초록 ▼

〇 본 연구개발은 고온 수증기 전기분해에 의한 수소제조기술로서, 800℃ 이상 고온의 수증기를 전기분해하여 높은 효율의 수소제조기술을 개발하는데 있다. 이를 위하여 고체산화물 전해셀용 소재(전극, 전해질, 연결재), 단위셀 내구성 향상 및 대용량 스택 설계-제조 기술을 개발하는데 목적이 있다.

〇 고온형 수증기 전해 장치용 소재 개발
V 페롭스카이스 (La_0.6Sr_0.4Ti_0.1Fe_0.9O₃)계 화합물 수소극 합성 및

〇 본 연구개발은 고온 수증기 전기분해에 의한 수소제조기술로서, 800℃ 이상 고온의 수증기를 전기분해하여 높은 효율의 수소제조기술을 개발하는데 있다. 이를 위하여 고체산화물 전해셀용 소재(전극, 전해질, 연결재), 단위셀 내구성 향상 및 대용량 스택 설계-제조 기술을 개발하는데 목적이 있다.

〇 고온형 수증기 전해 장치용 소재 개발
V 페롭스카이스 (La_0.6Sr_0.4Ti_0.1Fe_0.9O₃)계 화합물 수소극 합성 및 분극특성, 전기화학 특성 평가 완료
V LSCF 계 공기극을 이용해 분극저항(ASR) < 0.18 Ωcm² 달성

〇 고온형 수증기 전해 장치용 단위셀 내구성 향상기술 개발
V 단위셀의 초기 열화를 제어하였으며 10셀을 이용한 스택의 2000시간 장기 안정성 평가를 완료
V 단위셀의 전해질 또는 연결재 접합부위에서 발생할 수 있는 결함을 최소화 하였으며, 금속집전체 표면에 내산화 코팅을 하여 기존 75%/1000h에 달하는 열화율을 3%/1000h (250h 초기열화율 환산) 이내로 제어.

〇 고온형 수증기 전해 스택 설계 및 0.35 Nm³/h 스택 제작
V 수증기 전해 스택의 효율을 향상시키고 내구성을 높이기 위해 양쪽 끝이 막힌 튜브형을 고안하여 제작함.
V 3셀 스택으로 평가한 결과 스택 전류 효율은 97.61% 로 본 결과를 Int. J. Hydrogen Energ., 37 (2012) 78-83 에 게제
V Close-end형 튜브셀에 적합한 구조의 금속 manifold설계 및 제작하였으며, 0.35 Nm³/h 스택 제작

(출처 : 보고서 초록 4p)

Abstract ▼

IV. Results
1. Development of Unit Cell and Stack Module
〇 Development of Extrusion and Coating Process for Unit Cell
- Unit Cell Scale Up Technology
- Optimization of Drying Technology for Extruded Unit Cell
- Sealing Technology
- Co-Sintering of Cell and Ceramic Interconnector

IV. Results
1. Development of Unit Cell and Stack Module
〇 Development of Extrusion and Coating Process for Unit Cell
- Unit Cell Scale Up Technology
- Optimization of Drying Technology for Extruded Unit Cell
- Sealing Technology
- Co-Sintering of Cell and Ceramic Interconnector
〇 Fabrication of Anode(NiO-YSZ)-supported Electrolysis Cell
- Flat tubular electrolysis cells were fabricated with NiO-YSZ composite as a cathode support of electrolysis cell. The flat tubular cathode support was extruded and the unique design of both-end-closed tubular cell was developed by plugging the ends of the extruded support.
- Dip-coating and spray-coating techniques were applied to make dense structure of electrolyte and ceramic interconnect layers via co-firing. The ceramic interconnect layer coated on the cathode support showed the area specific resistance about 20-90 mΩcm², which was an excellent conducting property for interconnection material.

〇 Steam Electrolysis with Botton Cells
- Disk-shape of botton cell which was cut from the flat tubular cell showed 1.3 W/cm² in SOFC mode. The current density applied at 1.3V in SOEC mode was more than 1 A/cm², which corresponds to a hydrogen production rate of ~7 cc/min cm².
- Comparing the performance of ScSZ-based and YSZ-based cells, former one showed higher power output than later one in SOFC mode, which is attributed to the higher ionic conductivity of ScSZ than YSZ. The electrolysis performance of YSZ-based cell, however, was not inferior to ScSZ-based one.

〇 Steam Electrolysis with Flat-tubular Cells
- The steam electrolyzing properties of the both-end-closed flat tublar cell (Ni-YSZ/LSM) were successfully evaluated.
- Hydrogen was produced from the cell with an electrode (anode) area of 3x15 cm² at 7.2 L/hr and 9 L/hr at 800℃ an 850℃, respectively.
- Large-area cell with an anode area of 6x15 cm² showed a maximum power output of ~10W in SOFC mode. Hydrogen was produced at the rates of 6-8 L/hr by electrolyzing steam at the temperatures of 800℃ and 850℃.

