Title Page
ABSTRACT
초록
PREFACE
Contents
NOMENCLATURE 26
CHAPTER 1. INTRODUCTION 28
1.1. Global warming and greenhouse gases 28
1.2. Carbon neutrality and electrochemical CO₂ reduction reaction (e-CO₂RR) 32
1.3. Basic principle of electrochemical CO₂ reduction reaction (e-CO₂RR) 36
1.3.1. Thermodynamics of e-CO₂RR 36
1.3.2. e-CO₂RR mechanism 39
1.3.3. The electrochemical CO₂ to CO conversion and hydrogen evolution reaction (HER) mechanism 42
1.4. Oxygen evolution reaction (OER) mechanism at anode 44
1.5. Type of CO₂RR electrolyzers 47
CHAPTER 2. Experimental Section 50
2.1. Ag/C catalysts for e-CO₂RR 50
2.1.1. Fabrication of Ag electrode 50
2.1.2. Fabrication of Ag/C electrodes 50
2.1.3. Fabrication of Ag/acid-CB and Ag/acid-CNC electrodes 50
2.1.4. Investigation of Ag/C electrodes through micro-CT 51
2.1.5. Single cell test of e-CO₂RR 51
2.1.6. Physical Characterization 52
2.2. AgD-W/C electrocatalyst for solar-to-CO conversion 53
2.2.1. Synthesis of AgD-W/C 53
2.2.2. Preparation of AgD-W/C electrode 53
2.2.3. Fabrication of silicon solar cell 53
2.2.4. Single-cell test for e-CO₂RR 54
2.2.5. Physical characterization 55
2.3. Lipid ligand Ag-NPs catalyst for CO₂ electrolysis 56
2.3.1. Synthesis of lipid ligand Ag-NPs 56
2.3.2. Fabrication of Ag black, Ag-PTFE and Ag-NP electrodes 56
2.3.3. APT analysis 57
2.3.4. In-situ/operando XANES 57
2.3.5. In-situ/operando micro-CT 58
2.3.6. IL-TEM analysis of Ag black and Ag-NPs 58
2.3.7. e-CO2RR single-cell test 59
2.3.8. Physical Characterization 60
CHAPTER 3. DISCUSSION 61
3.1. Enhancing catalytic performance and selectivity in electrochemical reduction of CO₂ to CO: Guidelines for optimal carbon supports selection 61
3.2. AgD-W/C as efficient and stable electrocatalyst for solar-to-CO conversion via scalable photovoltaic-electrochemical system 88
3.3. Extrinsic hydrophobicity-controlled silver nanoparticles as stable and efficient catalyst for e-CO₂RR 127
CHAPTER 4. CONCLUSION 149
REFERENCES 150
Table 1.3.1. Standard Nernst (E*) and thermoneutral (En) voltages of low-temperature e-CO₂RR. 38
Table 1.3.2. Standard reduction potentials for e-CO₂R in aqueous solutions (V vs. RHE). 41
Table 3.2.1. The performance of the reported solar to CO conversion 126
Figure 1.1.1. The annual global climate changes in 1880-2022. 29
Figure 1.1.2. The compilation of United States Greenhouse gas sinks and emissions (1990-2021). 30
Figure 1.1.3. Global fossil CO₂ emissions in 1990-2022. 31
Figure 1.2.1. Carbon neutral goals by country to Net Zero Energy (NZE). 33
Figure 1.2.2. Energy related CO₂ emissions enforced by government net zero emissions pledge. 34
Figure 1.2.3. Sustainable energy future based on electrocatalysis. 35
Figure 1.4.1. Diagrams illustrating the potential energy for rate-determining step (RDS) of the oxygen desorption mechanism in the electrochemical oxide path in an alkaline solutions,... 46
Figure 1.5.1. Different electrochemical CO₂RR electrolyzers. (a) Aqueous-phase CO₂RR type, (b) Vapor-fed CO₂RR type employing an aqueous and (c) polymer electrolyte. 48
Figure 1.5.2. The trend for CO partial current density of different electrochemical CO₂RR electroyzers. 49
Figure 3.1.1. Characterization of various carbon materials employed as supports included low and high-magnification (inset) images using high-resolution transmission electron... 65
Figure 3.1.2. Morphology of Ag black and Ag/C electrodes (loading: 1 mg cm⁻²) was examined through scanning electron microscopy (SEM) images at both low (surface) and... 68
Figure 3.1.3. Morphology of Ag black electrode. (a-e) low and high-magnification SEM images of surface and (f) cross-section of Ag black. 69
Figure 3.1.4. Morphology of Ag/CB electrode. (a-d) low and high-magnification SEM images of surface, (e) cross-section of Ag/CB and (f) line scanning data of cross section... 70
