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Study of Anode Supported GDC/YSZ Bi-layered Electrolyte Solid Oxide Fuel Cell via Cold Press Process : 콜드 프레스 공정을 이용한 음극지지체 GDC/YSZ 전해질 이중층 고체산화물 연료전지 연구
| DC Field | Value | Language |
|---|---|---|
| dc.contributor.advisor | 차석원 | - |
| dc.contributor.author | 최훈 | - |
| dc.date.accessioned | 2017-07-13T06:12:20Z | - |
| dc.date.available | 2017-07-13T06:12:20Z | - |
| dc.date.issued | 2014-02 | - |
| dc.identifier.other | 000000016813 | - |
| dc.identifier.uri | https://hdl.handle.net/10371/118352 | - |
| dc.description | 학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2014. 2. 차석원. | - |
| dc.description.abstract | The fact that hydrogen will be the last energy source became no more attractive to us. The main issue is which kind of energy conversion device will be going to survive in the future. Since many researchers highlighted the fuel cell as the next generation power source, a lot of researched have been conducted to commercialize it.
SOFCs have many advantages in comparison with typical PEMFCs which have shown water management problem, usage of novel catalyst, patent issue for polymer electrolyte, expansive graphite bipolar plate and CO poisoning. So many researchers in energy field have been thought SOFC would be the promising device. But the main bottle neck for the commercialization of SOFC has been its high operation temperature. It can cause thermal mismatch between MEA, nickel agglomeration, reactions between component materials, restricted sealant choice and expensive interconnecter material. So we focused our interest to IT-SOFC. Its temperature position can avoid many problems of HTSOFC and LT-SOFC maintaining the competitiveness of original SOFCs characteristics. Moreover, process cost issue about compaction, sintering and more complicated high temperature process is one of the bottle-neck for commercialization. In this study, we studied the lower the operating temperature in order to solve these problems, while reducing the thickness of the electrolyte and dropping the number of steps compared to the conventional method. First, we prepared the bi-layer electrolyte solid oxide fuel cell which was deposited yttria-stabilized zirconia (YSZ) and gadolinia dopted ceria (GDC) which is high ionic conductivity material at low and intermediate temperature. This structure is verified that high performance, sufficient durability and operation in a low temperature. It is confirmed the successful deposition of YSZ through the scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). We obtained a 50% improvement power density and 5% higher open circuit voltage (OCV) than the output of pure GDC electrolyte cell at 600 degrees Celsius. We confirmed that the YSZ layer prevent enhancing electronic conductivity and micro crack which can make voltage-drop and enlarge ohmic loss in order to reduce GDC layer by SEM image and EIS. Second, because we verified effect of YSZ/GDC bi-layer electrolyte structure to the performance, it is studied about bi-layer electrolyte anode supported type solid oxide fuel cell structure which could have higher power density. Various wet ceramic processes and thin film deposition processes are employed to electrolyte deposition method to calcined anode substrate. Finally, we established cold press process that can sinter from substrate to electrolyte at one step process. In order to enhance the controllability and uniformity of thickness of the layer, spray dry coating method that can control about micron range using powder vehicle is employed. The compressed dry powder substrate-bi-layer electrolyte was co-sintered, and we fabricated LSCF-GDC cathode using screen printing method. It is possible as compared with the wet method, to reduce the sintering step one or more times, forming method such a great advantage in time and cost. We obtained power density of 210mW/cm2 at 600 degrees Celsius, and 409mW/cm2 at 800 degrees Celsius from prepared bi-layer electrolyte cell. It is 0.1V higher open circuit voltage and 15% higher maximum power density rather than one of non bi-layer electrolyte cell. Third, we have improved the fabrication process to increase the performance of bi-layer electrolyte cell via cold press process. In order to make porous anode substrate, the PMMA powder was