표제지

국문 초록

목차

제1장 서론 15

제2장 이론적 배경 17

2.1. 고체산화물연료전지 (SOFC) 17

2.1.1. SOFC 개요 17

2.1.2. SOFC 작동원리 20

2.1.3. SOFC 구성 23

2.2. 지르코니아 (ZrO₂) 25

2.2.1. ZrO₂ 소재 특성 25

2.2.2. 정방정상 상전이특성 26

제3장 Y₂O₃-ZrO₂계 고유연성 전해질 지지체 기반 고체산화물 연료전지 30

3.1. 서론 30

3.2. 실험방법 35

3.2.1. 고유연성 전해질 지지체 제작 35

3.2.2. 전해질 지지체 특성 평가 42

3.2.3. 전해질 지지체형 고유연성 SOFC 개발 50

3.3. 결과 및 고찰 53

3.3.1. 고유연성 전해질 지지체 제작 53

3.3.2. 고유연성 전해질 지지체 특성 61

3.3.3. 전해질 지지체형 고유연성 SOFC 개발 76

3.3.4. 연료전지 성능 82

제4장 Sc₂O₃-ZrO₂계 고유연성 고이온전도성 전해질 개발 86

4.1. 서론 86

4.2. 실험방법 90

4.2.1. Sol-gel법을 통한 소재 합성 90

4.3. 결과 및 고찰 94

4.3.1. 소재 합성 최적화 94

4.3.2. 상 분석 101

4.3.3. 기계적 유연성 119

제5장 종합결론 121

참고문헌 123

Abstract 127

Table 3.1. Composition of YSZ tape-casting slurry. 38

Table 3.2. Control of 3YSZ electrolyte thickness depending on blade height. Electrolyte supports were sintered at 1450℃. 57

Table 3.3. Refinement of XRD data in Fig. 3.19. 67

Table 3.4. Materials for highly flexible solid oxide fuel cells. 81

Table 4.1. Composition of prepared electrolyte materials in this work. 92

Table 4.2. Raman peaks and vibrational modes of tetragonal ZrO₂. 108

Table 4.3. Crystallographic characterization of the powders sintered at 900℃. 109

Table 4.4. Refinement of XRD data in Fig. 4.9. 116

Figure 1.1. Overview of fuel cell technology. 19

Figure 1.2. Schematic of SOFC system. 22

Figure 1.3. Typical configuration of planar design (a) and tubular design (b) of SOFC. 24

Figure 1.4. Schematic illustration of insertion of the yttrium oxide inside the zirconia oxide lattice. 27

Figure 1.5. Schematic illustration of stress-induced phase transformation from tetragonal to monoclinic structure. 28

Figure 1.6. Schematic illustration of stress-induced phase transformation. 29

Figure 3.1. Phase diagram for the ZrO2-YO1.5 system. 33

Figure 3.2. Photograph of 3YSZ and 8YSZ disk-type thin film (~22 μm) when the film is bent at room temperature and schematics of its maximum bending angle. 34

Figure 3.3. Flow diagram for fabrication of electrolyte support by tape casting. 36

Figure 3.4. Composition of YSZ tape-casting slurry. 37

Figure 3.5. Photograph of sintered 3YSZ electrolyte with cracks. 40

Figure 3.6. Schematic diagram of sintering processes. 41

Figure 3.7. Photographs of prepared specimens for three-point bending test. 44

Figure 3.8. SEM images of prepared specimens for three-point bending test. 45

Figure 3.9. Photographs showing a three-point bending test on a UTM. 46

Figure 3.10. Schematic illustration of 3-point flexure test. 47

Figure 3.11. Schematic illustration of DC 4-probe measurement for bar type sample. 49

Figure 3.12. Schematic illustration of single cell operating condition. 52

Figure 3.13. Photographs of dispersion test for 3YSZ tape casting slurry. (E＝ethanol and T＝toluene). 55

Figure 3.14. Composition of 3YSZ tape-casting slurry and photographs of 3YSZ green sheets. 56

Figure 3.15. Photograph of 3YSZ electrolytes sintered at 1450℃ for 6h. 58

Figure 3.16. Cross-sectional SEM images of 3YSZ electrolytes made of optimized green tape. 59

Figure 3.17. SEM images of (a) the cross section and (b) the surface of 3YSZ electrolytes made of green tape that are not optimized. 60

Figure 3.18. Structure and phase analysis of 3YSZ films sintered at 1350 (3YSZ_1350), 1450 (3YSZ_1450) and 1550℃ (3YSZ_1550) for 6 h. (a) Tetragonality, (b) crystallite size, (c) XRD... 63

