되었다. W이 포함되면 저온과 고온에서 분해 반응이 더 많이 일어나는 것으로 나타났으며, 분말을 성형하여 소결한 시편의 경우에 MoSi₂와 (Mo1/2W1/2)Si₂는 저온이나 고온에서 1시간 열처리를 하더라도 저온산화에 의한 분해와 그에 따른 질량 변화 반응을 관찰하기 어려웠지만 WSi₂는 저온 산화에 의하여 소결 자체가 어려웠다.

Oxide Materials with Reversible Exsolution and Incorporation

이찬우,명재하,유정준 한국에너지학회 2016 한국에너지공학회 학술발표회 Vol.2016 No.10

고체산화물 연료전지 연료극 및 전해질 미세구조 최적화

노종혁,명재하 한국화학공학회 2019 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.57 No.4

The performance and stability of solid oxide fuel cells (SOFCs) depend on the microstructure of the electrode and electrolyte. In anode, porosity and pore distribution affect the active site and fuel gas transfer. In an electrolyte, density and thickness determine the ohmic resistance. To optimizing these conditions, using costly method cannot be a suitable research plan for aiming at commercialization. To solve these drawbacks, we made high performance unit cells with low cost and highly efficient ceramic processes. We selected the NiO-YSZ cermet that is a commercial anode material and used facile methods like die pressing and dip coating process. The porosity of anode was controlled by the amount of carbon black (CB) pore former from 10 wt% to 20 wt% and final sintering temperature from 1350 oC to 1450 oC. To achieve a dense thin film electrolyte, the thickness and microstructure of electrolyte were controlled by changing the YSZ loading (vol%) of the slurry from 1 vol% to 5 vol. From results, we achieved the 40% porosity that is well known as an optimum value in Ni-YSZ anode, by adding 15wt% of CB and sintering at 1350 oC. YSZ electrolyte thickness was controllable from 2 µm to 28 µm and dense microstructure is formed at 3vol% of YSZ loading via dip coating process. Finally, a unit cell composed of Ni-YSZ anode with 40% porosity, YSZ electrolyte with a 22 µm thickness and LSM-YSZ cathode had a maximum power density of 1.426 Wcm-2 at 800 oC. 고체산화물 연료전지의 성능과 안정성은 전극의 기공률, 기공 분포와 전해질의 치밀도, 두께에 따라 결정 된다. 연료극의 기공률과 기공 분포는 활성면적와 연료 흐름에 영향을 주고, 전해질의 치밀한 미세구조와 두께는 단위전지의Ohmic 저항에 영향을 준다. 하지만 이를 위해 값 비싼 공정 장비를 이용하거나 여러 단계의 제작 공정이 추가 될 경우단위전지 제작비가 증가하므로 상업화를 목표로 하는 연구에는 적합하지 않다. 본 연구에서는 위와 같은 문제점들을해결하기 위하여 상용 소재 기반의 NiO-YSZ 연료극을 선정 후 간단한 혼합 방법 및 일축가압 성형법과 담금코팅(dip coating) 공정을 사용하여 저비용 고효율의 세라믹 공정 기반의 고성능 단위전지를 제작하였다. 연료극의 기공률은 기공형성제로서 사용되는 카본 블랙(CB, carbon black)의 첨가량(10~20 wt%)과 최종 소결온도(1350~1450 o C)를 변경하며 제어하였고, YSZ 전해질의 두께와 미세구조는 담금코팅 슬러리의 고상 분말량(YSZ, 1~5 vol%)을 제어하여 치밀한박막의 전해질을 구현하고자 하였다. 그 결과 Ni-YSZ 연료극에서 최적의 값으로 잘 알려진 40%의 기공률은 카본 블랙을 15 wt% 첨가하고최종소결온도를 1350 o C로설정함으로써얻을수있었다. 담금코팅을통한 YSZ 두께는 2~28 µm 까지 제어가 가능하였고, 3 vol%의 고상분말량에서 치밀한 전해질 미세구조가 형성되었다. 최종적으로 40%의 기공률을갖는 Ni-YSZ 연료극, 20 µm 두께의 치밀한 YSZ전해질, LSM-YSZ 공기극으로 구성된 단위전지는 800 o C에서1.426 Wcm-2의 우수한 성능을 얻을 수 있었다.