〇 Development of Unit Cell Manufacturing and Operation Technology
- High-pressure and High-temperature Sealing Reliability
~ Multi-Stacking Technology and Design
- Stack Housing and Manifold
- Large Area Unit Cell

〇 Electrochemical Analysis for High Temperature Electrolysis
- Button Cell Electrochemical Analysis
- Effect of Gas Composition on the Performance of High Temperature Electrolysis
- Effect of Steam Concentration on the Performance of High Temperature Electrolysis

2. Interconnect and Air Electrode Materials for High Temperature Electrolsis Cell
〇 Dense donor-doped SrTiO₃ film (~30㎛) is fabricated by high temperature sintering (1400℃). Dense layer of YSTF (YxSr1-xTiyFe1-yO₃) and LSTF (LaxSr1-xTiyFe1-yO₃) is achieved successfully.

〇 Dense YSZ(~15㎛) and porous Ni-YSZ is fabricated by co-firing at 1400℃. Porous LSCF is also deposited by screen printing method. I-V curve and Ohmic, polarization resistance measured under different humidity. Enhancement of interface stability is attained by different GDC deposition process

3. Development of ceramic hydrogen/steam electodes and Polarization mechanism of high temperature electrolysis
〇 Characterization of La-Sr-Ti-O ceramic electrodes
- Titanates in perovskite-related structure have been prepared and the crystal structure, microstructure, conduction behavior and electrochemical performance were characterized.
- La₂Ti₂O₇ as n=2 of La₂Sr_n-2Ti_nO_3n+1 series showed the porous microstructure and good adherence with YSZ electrolyte but poor electrical conductivity and catalytic effects. The latter leads to the Hebb-Wagner polarization by the electron blocking supporting electrolytes and the mixed conduction mechanism in La₂Ti₂O₇ was successfully deconvoluted by impedance model analysis.
- La₂Sr₄Ti₆O₁₉ as n=6 of La₂Sr_n-2Ti_nO_3n+1 series has ideal fine porous microstructure and showed relatively stable electrochemical performance which is still too poor.
- La_0.4Sr_0.6TiO₃ and La_0.35Sr_0.65TiO₃ stoichiometric perovskites exhibited high conductivity of 10³ Ω^-1cm^-1, porous microstructure and good mechanical compatibility with YSZ but still poor electrochemical perfomance which is attributed to the poor catalytic effects for gas phase reactions.
- A-site deficient La_0.4Sr_0.4TiO₃ and La_0.35Sr_0.475TiO₃ exhibited liquid-phase sintering behavior preventing the gas electrode applications. The conductivity in the reducing
atmosphere (1 Ω^-1cm^-1) was less than that of the stoichiometic compounds but the conductivity in oxidizing atmosphere was higher.
- La_0.6Sr_0.4Ti_0.4Fe_0.9O₃ with possible high catalytic effects turned out unsuitable due to the liquid-phase formation, reactivity with YSZ, and decomposition in reducing atmosphere.
- Overall La-(Sr)-Ti-O compounds exhibited two different conduction patterns. Fundamental understanding of the oxides is necessary for the development of ceramic hydrogen/steam electrodes.

〇 Polarization mechanism of Ni-YSZ cermet electrodes and Ni_YSZ/YSZ/LSM solid oxide cells
- Electrolyte-supported Ni-YSZ symmetric cells confirmed the gas concentration impedance in the collecting nickel mesh similary as in the cermet support electrodes in single cells which decreases with increasing humidity. Similar concentration impedance was also observed in ceramic electrodes. Electrode reaction at Ni-YSZ electrodes is also enhanced with humidity which can be ascribed to the increased surface diffusion and reaction constant.

- High temperature electrolysis in Ni-YSZ/YSZ/LSM solid oxide cells decreases the LSM electrode polarization due to the increased oxygen activity which compensates the increased gas concentration polarization of Ni-YSZ electrodes. The LSM activity decreases thus in the fuel cell modes. High humidity operation (90% H₂O) results in the small polarizations both in SOEC and SOFC mode.

4. HTES Flow Channel Design and BOP Design/Fabrication Technology
〇 Computational Fluid Dynamics and Computer-Aided Modeling for Operation Condition
- Heat-induced deformation of SiC current collector is lowest compared to SUS: ZrH₂ and Al₂O₃ were used as cell and manifold materials, respectively.
- Computational Fluid Dynamics for HTES stack design indicated uniform pressure and fluid velocity throughout entire stack.

〇 Computer-aided modeling analysis for HTES stack structure
- Optimized stack structure design for fluid dynamics modeling and thermal stress evaluation.
- Computational modeling for parallel 5- and 10-stacks showed uniform fluid flow in each unit cell but thermal deformation was expected. On the other hand, series 4-stack modeling revealed uniform fluid distribution. 70% steam and 30% steam turned out to be more favorable for fluid distribution and electrochemical reaction.
- Experimental verification of computational modeling results by manifold fabrication and fluid flow experiment.

〇 BOP design and fabrication for HTES
- Literature search on HTES BOP and HTES system design by heat/mass balance evaluation.
- Computational modeling of steam heat exchanger and single pre-heater fabrication.
- Trial test of single BOP connected to HTES stack of Korea Institute of Energy Research

5. High temperature creep of ZrH₂ for fuel cell application
〇 Influence of the temperature on creep properties at high temperature
- Evaluation of bending strength at room and high temperature
- Development of jig for creep test at high temperature
- Preparation of jig using Al₂O₃ and SiC ceramics

〇 Influence of the load on creep properties at high temperature and fatigue properties
- Evaluation of creep test at vacuum an steam condition
- Influence of applied load on creep properties
- Applied load between 40MPa-60MPa
- Strain evaluation as function of a time

(출처 : SUMMARY 14p)