mixed with anode substrate powder which is used previous bi-layer electrolyte cell fabrication. And it is achieved the power density is 460mW/cm2 at 700 degrees Celsius. Further, by adding one functional layer between the anode substrate and electrolyte layer, to complement the reduction in mechanical strength that can occur in the case of porous anode support, to improve the electrochemical performance by cold press process. As a result, it was possible to obtain a power density and mechanical strength is enhanced, and is more stably maintained even during operation. Finally, we modeled and calculated the compaction behavior during cold press process using COMSOL multiphysics. The Surface von Mise stress was predicted using the Drucker-Prager Cap model. Through this model, we were able to determine at the time of production to minimize the damage, and the condition of the powder. In addition, through the modeling, the basic direction for the production of large-scale cells could be present. | - |
| dc.description.tableofcontents | Chapter 1. Introduction 1
1.1 Research Background………………………………………….…………….1 1.2 Solid oxide fuel cell ………………………...………………….……………5 1.3 The operating temperature of SOFCs…………………………….………….8 1.3.1 Reducing the thickness of electrolyte……………………………………11 1.3.2 High conductivity electrolytes material…………………………………12 1.4 Bi-layered electrolytes SOFCs………………………………….…………..14 1.5 The supported type of SOFC………………………………….…………….19 Chapter 2. Cell fabrication and experimental process 22 2.1 Cell fabrication and test for verification of YSZ-GDC bi-layer……….……22 2.1.1 The components of bi-layered electrolyte………………………….…...24 2.1.2 ALD-YSZ for a functional layer………………………………….…….25 2.1.3 Cell fabrication…………………………………………………….……27 2.1.4 Cell test procedure……………………………………………….……..30 2.1.5 Result of ALD-YSZ/GDC bil-layered cell test………………….……...38 2.2 Approach of various anode-supported type SOFC cell fabrication process ...………………………………………………………………………….48 2.2.1 Literature survey………………………………………………….…….49 2.2.3 Cold press process………………………………………………….…..52 2.2.4 Summary of cell fabrication process and Cell test procedure …………54 Chapter 3. Test of the YSZ/GDC bi-layered electrolyte anode supported type cell via cold press process 63 3.1 Introduction………………………………………….………………………63 3.1.1 Literature survey………………………………….…………………….64 3.2 Research Methodology…………………………..………………………….65 3.3 Results…………………………………………..………….………………..69 3.4 Conclusion………………………………………………….……………….75 Chapter 4. Anode functional layer for porous anode substrate 76 4.1 Introduction…………………………………………………………………76 4.2 Porous anode substrate cell……………………………………..………..….77 4.2.1 Porous anode substrate cell fabrication…………………….….……..…77 4.2.1 Cell fabrication……………………………………………….…………78 4.2.2 Cell test result………………………………………….……………….79 4.3 Anode functional layer cell……………………………………….…………82 4.3.1 Fabrication…………………………………………………….………..82 4.3.2 Experimental…………………………………………………..………..85 4.3.3 Result………………………………………………………..……….…86 4.3.4 Discussion……………………………………………………..………..91 Chapter 5. Numerical analysis of behavior of fabrication process by finite element method 93 5.1 Introduction……………………………………………………….…………93 5.2 Geometric description…………………………………………….…………94 5.3 Model description……………………………………………….…………..96 5.4 Analysis result………………………………………………………………98 Chapter 6. Concluding remarks 102 6.1 Conclusion………………………………………………………………...102 6.2 Future works………………………………………………………………105 List of figures Fig 1.1 Operation principle of a fuel cell [1] 4 Fig 1.2 Schematics of PEMFC, MCFC and SOFC [5] 7 Fig 1.3 Advantages of SOFCs 7 Fig 1.4 Competitiveness of IT-SOFCs 10 Fig 1.5 Comparison of conductivity of various materials 13 Fig 1.6 The various approaches about bi-layer cell fabrication process[23,47,75] 18 Fig 1.7 Types of mechanical supported cell. (a) the cathode supported type (b) the electrolyte supported type (c) the anode supported type 21 Fig 2.1 Schematic of a YSZ/GDC bi-layered electrolyte SOFC 23 Fig 2.2 Example of ALD-YSZ based μSOFC [56] 26 Fig 2.3 Schematics of the ALD-YSZ / GDC cell and the pure GDC cell and actual image of the anode and cathode sides 29 Fig 2.4 ALD-YSZ bi-layered cell fabrication procedure 29 Fig 2.5 Button cell test station and P&ID diagram 32 Fig 2.6 Cell pressing unit and indicator 33 Fig 2.7 MFCs and controllers 34 Fig 2.8 Solartron SI 1287 and SI 1260 34 Fig 2.9 Experiment preparation process on the fifth design fixture. 