실린더형 MoSi₂계 발열체의 유도가열 적용

이성철,김요한,명재하,김배연,Lee, Sung-Chul,Kim, Yo Han,Myung, Jae-ha,Kim, Bae-Yeon 한국화학공학회 2019 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.57 No.4

본 연구에서는 슬립캐스팅 성형법을 이용하여 실린더형 $MoSi_2$계 세라믹 서스셉터를 개발하여 고온 유도가열에 적용시켰다. $MoSi_2$계 소재는 SHS법(Self-propagating High-temperature Synthesis)으로 합성하였고 XRD 분석을 통해 합성된 상과 결정구조를 확인하였다. 합성된 소재로 실린더 성형체를 제작하기 위해 슬립캐스팅을 진행하였고 슬립의 고형분 함량 및 유지시간을 조절하여 실린더 성형체의 두께를 제어하였다. 최종적으로 성형체 소결을 통해 유도가열 발열체를 제작하였고 열처리과정 중 표면에 형성된 $SiO_2$층은 SEM/EDS 분석을 통해 확인하였다. 서스셉터로서의 가열성능을 평가하기 위해 유도가열기로 일정한 출력을 인가하였을 때 $(Mo,W)Si_2$ 실린더 서스셉터의 표면온도를 측정하여 출력 2 kW를 인가하였을 때 발열특성을 분석하였으며, 서스셉터 표면의 최고 온도는 $1457^{\circ}C$, 평균 승온속도는 $19^{\circ}C/s$로 우수한 가열 특성을 나타냈다. In present study, the cylindrical susceptor by the slip casting method was designed to apply high-temperature induction heating by using $(Mo,W)Si_2$ ceramics. $MoSi_2$-based materials were synthesized by SHS (Self-propagating High-temperature Synthesis) method. The phase and crystal structure of $MoSi_2$-based materials were confirmed by XRD analysis. The shape of cylindrical mold was synthesized for various thickness by using the slip casting method. Finally, the susceptor for induction heating was processed by sintering and heat treatment to form $SiO_2$ layer, which was confirmed on the surface of susceptor by SEM/EDS analysis. To evaluate the heating performance of $(Mo,W)Si_2$ cylinder susceptor, we measured the maximum surface temperature and heating rate in comparison with the rod heating element under constantly applied power. The induction heating of the $(Mo,W)Si_2$ cylinder showed excellent heating performance, reaches the maximum temperature of $1457^{\circ}C$, with the average heating rate of $19^{\circ}C/s$ at 2 kW

신재생 하이브리드 이용 미래 에너지저장 기술

우상국,김선동,서두원,명재하,최현종,김태우,박성룡,황효정 한국에너지학회 2017 한국에너지공학회 학술발표회 Vol.2017 No.9

High-flexible Electrolyte Supported SOFCs via Transformable Tetragonal Phase of YSZ

