Aqueous Redox Flow Batteries using Transition Metal Complexes as Redox Active Materials = 전이금속 복합체를 이용한 레독스 흐름전지 개발 및 성능향상에 대한 연구|RISS 상세보기

다국어 초록 (Multilingual Abstract)

In this study, redox materials using low-cost transition metals and ligands were synthesized to replace vanadium and the optimization and performance evaluation were conducted to apply these materials for redox flow battery. The triethanolamine (TEA), triisopropanolamine (TiPA), and 3-[Bis(2-hydroxyethyl)amino
]-2-hydroxypropanesulfonic acid (DIPSO) are used as ligands, which are amino alcohol-based ligands, have the characteristic of strongly bonding with transition metals in a basic environment. Furthermore, since redox reactivity is exhibited in the range of -1.1 to –1.03 V (vs. Ag/AgCl) and -0.14 to –0.07 V (vs. Ag/AgCl) in the aqueous system when bonded with iron (Fe) and cobalt (Co), respectively, it could be used as an active material for the anode and a cathode active material of a redox flow battery having an open-circuit voltage (OCV) of about 0.95 V.
The Fe-L (L: TEA, TiPA, DIPSO)-based complex had a side reaction where iron ions were separated from the complex and reduced to a metal form on the electrode surface when the redox reaction was repeated. To solve this problem, an excessive amount of ligand could be added to the supporting electrolyte to solve it, but the viscosity of the electrolyte also increased, so did the resistance of the electrolyte. Therefore, a Fe(DIPSO) complex which may be stably used as a redox active material was developed by modifying a ligand to increase a stability constant of the complex and setting a charge limit condition of a battery by grasping a potential at which metal is electrochemically reduced.
The Co-L (L: TEA, TiPA, DIPSO)-based complexes were chemically precipitated when exposed to supporting electrolytes with strong base properties for a long period of time. In order to solve this problem, a method of adding an excessive amount of ligand may not be used due to the oxidation reaction of the ligand itself, and only a method of increasing a stability constant of the complex by modifying the ligand may be used. Therefore, Co(TiPA) has been developed as the most stable complex that can be used as a redox active material.
When the redox flow battery was driven with this Fe(DIPSO) and Co(TiPA), it was possible to develop a stable Fe(DIPSO)/Co(TiPA) RFB with a high energy efficiency of 61.1%, a capacity retention rate of 88% or more for 289 hours.

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국문 초록 (Abstract)

본 연구에서는 바나듐이 아닌 저가의 전이금속과 리간드를 활용한 레독스 물질을 합성하고 이를 레독스 흐름전지에 적용하기 위해 필요한 최적화 및 성능평가를 진행하였다. 사용된 리간드는 아미노알콜계열의 리간드인 Triethanolamine (TEA), Triisopropanolamine (TiPA), and 3-[Bis(2-hydroxyethyl)amino]-2-hydroxypro-
panesulfonic acid (DIPSO) 이며, 이들은 염기성 환경에서 전이금속과 강하게 결합하는 특징을 가지고 있다. 또한, 철 (Fe) 그리고 코발트 (Co) 와 결합했을 때 수계에서 각각 -1.1 to –1.03 V (vs. Ag/AgCl) 그리고 -0.14 to –0.07 V (vs. Ag/AgCl)의 범위에서 레독스 반응성을 나타내기 때문에, 약 0.95V의 기전력을 가지는 레독스 흐름전지의 음극과 양극의 활물질로써 사용될 수 있었다.
Fe-L(L: TEA, TiPA, DIPSO)계열의 복합체는 레독스 반응을 반복하면 철 이온이 복합체로부터 이탈하여 전극 표면에 금속형태로 환원되는 부반응이 있었다. 이를 해결하기 위해서는 과량의 리간드를 보조전해질에 추가하여 해결할 수 있었지만 전해질의 점도도 같이 증가하기 때문에 전해질의 저항도 같이 증가하는 문제가 수반되었다. 따라서 리간드를 개질하여 복합체의 안정성 상수를 직접적으로 증가시킴과 동시에 전기화학적으로 금속이 환원되는 전위를 파악하고 전지의 충전 한계조건을 설정하여, 안정적인 레독스 활물질로 사용할 수 있는 Fe(DIPSO) 복합체를 개발할 수 있었다.
Co-L(L: TEA, TiPA, DIPSO)계열의 복합체는 강염기 성질의 보조전해질에 장기간 동안 노출시켰을 때, 화학적으로 침전되는 것을 확인하였다. 이를 해결하기 위해 과량의 리간드를 추가하는 방법은 리간드 자체의 산화반응이 있어 사용할 수 없었고, 리간드를 개질하여 복합체의 안정성 상수를 증가시키는 방법만 사용할 수 있었다. 결과적으로, 안정적으로 레독스 활물질로 사용할 수 있는 복합체인 Co(TiPA)를 개발할 수 있었다.
이 Fe(DIPSO)와 Co(TiPA)를 가지고 레독스 흐름전지를 구동했을 때, 61.1%의 높은 에너지효율을 가지며, 289시간동안 88%이상의 용량유지율을 보이며 안정적으로 구동하는 Fe(DIPSO)/Co(TiPA) RFB를 개발할 수 있었다.

