Title Page
Abstract
Contents
Part 1. Electrolyte engineering: A Unifying Mechanism for Cation Effect Modulating C1 and C2 Productions from CO₂ Electroreduction 13
Ⅰ. Introduction 13
Ⅱ. Methods 15
2.1. DFT-CES simulations 15
2.2. Electrode preparations 16
2.3. Electrochemical investigations 17
Ⅲ. Results and discussion 19
3.1. To be, or not to be coordinated by a cation 19
3.2. Nature of cation-coupled electron transfer 21
3.3. Cation concentration-dependent Nernstian shifts 23
3.4. CCET kinetics controlled by surface charge density 25
3.5. Tuning the surface charge density for enhanced C-C coupling 27
Ⅳ. Conclusions 28
Ⅴ. References 29
Part 2. Electrode engineering: Interfacial field-driven OOH* stabilization and its role in selectivity of single-atom cobalt catalyst in oxygen reduction 81
Ⅰ. Introduction 81
Ⅱ. Experimental 84
2.1. Catalysts Synthesis and O₃-treatment 84
2.2. Electrochemical Characterizations 85
2.3. Physico-chemical Characterizations 87
Ⅲ. Results and discussions 88
3.1. Synthesis and physical characterizations of the CoNC catalysts 88
3.2. Oxygen reduction selectivity of the CoNC catalysts 90
3.3. Non-catalytic parameter determining ORR electrocatalysis 92
Ⅳ. Conclusions 94
Ⅴ. References 95
Overall conclusions 119
Curriculum Vitae 121
Part 2. Electrode engineering: Interfacial field-driven OOH* stabilization and its role in selectivity of single-atom cobalt catalyst in oxygen reduction 11
Table 1. Structural parameters extracted from the Co K-edge EXAFS fitting of O₃-treated CoNC SACs. (S₀²=0.82) 116
Part 1. Electrolyte engineering: A Unifying Mechanism for Cation Effect Modulating C1 and C2 Productions from CO₂ Electroreduction 9
Figure 1. Electrochemical flow cell. 33
Figure 2. RC circuit for fitting obtained impedance data. 34
Figure 3. Map of cation-(un)coordinated intermediates during CO₂RR. 35
Figure 4. Full-scale snapshots of the charged interface with various intermediates from DFT-CES simulations. 36
Figure 5. Electrostatic potential profiles, ϕ, across the charged interfaces, calculated using DFT-CES. 37
Figure 6. Distance between K⁺ and cation-coordinated adsorbates. 38
Figure 7. Radial distribution function, g(r), calculated using the DFT-CES at -1.0 VSHE.[이미지참조] 39
Figure 8. Radial distribution function, g(r), calculated using the DFT-CES at -0.5 VSHE, that is the potential at point of zero charge, EPZC.[이미지참조] 40
Figure 9. Reaction energy diagrams and cation-coupled electron transfer. 41
Figure 10. Reaction energy diagram for CO-to-CH₄ and CO-to-C₂H₄ reaction paths on Cu(100), calculated using DFT-CES energetics. 43
Figure 11. Reaction energy diagrams for CO₂-to-CO reaction path on Cu(100), calculated using DFT-CES energetics. 44
Figure 12. Change of cation-coodrinating structure of *CO₂ and *OCCO during DFT-CES iterations. 45
Figure 13. Projected density of states (PDOS) calculated using DFT-CES. 46
Figure 14. Physical characterizations of Ag-PTFE electrode. 47
Figure 15. Electrochemical CO₂RR and CORR in various electrolytes. 48
Figure 16. Faradaic efficiency (FE) of CO₂RR on the Ag electrode in KOH electrolytes. 49
Figure 17. CO₂-to-CO conversion on the Ag electrode in KOH + K₂CO₃ electrolytes. 50
Figure 18. Faradaic efficiency (FE) of CO₂RR on the Ag electrode in KOH + K₂CO₃ electrolytes. 51
Figure 19. Electrolyte pHs. 52
Figure 20. Physical characterizations of Au-PTFE electrode. 53