Boram Won(원보람),Jaeha Myung(명재하) 한국신재생에너지학회 2021 한국신재생에너지학회 학술대회논문집 Vol.2021 No.7

The conventional ceramic based SOFCs (Solid Oxide fuel Cells) have limitations in commercialization, owing to the brittleness of solid electrolytes, which leads to mechanical fracture under external stress. Herein, a new concept of high-flexible electrolyte supported SOFCs with a bendable YSZ (yttria-stabilized zirconia) electrolyte is introduced to enhance the mechanical stability and long-term operation. YSZ consists of the transformable tetragonal phase, which transforms into monoclinic structure when the mechanical stress is applied. The phase transformation of YSZ is accompanied with 4% volume expansion, showing high flexibility and mechanical tolerance. In addition, the flexibility reduced the thickness of YSZ film up to ~17 ㎛, making the electrolyte film more bendable with minimum ohmic resistance. The flexibility of YSZ electrolyte was controlled by the microstructure, grain size, fraction of tetragonal phase, and tetragonality under various sintering condition. The flexible SOFC was prepared by using simple methods such as tape-casting and screen-printing. A single cell with Ni-YSZ anode (11 ㎛)|YSZ electrolyte (50 ㎛)|LSM-YSZ cathode (25 ㎛) exhibited maximum power density of 0.583 Wcm^-2 at 900℃ under wet H2. This study suggests the possible applications of SOFCs in mobile devices such as unmanned aircrafts without thermomechanical failure.

Synthesis and Characterization of B-site Co-doped Double Perovskites Sr₂Fe<SUB>1.5-x</SUB>Co<SUB>x</SUB>Mo<SUB>0.5</SUB>O<SUB>6-δ</SUB> (X=0, 0.05, 0.1, 0.2, 0.4, 0.5) as Electrodes for Symmetrical SOFCs

Hye-jin Jeon(전혜진),Jae-ha Myung(명재하) 한국신재생에너지학회 2021 한국신재생에너지학회 학술대회논문집 Vol.2021 No.7

Solid oxide fuel cells (SOFCs) are one of the most promising energy devices with great conversion efficiency; however, the conventional Ni based cermet electrodes have been suffered from catalyst agglomeration, carbon and sulfur poisoning. The symmetrical solid oxide fuel cells (SSOFCs), which use the same electrode materials at both anode and cathode, can overcome the carbon deposition and sulfur poisoning by simply reversing the gas flow. Sr2Fe_1.5Mo_0.5O_6-δ (SFM) showed promising redox stability and catalytic activity as electrode of SSOFCs. Herein, Co-doped Sr2(Fe_1.5-xCoxMo_0.5)O_6-δ (SFCM) has been synthesized by solid state reaction method (SSR) and studied toward application as electrodes for SSOFCs. The crystal structure, micro-structure, thermal expansion, electrochemical performance and stability under SOFC operating conditions have been characterized as a function of Co-doping amount. In the case of SFCM, the doped Co accelerates the exsolution of Co-Fe alloy nano-catalysts (CFNC) well dispersed on the matrix under the reduction atmosphere. However, the Co substitution results in increase of thermal expansion coefficient (TEC) and thermo-mechanical instability as electrodes. Via the investigation of adequate Co-doping amount, we developed innovative materials which represents high redox-stability and catalytic activity with high thermo-mechanical stability under the fuel cell operating conditions.

Surface decorated La0.43Ca0.37Ni0.06Ti0.94O3d as an anode functional layer for solid oxide fuel cell applications

정현권,김도엽,Bharat Sharma,노종혁,이강택,명재하 한국화학공학회 2020 Korean Journal of Chemical Engineering Vol.37 No.8

Surface decorated La0.43Ca0.37Ni0.06Ti0.94O3d (LCNT) perovskite oxide was investigated as an anode functional layer (AFL) for anode-supported solid oxide fuel cells (SOFCs). The surface exsolved Ni nano particles on LCNT scaffold enlarged electrochemically active triple phase boundaries (TPBs) without any agglomeration and mechanical failure. The Ni particles with 60 nm in diameter were homogeneously exsolved from LCNT perovskite. The Ni-YSZ anode supported cell with LCNT anode functional layer (AFL) exhibited a maximum power density of 0.94 W/cm2, similar to that of the conventional Ni-YSZ AFL cell at 900 oC. The activation polarization resistance of the LCNT AFL cell was effectively reduced compared to that of the Ni-YSZ AFL cell, though it had higher Ohmic resistance due to thicker YSZ electrolyte and lower electrical conductivity. Our study suggests the potential use of LCNT with exsolved nano particles as an active and durable AFL for high-temperature SOFCs.