Figure 3.19. Refined XRD patterns of prepared 3YSZ films sintered at (a) 1350, (b) 1450, and (c) 1550℃. 64

Figure 3.20. Types of tetragonal phase: transformable (t) and non-transformable (t') tetragonal phase. 65

Figure 3.21. SEM image of 3YSZ film sintered at 1350, 1450, and 1550℃. 66

Figure 3.22. Mechanical property characterization of 3YSZ and 8YSZ films. (a) Relationship between thickness and bending strength, (b) relationship between the fraction of tetragonal phase... 70

Figure 3.23. Cross-sectional SEM images of symmetrical cell samples and electrolyte thickness. Half-cells were prepared with 3YSZ electrolyte sintered at (a) 1350, (b) 1450, and (c) 1550℃.... 73

Figure 3.24. Electrochemical results and electrical conductivity of 3YSZ and 8YSZ. (a) EIS spectra comparison of electrolyte films with free-standing thickness. (b) Arrhenius plot of total conductivity determined by the 4-probe method. 74

Figure 3.25. Arrhenius plot of total conductivity obtained from the EIS measurement. 75

Figure 3.26. Characteristics of the 3YSZ electrolytes based on sintering temperature (1350-1550℃). Bending strength is for ~90 μm thick specimens at room temperature. Conductivity and ohmic... 78

Figure 3.27. Photograph of 3YSZ and 8YSZ thin sheet (area of 8 x 8 cm², thickness of~11 μm). (a) The flexible 3YSZ film endured severe deformation, such as bending and folding, but (b) the... 79

Figure 3.28. Schematic of fabrication of flexible SOFCs and photographs of the flexible single cell. 80

Figure 3.29. (a) Electrochemical performance and (b) EIS spectra of Ni-8YSZ|3YSZ|LSM- 8YSZ single cell. (c) Photograph of the flexible single cell bending toward anode side and SEM image... 84

Figure 3.30. SEM images of the surface of each electrode of HF-SOFC after bending. 85

Figure 4.1. Electrical conductivity of fluorite oxide. 88

Figure 4.2. Schematic illustration of research objectives. 89

Figure 4.3. Schematic diagram for the preparation of electrolyte materials based on the sol-gel process. 91

Figure 4.4. Photographs the process of solgel synthesis. a) clear sol with a pH of 7, b) xerogel at 250℃, c) process of self-combustion of gel at 300℃, c) black powder after self-combustion, e)... 93

Figure 4.5. TGA-DSC curves of as-synthesized 5Sc powder. 96

Figure 4.6. XRD patterns of 5Sc samples heat treated at (a) 400℃ and (b) 700℃. 97

Figure 4.7. SEM images of as-synthesized 5Sc powder after combustion at 400℃. 99

Figure 4.8. SEM images for comparison of (a, b) the powder shape after calcination at 700℃ and (c-f) the cross section of prepared samples sintered at 1400℃ according to milling or not. 100

Figure 4.9. Phase diagram of the system ZrO₂-Sc₂O₃. 104

Figure 4.10. XRD patterns of x mol% of Sc₂O₃ stabilized zirconia sintered at 900-1500℃ for 3h (x＝(a) 3, (b) 5, (c) 7 and (d) 9). 105

Figure 4.11. XRD patterns of x mol% of Sc₂O₃ stabilized zirconia sintered at 900℃ (x＝3, 5, 7, 9). 106

Figure 4.12. Raman spectra of x mol% of Sc₂O₃ stabilized zirconia (x＝3, 5, 7, 9). 107

Figure 4.13. XRD patterns of x mol% of Sc₂O₃ stabilized zirconia sintered at 1400℃ (x＝(a) 3, (b) 5, 7, 9). XRD pattern of ZrO₂was used to compare with 3Sc. 110

Figure 4.14. (a) XRD patterns and (b) crystallite size of 4Sc1Yb/4Sc1Er/5Sc sintered at 1400℃ for 6h. 114

Figure 4.15. Refined XRD patterns of (a) 5Sc, (b) 4Sc1Er, and (c) 4Sc1Yb sintered at 1400℃ for 6h. 115

Figure 4.16. Variation of lattice parameters and tetragonality as a function of composition of scandia stabilized zirconia. Samples were sintered at 1400℃ for 6h. 117

Figure 4.17. (a) XRD patterns and (b) enlarged main peaks of 4Sc1Yb/4Sc1Er/5Sc sintered at 1500℃ for 6h. 118

Figure 4.18. (a) Photograph of the 5Sc electrolyte film when bent. SEM images of (b, c) the cross section and (d) surface of 5Sc electrolyte sintered at 1400℃. 120