Figure 3.1.5. Morphology of Ag/CNF electrode. (a-d) low and high-magnification SEM images of surface, (e) cross-section of Ag/CNF and (f) line scanning data of cross section... 71
Figure 3.1.6. Morphology of Ag/CNC electrode. (a-d) low and high-magnification SEM images of surface, (e) cross-section of Ag/CNC and (f) line scanning data of cross section... 72
Figure 3.1.7. Section 323 of a total 993 generated tomographic images of the Ag/CNC sample. 73
Figure 3.1.8. Micro-computed tomography (micro-CT) images of the three-dimensional structure. (a) Ag black, (b) Ag/CB, (C) Ag/CNF, and (d) Ag/CNC. Red color: Ag, Green... 74
Figure 3.1.9. CO₂RR performance of Ag black and Ag/C electrodes (area: 10cm², loading 1 mg cm⁻²) in 0.1 M KHCO₃ electrolyte in a zero-gap electrolyzer at a CO₂ flow rate of 200... 76
Figure 3.1.10. (a) Water contact angle (WCA) results for Ag black and Ag/C electrodes sprayed on GDL before (black sphere) and after the reaction (red sphere). X-ray... 79
Figure 3.1.11. XPS C1s of Ag/CNF before and after reaction. 80
Figure 3.1.12. XPS C1s spectra of (a) CNC and (b) acid treated CNC (denoted as CNC-acid). 81
Figure 3.1.13. (a) CO and H₂ Faradaic efficiency, (b) CO and H₂ partial current density of Ag/CNC and Ag/CNC-acid. 82
Figure 3.1.14. CO₂RR activity and HER using a 0.1 M KHCO₃electrolyte. Electrodes featuring CB, acid-CB, CNCs, and acid-CNC deposited on the GDL (loading: 1 mg cm⁻²)... 85
Figure 3.1.15. 3-cell stacked electrolyzer of the operation in serial configuration with Ag/C electrodes. (a) Schematic of the 3-stacked cell, and (b) total current versus cell voltage.... 87
Figure 3.2.1. Method of Synthesis and physical characterizations of AgD-W/C. (a) Schematic of synthesis method for AgD-W/C. (b, c) Low-magnification images captured by HR-TEM... 92
Figure 3.2.2. HR-TEM images. (a) Low- and (b) high-magnification of W-seed nanoparticles supported on amorphous carbon black. 93
Figure 3.2.3. Morphology of AgD-W/C. HR-TEM images of (a-c) Low- and high-magnification, and (d) the edge of AgD-W/C. 94
Figure 3.2.4. (a, b) High-magnification images of AgD-W/C using HR-TEM and HAADF-STEM. (c, d) EDS mapping data of AgD-W/C. (violet colour: Ag, green colour: W). 95
Figure 3.2.5. (a-d) The HR-TEM images and (e, f) the images of AgD-W/C surface through HAADF-STEM. 96
Figure 3.2.6. The annual global climate changes in 1880-2022. (a-b) High- and (c-f) low-magnification HR-STEM images for W (green) and Ag (purple) elements of AgD-W/C. 97
Figure 3.2.7. HR-TEM images of Ag supported on carbon (Ag/C) without W-seed. 98
Figure 3.2.8. XRD profiles of Ag black, W/C, and AgD-W/C electrodes 99
Figure 3.2.9. HR-TEM images. (a, b) Low- and high-magnification, and (c) the edge of Ag black. 100
Figure 3.2.10. Morphology of Ag black electrode before CO₂ reduction reaction (CO₂RR). (a-d) SEM images at the surface of Ag black electrode. (e, f) Cross-sectional SEM images... 101
Figure 3.2.11. Morphology of Ag black supported on carbon (Ag/C) electrode before CO₂ reduction reaction (CO₂RR). (a-d) SEM images at the surface of Ag black/C electrode. (e, f)... 102
Figure 3.2.12. Morphology of AgD-W/C electrode before CO₂ reduction reaction (CO₂RR). (a-d) SEM images at the of AgD-W/C electrode. (e, f) SEM images at the cross-section of... 103
Figure 3.2.13. CO₂RR activity of Ag black, W/C, and AgD-W/C electrodes in the zero-gap CO₂ electrolyzer. (a) Illsutiration of the electrolyzer. The anode utilized sprayed IrO₂... 106
Figure 3.2.14. Impedance of zero-gap CO₂RR device using Ag electrode for measuring ohmic resistance of system. 107
Figure 3.2.15. Various analysis for confirming properties of AgD-W/C. (a) CV curves for AgD-W/C, Ag/C, and Ag black electrodes were obtained using zero-gap CO₂ electrolyzer... 112
