Redox behavior of some selected metals in room temperature ionic liquids = 상온 이온성 액체에서 선택된 금속들의 산화/환원 거동에 대한 연구

다국어 초록 (Multilingual Abstract)

Room temperature ionic liquid (RTIL) is a salt, consisting of large asymmetric cation and complex anion, which is stable in liquid phase below 100°C. Properties of RTILs are solely dependent on their constituent cation and anion. In terms of electrochemistry, the most significant properties of RTILs that should be considered are viscosity, conductivity, and electrochemical stability window. Electrochemical stability window, which refers to a potential range where cation and anion are neither reduced nor oxidized, of RTILs is typically wider than aqueous electrolytes. This feature enables electrodeposition of metals with large negative reduction potential such as aluminum, zinc, magnesium, and lithium, which are otherwise unable to be recovered in aqueous solvents. In battery application, replacing conventional organic solvents with nonvolatile and nonflammable RTILs would help to improve battery safety.
This dissertation focuses on the electrochemical reactions of metal electrodes in RTILs, including electrodeposition and corrosion. Three different topics regarding the oxidation and reduction reactions of some selected metals in RTILs are discussed in this dissertation. The effect of RTIL structures on the electrodeposition/dissolution behavior of lithium is investigated in the first topic. The second topic is about the oxidation and reduction reversibility of zinc anode and the effect of water addition in RTIL-based zinc-air battery application. In the third topic, the corrosion susceptibility of some selected metals is evaluated in a protic RTIL containing available proton on cation, and compared with aprotic one with a similar structure.
RTIL structure is confirmed to affect the electrodeposition/dissolution potential of lithium. The largest portion of lithium metal in deposits is obtained from a sample electrodeposited in RTIL with the widest electrochemical stability window, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMPyr] [NTf2]). In regard to the application of RTILs as an electrolyte for zinc-air battery, zinc electrode shows reversible oxidation-reduction reactions in [BMPyr] [NTf2]. However, the presence of water gives a significant effect on the redox reactions of zinc electrode. Protic RTIL (1-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide) is confirmed to show a narrower electrochemical stability window compared to that of aprotic RTIL ([BMPyr] [NTf2]) of similar structure and is more reactive towards metals. Lower corrosion potentials and higher corrosion current densities are observed in the protic RTIL.

목차 (Table of Contents)

• Chapter 1 Introduction 1
• 1.1 Definition and classifications of room temperature ionic liquids 1
• 1.2 Electrochemical properties of RTILs 6
• 1.3 Electrochemical applications of RTILs 8
• 1.4 Corrosion behavior of metallic materials in RTILs 9
• 1.4.1 Corrosion mechanism in RTILs 9
• 1.4.2 Overview of metal/alloy corrosion in RTILs 12
• 1.5 Scope of dissertation 21
• Chapter 2 Experimental Methods 23
• 2.1 Cell assembly 23
• 2.2 Reference electrode 25
• 2.3 Cyclic voltammetry 30
• 2.4 Potentiodynamic anodic polarization 30
• 2.5 Electrochemical Impedance Spectroscopy 31
• Chapter 3 Effects of Room Temperature Ionic Liquid Structures on Electrochemical Behavior of Lithium 33
• 3.1 Introduction 33
• 3.2 Experimental 36
• 3.3 Results and discussion 40
• 3.3.1 Effect of cation structure on cathodic stability of RTILs 40
• 3.3.2 Effect of cation structure on lithium redox behavior 44
• 3.3.3 Effect of anion structure on lithium redox behavior 56
• 3.4 Conclusions 60
• Chapter 4 Effect of Water on the Stability of Zinc Electrodes in RTIL-based Metal-Air Battery Application 63
• 4.1 Introduction 63
• 4.1.1 Introduction to metal-air battery 63
• 4.1.2 RTILs as electrolytes for Zn-air battery 69
• 4.2 Experimental 72
• 4.3 Results and discussion 74
• 4.4 Conclusions 95
• Chapter 5 Corrosion Behavior of Metals in Protic RTILs 98
• 5.1 Introduction to protic RTILs 98
• 5.2 Experimental 101
• 5.3 Results and discussion 103
• 5.4 Conclusions 114
• Chapter 6 Conclusions and Future Works 117
• References 121
• Nomenclature 135
• 국문초록 138
• Acknowledgements 142