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Development of Advanced Electrodes for High Temperature Solid-state Energy Conversion Devices

Development of Advanced Electrodes for High Temperature Solid-state Energy Conversion Devices
Kim, Kyeong Joon
DGIST Authors
Kim, Kyeong JoonLee, HochunLee, Kang Ta다
Lee, Kang Ta다
Issued Date
Awarded Date
Solid oxide cells, High temperature catalyst, Composite electrode, Active and stable
Solid oxide cells (SOCs) are powerful electrochemical devices for sufficient and simultaneous produc-tion and storage of eco-friendly energy. The SOCs can operate reversibly in a solid oxide fuel cell (SOFC) mode to generate electricity from chemical fuels, and a solid oxide electrolysis cell (SOEC) mode to convert electrical power into chemical fuels. An SOC is composed of high-density electrolyte, oxygen electrode, and fuel electrode. During operation, the oxygen electrode provides an active site for oxygen reduction or evolu-tion reaction (ORR / OER), while the fuel electrode oxidizes fuel (e.g. H2, CH4 and CO) or produces fuel (e.g., electrolysis of H2O and CO2). Both electrodes must provide a sufficient number of active sites for electrode reactions as well as suitable routes for rapidly transporting species (ions, electrons, and gas molecules, etc.) involved in the continuous electrode reaction. Thus, both electrodes are essential to improve SOC perfor-mance and stability. Currently, nickel/yttria-stabilized zirconia (Ni–YSZ) has been the most widely used fuel electrode material for SOCs due to its high catalytic activity, operational reliability, and acceptable cost. However, the long-term durability of Ni–YSZ is inadequate due to inherent redox instability and severe car-bon deposition during operation. To address this, alternatives to Ni-YSZ electrode materials, including various perovskite oxides, have been developed and investigated, many of which have shown significant catalytic activity and stability. Owing to their superior redox-stability, lanthanum titanium-based perovskite oxides have garnered significant interest as a promising reliable ceramic fuel electrode for SOFCs. Moreover, recent studies demonstrated that A-site deficiency of La-doped SrTiO3 perovskite could effectively and simultane-ously promote conductivity and catalytic activity. Among those, a La0.4Sr0.4TiO3−δ (LST44) material in the LaxSr1−3x/2TiO3−δ series is a promising candidate as a ceramic fuel electrode due to its redox tolerance and phase stability. Therefore, LST44-Ce0.9Gd0.1O1.95 (GDC) composite fuel electrodes were developed, and their electrochemical performance and stability were investigated. (Chapter III) To improve the electrochemical performance, La2NiO4+δ with a Ruddlesden-Popper structure (RP structure, space group I4/mmm or F4/mmm) has been intensively studied for its rapid surface exchange reaction and bulk ion diffusion. In its crystal structure, perovskite (ABO3) and rock salt (AO) layers are alternately stacked along the c-axis. Intersti-tial oxygen is preferentially localized at the pseudo-tetrahedron of La in the rock salt, and has fast ionic con-duction paths through the AO layers, promoting ionic and electronic conductivity. Furthermore, Gd and Mn co-doped layered perovskite fuel electrode materials can be rationally designed in order to promote the elec-trocatalytic activity, mixed conductivity, and high stability. Therefore, we developed novel SrGdNixMn1-xO4±δ (x = 0.2, 0.5, 0.8) materials with a Ruddlesden-Popper structure and used them as SOFC fuel electrodes. (Chapter IV)
Meanwhile, practical applications for SOC systems have been limited due to chemical reactivity of ox-ygen electrode with adjacent SOC components, resulting in poor long-term stability of SOCs. As an alterna-tive, due to their high electrical conductivity and good chemical compatibility with SOFC components, some AB2O4-type spinel materials, which are widely used as protective coating layers on metallic interconnects, have been recently investigated as oxygen electrode materials for IT (intermediate temperature)-SOFCs. Therefore, we developed a novel spinel oxygen electrode material of Cu-doped Mn1.5Co1.5O4. The electro-chemical performance of an SOFC with the MCCO-(Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 (ScSZ) composite oxygen electrode was evaluated to demonstrate the feasibility of using the MCCO materials as ORR catalysts for IT-SOFCs. (Chapter V) Moreover, due to sluggish ORR/OER activities at IT region, the development of oxygen electrodes with high catalytic activity and stability is essential for high performance SOCs. For example, Sr-doped LaMnO3 (LSM), which is commonly used for SOC oxygen electrode, lacks ionic conductivity and pos-sesses a highly thermal-activated nature for oxygen reduction/evolution reaction. To overcome this limita-tion, conventional oxygen ion-conducting phase, such as Gd-doped CeO2 (GDC) and Y2O3-stabilized ZrO2 (YSZ), have been combined with LSM, resulting in reduced resistance of SOC electrode. Owing to their excep-tionally high ionic conductivity, Bi2O3-based oxide ion conductors are promising materials for replacing con-ventional oxide ion conductors such as YSZ and GDC. Particularly, Dy and Y co-doped Bi2O3 (DYSB) with low total dopant concentration (12 mol%) required for cubic phase stabilization showed extremely high con-ductivity at IT region. In this study, the electrochemical properties of LSM combined with DYSB (LSM-DYSB) were investigated in SOFC, SOEC, and reversible SOC operating conditions to explore its advantage as oxygen electrode. Finally, we succeeded in achieving great performance and stability in SOC. (Chapter VI) This systematic study suggests a method for rational design of advanced alternative electrodes for applica-tion in SOC.
Table Of Contents
Ⅰ. Introduction
1.1 Motivation 1
1.2 Objectives and Overview 2

