Title Page
Contents
ABSTRACT 12
Ⅰ. General Introduction 15
Ⅱ. Computational Atomic-scale Design and Experimental Verification for Layered Double Hydroxide as an Efficient Alkaline Oxygen Evolution Reaction Catalyst 17
1. Introduction 17
2. Results and discussion 18
2.1. Reaction Free Energy Diagrams of Alkaline OER for Unary, Binary, and Ternary Compounds 18
2.2. Characterization of Structural and Electronic Properties of Ni–Fe–Co Ternary Compounds 28
2.3. Electro-catalytic Properties of Ni–Fe–Co LDH for Alkaline OER 32
3. Methods 37
3.1. DFT Calculations 37
3.2. Catalyst Synthesis 38
3.3. Materials Characterization 39
3.4. Electrochemical Characterization 39
4. Conclusion 41
Ⅲ. Sulfur-Incorporated Nickel-Iron Layered Double Hydroxides for Effective Oxygen Evolution Reaction in Seawater 42
1. Introduction 42
2. Materials and methods 43
2.1. Chemicals 43
2.2. Catalyst synthesis 43
2.3. Electrochemical measurements 45
2.4. Characterizations 45
3. Results and discussion 46
4. Conclusions 56
Ⅳ. Low-iridium doped single-crystalline hydrogenated titanates (H₂Ti₃O₇) with large exposed {100} facets for enhanced oxygen evolution reaction under acidic conditions 57
1. Introduction 57
2. Methods 59
2.1. Chemicals 59
2.2. Synthesis of HTO nanobelts 59
2.3. Synthesis of Ir–HTO nanobelts 59
2.4. Synthesis of Ir-TiO₂ nanobelts 59
2.5. Material characterization 60
2.6. Catalyst ink preparation 60
2.7. Electrochemical measurements 60
2.8. Electrochemical analysis of the intrinsic catalytic activity 61
3. Results and discussion 62
4. Conclusions 70
References 71
Appendix 86
Abstract (in Korean) 101
Table 1. Summary of overpotential and RDS for the simulated LDH models in this study. 29
Fig. 1-1. Atomic-scale geometric structure and OER adsorption energies from DFT calculations on unary Ni(OH)₂ under alkaline OER conditions. 19
Fig. 1-2. Atomic-scale geometric structure and OER adsorption energies from DFT calculations on binary NiFe-LDH under alkaline OER conditions. 20
Fig. 1-3. Atomic-scale geometric structure and OER adsorption energies from DFT calculations on binary NiAl-LDH under alkaline OER conditions. 21
Fig. 1-4. Atomic-scale geometric structure and OER adsorption energies from DFT calculations on binary NiCo-LDH under alkaline OER conditions. 22
Fig. 1-5. Atomic-scale geometric structure and OER adsorption energies from DFT calculations on ternary NiFeAl-LDH under alkaline OER conditions. 23
Fig. 1-6. Atomic-scale geometric structure and OER adsorption energies from DFT calculations on ternary NiAlCo-LDH under alkaline OER conditions. 25
Fig. 1-7. Atomic-scale geometric structure and OER adsorption energies from DFT calculations on ternary NiFeCo-LDH under alkaline OER conditions. 26
Fig. 1-8. Comparison of overpotentials of Ni-Fe-Co-Al based unary, binary, and ternary LDHs for alkaline OER. 28
Fig. 1-9. a) SEM images and the corresponding b) EDS mapping results of NiFeCo-LDH. c) Quantitative elemental analysis in NiFeCo-LDH from... 30
Fig. 1-10. a-c) TEM images and d-f) HR-TEM images of NiFeCo-LDH. g-i) Inverse FFT images processed from the HR-TEM images in the insets of... 31
Fig. 1-11. a) LSV curves and b) Tafel slopes of NiFe-LDH, NiFeCo-LDH, and IrO2 measured in 1 M KOH using scan rate of 5 mV s⁻¹. c) ECSA... 33
Fig. 1-12. a-b) TEM images of NiFeCo-LDH after continuous CP measurement for 72 hrs under 100 mA cm⁻² in 1 M KOH. The inset shows... 35
Fig. 2-1. Scanning electron microscopy (SEM) images of (a-c) Ni-LDH, (d-f) NiFe-LDH, and (g-i) NiFe-LDH-S350. (j) X-ray diffraction (XRD)... 46
Fig. 2-2. (a-b) Transmission electron microscopy (TEM) and (c) high-resolution transmission electron microscopy (HR-TEM) images of... 46
Fig. 2-3. X-ray photoelectron spectroscopy (XPS) spectra of (a) Ni, (b) Fe, (c) O, and (S) in NiFe-LDH-S350. 48
Fig. 2-4. (a) Linear sweep voltammetry (LSV) curves for Ni-LDH, NiFe-LDH, NiFe-LDH-S350 measured in an electrolyte containing 1.0 M KOH... 49
Fig. 2-5. (a) Turn over frequencies, (b) activation energies, (c) Cdl, and (d) ECS- normalized LSV curves of Ni-LDH, NiFe-LDH, and NiFe-LDH-S350... 52
Fig. 2-6. Chronopotentiometry measurements at 100 mA cm⁻² for NiFe-LDH and NiFe-LDH-S350 in an electrolyte containing 1.0 M KOH and... 54
Fig. 2-7. (a-b) Transmission electron microscopy (TEM) and (c) high-resolution transmission electron microscopy (HR-TEM) images of... 55
Fig. 2-8. X-ray photoelectron spectroscopy (XPS) spectra of (a) Ni, (b) Fe, and (c) S for NiFe-LDH-S350 after 12 h of chronopotentiometry at... 56
Fig. 3-1. (a) Schematic illustration of the Ir-HTO preparation process. Scanning electron microscopy (SEM) images of (b-c) HTO, (d-e) Ir-HTO. (f)... 62
Fig. 3-2. (a-d) HR-TEM images of Ir-HTO. (e-i) EDS mapping images of Ir-HTO for Ti, Ir and O elements. (j) EDS line scan of Ir-HTO for Ti, Ir... 64
Fig. 3-3. (a) Linear sweep voltammetry (LSV) curves for HTO, Ir-TiO₂, Ir-HTO and IrO₂ measured in an electrolyte containing 0.1M HClO₄, and... 65
Fig. 3-4. (a) Comparison of overpotentials required to achieve current densities of 10 mA cm⁻² for OER and corresponding Tafel slopes in... 66
Fig. 3-5. (a-c) HR-TEM images, (d-h) EDS mapping images for Ti, Ir, O and mearged elements, XPS spectra of (j) Ti, (k) Ir and (l) for Ir-HTO... 66