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본 연구에서는 바나듐이 아닌 저가의 전이금속과 리간드를 활용한 레독스 물질을 합성하고 이를 레독스 흐름전지에 적용하기 위해 필요한 최적화 및 성능평가를 진행하였다. 사용된 리간드...

목차 (Table of Contents)

Summary i
List of table iii
List of figures vi
Chapter I. Overall Introduction 1

Summary i
List of table iii
List of figures vi
Chapter I. Overall Introduction 1
1. Research background 2
2. Research purpose 4
5. Reference 6
Chapter II. Theoretical Background 9
1. Redox flow battery 10
2. Metal-ligand complex 13
3. Thermodynamics and Electrochemistry 15
4. Spectroscopic analysis 17
5. Reference 18
Chapter III. Metal-organic redox flow batteries using Iron triethanolamine and cobalt triethanolamine complexes 20
1. Introduction 21
2. Experimental 24
2.1 Materials 24
2.2 Preparation of Co and Fe complex synthesized with TEA ligand 24
2.3 Electrochemical evaluations 24
2.4 Chemical characterizations 25
3. Results and discussion 26
3.1 Optimization of active species consisting of the metal-organic complex for AMORFB 26
3.2 Optimization of the alkaline concentration for Co(TEA) complex 35
3.3 Electrochemical behaviour and viscosity of electrolytes containing Co(TEA) and Fe(TEA) 40
3.4 Performance and cost of AMORFB using Co(TEA) and Fe(TEA) redox couple 46
4. Conclusion 50
5. References 51
Chapter IV. Highly stable aqueous metal-organic redox flow batteries using cobalt triisopropanolamine and iron triisopropanolamine complexes 55
1. Introduction 56
2. Experimental 58
2.1 Materials 58
2.2 Preparation of Co and Fe complex synthesized with TEA or TiPA ligand 58
2.3 Viscosity measurement 59
2.3 Evaluations of the electrochemical properties of metal-ligand complexes 59
2.4 Solubility measurement of metal-ligand complexes using UV-VIS spectrometer 59
2.5 Evaluations of the electrochemical properties of metal-ligand complexes 59
2.6 Analysis of the surface of carbon felt using SEM-EDS 60
3. Results and discussion 62
3.1 Electrochemical evaluations of Co(TiPA) and Fe(TiPA) complexes 62
3.2 Solubility measurements of Co(TiPA) and Fe(TiPA) complexes 72
3.3 The performances of RFB full using Co(TiPA) and Fe(TiPA) complexes 75
4. Conclusion 86
5. Reference 87
Chapter V. Optimization of iron and cobalt based metal-organic redox couples for long-term stable operation of aqueous metal-organic redox flow batteries 91
1. Introduction 92
2. Experimental 94
2.1 Materials 94
2.2 Preparation of Co and Fe complex synthesized with TiPA or DIPSOligand 94
2.3 Evaluations of the electrochemical properties of metal-ligand complexes 95
2.4 Analysis of the surface of carbon felt suing SEM-EDS 96
3. Results and discussion 98
3.1 Electrochemical evaluations of Co complexes 98
3.2 Electrochemical evaluations of Fe complexes 101
3.3 Fe core ion reduction of Fe complexes 103
3.4 The performance evaluations of AMORFB full cells 109
4. Conclusion 124
5. Reference 125
Chapter VI. Overall Conclusion 130
국문초록 133

참고문헌 (Reference)

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