고체산화물 수전해전지에서 산소 분압 축적에 영향을 미치는 전해질의 이온ㆍ전자 전도도 역할 규명 = Understanding the Role of Ionic and Electronic Conductivities of Electrolytes in Oxygen Partial Pressure Build-Up of Solid Oxide Electrolysis Cells(SOECs)

다국어 초록 (Multilingual Abstract)

This study quantifies, in real time, the oxygen partial pressure(p_(O_2 ) ) that forms and accumulates inside SOEC electrolytes during operation and clarifies how the electrolyte’s ionic and electronic conductivities affect p_(O_2 ) build-up near the oxygen electrode and interfacial stability. A four-electrode setup incorporating a reference electrode and an embedded Pt probe enabled operando tracking of local electrolyte p_(O_2 ) independently of electrode overpotentials and ohmic losses.
To assess σ_i effects, LSM-based cells with YSZ were compared to YSZ/GdCeScSZ bilayer electrolytes. In YSZ, oxygen-electrode-side p_(O_2 ) increased with current density and reached 3.22 × 104 atm during long-term operation, exceeding p_(O_2)^cr(≈2.75 × 104 atm) and accompanied by delamination and intergranular fracture. The bilayer design reduced p_(O_2 ) and suppressed critical exceedance, indicating that improved σᵢ near the oxygen electrode mitigates p_(O_2 ) accumulation. However, partial delamination still occurred below p_(O_2)^cr, and La2Zr2O7 formation suggests an additional chemically driven degradation pathway.
To evaluate σ_e control with minimized interfacial reactions, LSCF/GDC cells with YSZ, 5CYSZ, and 8CYSZ were examined. Ce-doped CYSZ electrolytes exhibited markedly lower and more stable p_(O_2 ) during both short-term and long-term operation, accompanied by mitigated impedance growth and improved stability. However, increasing Ce content also increased the baseline ohmic ASR, which can penalize initial performance and limit high-current operating margins. In addition, more frequent/larger intrinsic pores observed in CYSZ imply that the mechanically defined limit (p_(O_2)^cr) may decrease due to enlarged defect sizes, even when operando p_(O_2 ) is effectively suppressed.
Overall, conductivity engineering is effective for suppressing excessive oxygen chemical potential build-up, while interfacial chemistry must be co-managed to ensure durable oxygen-electrode/electrolyte interfaces under high-current-density SOEC operation; furthermore, defect-controlled mechanical limits should be considered alongside transport-property optimization.

목차 (Table of Contents)

• 1. 서론 1
• 1) 연구 배경 및 필요성 1
• 2) 고체산화물 수전해전지 6
• 2-1. 고체산화물 수전해전지(SOEC)의 작동 원리 및 특성 6
• 2-2. 고체산화물 수전해전지(SOEC)의 구성요소 9
• 3) 고체산화물 수전해전지의 공기극/전해질 계면 박리 현상 13
• 3-1. 전해질 내부 산소 화학포텐셜·전위 분포의 이론적 분석 13
• 3-2. 공기극/전해질 계면 박리가 발생하는 산소 분압의 임계값 21
• 3-3. 전해질 이온전도도가 내부 p_(O_2 ) 축적에 미치는 영향 25
• 3-4. 전해질 전자전도도가 내부 p_(O_2 ) 축적에 미치는 영향 28
• 3. 실험방법 31
• 1) 실시간 내부 산소 분압 측정을 위한 4전극 시스템 31
• 2) 4전극 전지 제작 34
• 3) 실험 조건 38
• 3. 결과 및 고찰 42
• 1) 전해질의 이온전도도 차이에 의한 내부 p_(O_2 ) 거동 42
• 1-1. GdCeScSZ 전해질의 상 안정성 및 적용 근거 42
• 1-2. 단기 구동에서의 내부 p_(O_2 ) 거동 비교 45
• 1-3. 장기 구동에서의 내부 p_(O_2 ) 거동 비교 50
• 1-4. 장기 구동 전·후 전기화학 성능 비교 55
• 1-5. 사후분석 64
• 2) 전해질의 전자전도도 차이에 의한 내부 p_(O_2 ) 거동 71
• 2-1. CYSZ 전해질의 상 안정성 및 적용 근거 71
• 2-2. 단기 구동에서의 내부 p_(O_2 ) 거동 비교 73
• 2-3. 장기 구동에서의 내부 p_(O_2 ) 거동 비교 80
• 2-4. 장기 구동 전·후 전기화학 성능 비교 86
• 2-5. 사후분석 98
• 4. 결론 102
• 참고문헌 106
• Abstract 117
• Acknowledgment 120