Figure 3.2.16. The pictures of WCA. Ag black and AgD-W/C electrodes. 113
Figure 3.2.17. Cyclic voltammetry of (a) Ag black, (b) carbon black, and (c) AgD-W/C electrode in 0.5 M KHCO₃ solution under CO₂ saturation (scan rate: 4, 6, 8 and 10 mV s⁻¹).... 114
Figure 3.2.18. CV curves for W/C and AgD-W/C were obtained utilizing zero-gap CO₂ electrolyzer. (cell voltage ranges: -1.0 V~1.5 V). The anode used was Pt/C, and the... 115
Figure 3.2.19. (a, b) Ex-situ XANES of Ag-based electrodes. In-situ/operando XANES profiles for (c) Ag black and (d) AgD-W/C electrode with different operating cell voltage. 116
Figure 3.2.20. W L₃-edge X-ray absorption near-edge structure (XANES) spectra of AgD-W/C under CO₂RR operating condition. W foil was measured as reference. 117
Figure 3.2.21. High-resolution XPS profiles. (a) C1s and (b) O1s of Ag black electrode before and after applied 3 V for activation. 118
Figure 3.2.22. Solar-driven CO₂RR configuration. (a) Illustration of conversion for solar to CO system with silicon solar cell (area: 120 cm²). The cathode utilized AgD-W/C on GDL,... 121
Figure 3.2.23. (a, b) (a) Electrolyte behavior when using carbon paper and foam type electrode used as the substrate of electrode. (b) J-V curves of CO₂electrolyzer with applied... 122
Figure 3.2.24. I-V curves of the CO₂ electrolyzer with AgD-W/C cathode and silicon based solar cell with 3~6 cells under AM 1.5 G. 123
Figure 3.2.25. Photographs of the solar-to-CO conversion system in realistic condition at the rooftop of the building. (a, b) Whole system consisting of solar-to-CO conversion, (c) solar... 124
Figure 3.2.26. Photographs of the solar-to-CO conversion photovoltaic-electrochemical system 125
Figure 3.3.1. Physical properties of the synthesized Ag-NP catalyst. (a) TEM image of the synthesized Ag-NP catalyst. (b) Box and histogram plots show the particle size distributions... 129
Figure 3.3.2. Illustration of the synthesis process of Ag-NP catalysts. 130
Figure 3.3.3. HR-TEM images of Ag-NP catalyst for 2, 3, and 5-fold verification; scale bar=3 nm 131
Figure 3.3.4. Single-cell performance of the Ag-NP catalyst. (a) Faradaic efficiency of CO, and (b) CO partial current density versus applied cell voltage in a zero-gap CO₂ electrolyzer... 134
Figure 3.3.5. Schematic of electrochemical CO₂ reduction experimental setup. 135
Figure 3.3.6. The components and assembly of zero-gap CO₂ electrolyzer system using gas diffusion layer (GDL). 136
Figure 3.3.7. CO₂RR performance and HER measured for Ag black and Ag-NP catalysts in 0.1 M KHCO₃ electrolyte. (a) Total current density, (b) H₂ faradaic efficiency, and (c) H₂... 137
Figure 3.3.8. CO₂RR performance and HER measured for Ag-PTFE catalysts in 0.1 M KHCO₃ electrolyte. (a) Total current density, (b) CO partial current density, and (c) H₂... 138
Figure 3.3.9. Durability test of the Ag-PTFE (20 wt%) at 3.4 V for 50 h. Faradaic efficiency and selectivity of CO and H₂ measured during the durability tests. The electrodes were... 139
Figure 3.3.10. Morphology and phase change during the CO₂RR. IL-TEM images of the (a, b) Ag black and (c, d) Ag-NP catalysts, (a, c) before and (b, d) after the CO₂RR. (e, f) In-... 142
Figure 3.3.11. Visual analyses of the influence of electrode hydrophobicity on the CO₂RR. (a) A schematic representation of the zero-gap CO₂ electrolyzer used for the in-... 145
Figure 3.3.12. System of in-situ/operando synchrotron computed tomography (CT) analysis with the homemade electrochemical zero-gap CO₂RR electrolyzer. 146
Figure 3.3.13. Photo of a synchrotron-based X-ray computed tomography (CT) flow cell and system for electrochemical CO₂reduction reaction (CO₂RR). 147
Figure 3.3.14. WCA results after CO₂RR at 3.0 V and 3.2 V. (a) Ag black and (b) Ag-NP. 148