37 Fig 2.10 XPS spectra on the surfaces of ALD-YSZ / GDC samples (red) before the electrode sintering process and (blue) after the cell operation 40 Fig 2.11 XPS depth profile of the bi-layered electrolyte which was 345 cycles (50nm) ALD-YSZ coated GDC 40 Fig 2.12 OCV transitions of the pure GDC cell and of the 690 cycles (100nm) ALD-YSZ / GDC cell at 620°C using 5% H2 fuel during the anode reduction step 42 Fig 2.13 iV and power density curves at 600°C for the pure GDC cell, 50nm ALD-YSZ / GDC cell, and the 100nm ALD-YSZ / GDC cell 45 Fig 2.14 Comparison of the iV and power density at 600°C as the hydrogen and air feed rates increased from 200sccm to 300sccm 45 Fig 2.15 EIS Nyquist spectra at 600°C (a) for the 690 cycles (100nm) ALD-YSZ / GDC cell and (b) for the pure GDC cell 47 Fig 2.16 ALD bi-layered SOFC SEM cross sectional, power and IV performance[39] 51 Fig 2.17 Wet cermic process bi-layered SOFC SEM cross sectional, power and IV performance[47] 51 Fig 2.18 Cold press single layer anode supported SOFC SEM cross sectional image[54] 53 Fig 2.19 Power density and IV curve of Electrolyte supported cell and Anode supported cell. 56 Fig 2.20 IV and power density of spray coated electrolyte cell, 600℃ humidified H2 : 100 SCCM N2 : 100 Air : 100 SCCM 60 Fig 2.21 Cross sectional SEM image of the spray coated electrolyte 60 Fig 2.22 Modified test fixture using gold ring sealant 62 Fig 3.1. (a) Scanning electron microscopy of cross-section of a YSZ/GDC bilayer electrolyte film on a anode substrate. (b) morphology of GDC electrolyte plane 66 Fig 3.2. Measured OCV vs temperature for single cells with 50 µm GDC monolayer electrolyte, 50 µm YSZ monolayer electrolyte, and 8µm YSZ/ 40µm GDC bilayer electrolyte, respectively. 67 Fig 3.3 (a) Cell voltage and (b) power density as function of current density of a YSZ (8 µm)/GDC (40 µm) bilayer electrolyte cell measured between 600 and 800 °C in humidified hydrogen and open air. 71 Fig 3.4. Cell voltage and power density vs. current density of a YSZ (8 µm) / GDC (40 µm) bilayer electrolyte cell measured 600 ◦C in humidified hydrogen and open air. 72 Fig 3.5 Result of electrochemical impedance spectroscopy of GDC single electrolyte cell and YSZ/GDC bilayer electrolyte cell, 600°C 74 Fig 4.1 IV and power density of PMMA porous substrate bi-layer electrolyte cell 80 Fig 4.2 EIS reslut of PMMA porous substrate bi-layer electrolyte cell 81 Fig 4.3 IV performance curve in various thickness of anode functional layer 89 Fig 4.4 Power density in various thickness of anode functional layer 89 Fig 4.5 Similarity of IV curve of dense anode substrate cell and thick anode functional layer cell 90 Fig 4.6 Peak power density of various thickness of anode functional layer 90 Fig 5.1 Schematic diagram of the substrate model 95 Fig 5.2. Drucker-Prager Cap model: yield surface in the p-q plane. 97 Fig 5.3Criterion stress of compaction processed cell 101 Fig 6. 1 Summary of whole test results in this study 104 List of tables Fig 1.1 Various researches about bi-layer cell process 17 Fig 2.1 Summary of fabrication approaches 59 Fig 2.2 The electrolyte slurry recipe for wet ceramic process 59 Fig 4.1 Various approach for fabrication of anode functional layer 84 Fig 4.2 Thickness of Anode functional layer 84 Fig 5.1 Dimension and global parameter of the substrate model 95 Fig 5.2 Properties of materials for FEM modeling 100 | - |
| dc.format | application/pdf | - |
| dc.format.extent | 4304502 bytes | - |
| dc.format.medium | application/pdf | - |
| dc.language.iso | en | - |
| dc.publisher | 서울대학교 대학원 | - |
| dc.subject | solid oxide fuel cell (SOFC) | - |
| dc.subject | intermediate temperature | - |
| dc.subject | gadolinia doped ceria (GDC) | - |
| dc.subject | bi-layered electrolyte | - |
| dc.subject.ddc | 621 | - |
| dc.title | Study of Anode Supported GDC/YSZ Bi-layered Electrolyte Solid Oxide Fuel Cell via Cold Press Process | - |
| dc.title.alternative | 콜드 프레스 공정을 이용한 음극지지체 GDC/YSZ 전해질 이중층 고체산화물 연료전지 연구 | - |
| dc.type | Thesis | - |
| dc.description.degree | Doctor | - |
| dc.citation.pages | 123 | - |
| dc.contributor.affiliation | 공과대학 기계항공공학부 | - |
| dc.date.awarded | 2014-02 | - |
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