Figure 21. CO₂-to-CO conversion on the Au electrode. 54
Figure 22. Physical characterizations of the NiNC electrode. 55
Figure 23. CO₂-to-CO conversion on the NiNC electrode. 56
Figure 24. CO₂-to-CO conversion on the Ag electrode in acid, neutral, and alkaline electrolytes. 57
Figure 25. Physical characterizations of Cu-PTFE electrode. 58
Figure 26. Electrochemical CO₂RR on the Cu electrode. 59
Figure 27. Faradaic efficiency (FE) of CO₂RR on the Cu electrode. 60
Figure 28. Electrochemical CO₂RR on the Cu electrode in various MOH electrolytes. 61
Figure 29. Reaction kinetic study of CO₂RR on the Cu electrode. 62
Figure 30. Electrochemical CORR on the Cu electrode in KOH + K₂CO₃ electrolytes. 63
Figure 31. Faradaic efficiency (FE) of CORR on the Cu electrode. 64
Figure 32. Electrochemical CO₂RR on the Ag electrode in various M₂CO₃ electrolytes. 65
Figure 33. Electrochemical CORR on the Cu electrode in various MOH electrolytes. 66
Figure 34. EPZC measurements.[이미지참조] 67
Figure 35. Cdiff curves of the Ag electrode.[이미지참조] 68
Figure 36. Cdiff curves of the Cu electrode.[이미지참조] 70
Figure 37. Reaction kinetic studies. 71
Figure 38. Ionomer effects on the CO₂RR. 73
Figure 39. Boosted C₂H₄ formation on the Nafion-coated Cu electrode. 74
Figure 40. Ionomer effects on the CORR. 75
Figure 1. The schematic illustration of O₃-treatment and real device (ozone generator) set-up image. 98
Figure 2. Structural charaterizations of samples. 99
Figure 3. XPS-N₁s analysis incorporated into the carbon matrix of CoNCs as dominant forms of pyridinic-, pyrrolic-, and graphitic-N.[이미지참조] 100
Figure 4. The atomic percentages of different nitrogen functional groups within the pristine and O3-treated CoNCs. 101
Figure 5. BET surface area and total Co content in catalysts for O₃-treatment time. 102
Figure 6. Structural characterization of the pristine and O₃-treated CoNCs. 103
Figure 7. HAADF-STEM images of a selected area on O₃-treated CoNCs, showing the atomic distribution of Co atoms on the carbon substrates. 104
Figure 8. Oxygen content of samples prepared at different O3-treatment time by XPS-O₁s and EA analysis.[이미지참조] 105
Figure 9. Co 2p XPS spectra of the pristine and O₃-treated CoNCs. 106
Figure 10. The Co K-edge XANES spectra of the pristine and O₃-treated CoNCs. 107
Figure 11. Electrochemical ORR measurement of the pristine and O₃-treated CoNCs at 0.1 M HClO₄ electrolyte. 108
Figure 12. Electrochemical poly-Pt ORR measurements with various pH conditions. 109
Figure 13. Electrochemical ORR measurement of the pristine and O3-treated CoNCs at 0.2 M PBS electrolyte. 110
Figure 14. Electrochemical ORR measurement of the pristine and O3-treated CoNCs at 0.1 M KOH electrolyte. 111
Figure 15. In situ poisoning test for O₃-treated CoNC catalysts. 112
Figure 16. The ORR activity retentions of two electron and four electron ORR pathway at 0.7 VRHE and 0.8 VRHE with various pH electrolytes.[이미지참조] 113
Figure 17. The key factor of ORR kinetics and pathway for the pristine and O₃-treated CoNCs: surface charging. 114
Figure 18. Volcano-like correlation curves with different EORRs.[이미지참조] 115
Note 1. Derivation of a kinetic equation for CO₂-to-C₂H₄ conversion. 76
Note 2. Thermodynamics vs. Kinetics: Validation of activity comparison upon thermodynamically (Nernstianly) [M⁺]-corrected CCE potential scale. 79
Note 1. Calculation of partial kinetic current density for electrochemical H₂O₂ production. 117