ⅠI. Background
2.1 Solid Oxide Cells (SOCs) 6
2.1.1 Solid Oxide Fuel Cells (SOFCs) 6
2.1.2 Solid Oxide Electrolysis Cells (SOECs) 7
2.2 Oxide ion conductors for SOCs 8
2.2.1 ZrO2-based oxide ion conductors 9
2.2.2 CeO2-based oxide ion conductors 10
2.2.3 Bi2O3-based oxide ion conductors 11
2.2.3 LaGaO3-based oxide ion conductors 11
2.3 Fuel electrodes for SOCs 12
2.3.1 LST-based electrodes 13 A-site deficient LST materials 14
2.3.2 Ruddlesden popper (RP) phase-based fuel electrodes 15
2.4 Oxygen electrodes for SOCs 16
2.4.1 Perovskite-based oxygen Electrodes 17
2.4.2 Spinel-based oxygen Electrodes 18

ⅠII. Redox tolerant and highly stable LST-based fuel electrode
3.1 Introduction 30
3.2 Experimental procedure 31
3.2.1 Material preparation 31
3.2.2 SOC fabrication 32
3.2.3 Characterization 32
3.3 Result and discussion 33
3.3.1 Phase analysis 33
3.3.2 Electrochemical performance 35
3.4 Conclusion 38

ⅠV. High performance SGNM fuel electrode induced by Ni nanoparticle exsolution
4.1 Introduction 44
4.2 Experimental procedure 45
4.2.1 Material preparation 45
4.2.2 SOC fabrication 46
4.2.3 Characterization 46
4.3 Result and discussion 48
4.3.1 Phase analysis 48
4.3.2 XPS analysis 50
4.3.3 H2-TPR analysis 53
4.3.4 Electrochemical performance 54
4.4 Conclusion 59

V. Novel spinel-based oxygen electrode
5.1 Introduction 77
5.2 Experimental procedure 79
5.2.1 Material preparation 79
5.2.2 SOC fabrication 79
5.2.3 Characterization 80
5.3 Result and discussion 80
5.3.1 Phase analysis 81
5.3.2 Electrochemical performance 82
5.4 Conclusion 83

VI. Highly active and stable Bi-oxide based oxygen electrode
6.1 Introduction 91
6.2 Experimental procedure 93
6.2.1 Material preparation 93
6.2.2 Symmetrical cell fabrication 93
6.2.3 SOC fabrication 94
6.2.4 Characterization 94
6.3 Result and discussion 95
6.3.1 Powder characterization 95
6.3.2 Electrochemical performance 96
6.4 Conclusion 98
Department of Energy Science and Engineering
Related Researcher
  • 이호춘 Lee, Hochun 에너지공학과
  • Research Interests Lithium-ion batteries; Novel Materials for rechargeable batteries; Novel energy conversion;storage systems; Electrochemistry; 리튬이차전지; 이차전지용 신규 전극 및 전해액; 신규 에너지변환 및 저장 시스템; 전기화학
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