Title Page
ABSTRACT
국문 초록
PREFACE
Contents
NOMENCLATURE 27
1. Introduction 31
1.1. Introduction of photoelectrochemical water splitting 31
1.2. Advantages of functional structures in photoelectrochemical device 37
1.2.1. Limitation of film type photoelectrochemical device 37
1.2.2. Advantages of structured photoelectrochemical device 39
1.3. Fabrication process of functional structures 43
1.3.1. Top-down process of structures 43
1.3.2. Bottom-up process of structures 45
1.4. Reference 46
2. Fabrication of BiVO₄ materials 53
2.1. BiVO₄ photoanode via sputtering 53
2.1.1. Introduction 53
2.1.2. Experimental Section 56
2.1.3. Result and discussion 57
2.1.4. Summary 73
2.2. Moth-eye structured BiVO₄ photoanode via e-beam evaporation 74
2.2.1. Introduction 74
2.2.2. Experimental Section 77
2.2.3. Result and discussion 80
2.2.4. Summary 103
2.3. Nanostructured BiVO₄ photoanode via oblique angle deposition 104
2.3.1. Introduction 104
2.3.2. Experimental Section 106
2.3.3. Result and discussion 108
2.3.4. Summary 143
2.4. Reference 144
3. Functional structured photoelectrochemical devices 152
3.1. Fabrication of structured FTOs 152
3.1.1. Introduction 152
3.1.2. Experimental Section 155
3.1.3. Result and discussion 159
3.1.4. Summary 166
3.2. BiVO₄ photoanode on structured FTOs 167
3.2.1. Introduction 167
3.2.2. Experimental Section 170
3.2.3. Result and discussion 172
3.2.4. Summary 195
3.3. WO₃ nanoflakes/BiVO₄ on micro-cone structured FTO 196
3.3.1. Introduction 196
3.3.2. Experimental Section 198
3.3.3. Result and discussion 200
3.3.4. Summary 230
3.4. Reference 231
4. Measurements 236
4.1. Characterization 236
4.2. PEC performance measurements 237
5. Couclusion 239
Table 2.1. Summary of studies on BiVO₄ fabricated via sputtering. 70
Table 2.2. EIS Nyquist plot results for the BVO-A and BVO-V photoanodes obtained using the Z-view software. 71
Table 2.3. Specifications of the hole patterns. 99
Table 2.4. Surface area and surface area ratio of BVO-0, BVO-80, and BVO-85 measured by atomic force microscopy (AFM; surface area of 9.0 µm²). 119
Table 2.5. The Jabs and ηabs values of BVO-0, BVO-80, and BVO-85[이미지참조] 134
Table 2.6. Comparison of the photocurrent densities with those of BiVO₄ photoanode studies fabricated by e-beam evaporation. 140
Table 3.1. Comparison of the sheet resistivity, average transmittance, and figure of merit for the F-FTO and MC-FTO. 165
Table 3.2. Information on the diameter, pitch, and height for MP patterns 179
Table 3.3. Nyquist plot results for BVO-F, BVO-MP1, and BVO-MP2, obtained using Z-view software 194
Table 3.4. Comparison of the sheet resistivity, average transmittance, and figure of merit for the flat FTO and micro-cone structured FTO. 203
Table 3.5. Comparison of the sheet resistivity, resistivity, mobility, and carrier concentration for flat FTO and micro-cone structured FTO, obtained via Hall measurements. 204
Table 3.6. Comparison of loading amount of active material for B-WO₃/BiVO₄ and FB-WO₃/BiVO₄ 210
Table 3.7. Peak area ratio and normalized peak intensity ratio of the (002), (020), and (200) peaks of WO₃ in the XRD patterns for B-WO₃/BiVO₄ and FB-WO₃ /BiVO₄. 211
Table 3.8. Band positions (EV, EC, and Ef) and bandgaps of B-WO₃/BiVO₄ and FB-WO₃/BiVO₄.[이미지참조] 219
Table 3.9. Nyquist-plot results for B-WO₃/BiVO₄ and FB-WO₃/BiVO₄, obtained using the Z-view software. 226
Figure 1.1. (a) Band structure of photoelectrochemical water splitting materials and energy level of OER and HER. (b) Schematic diagram of mechanism of... 35
Figure 1.2. Schematic diagram of (a) photocatalyst, (b) photoelectrochemical cell, (c) PEC-PSC (photoelectrochemical device- perovskite solar cell) tandem cell. 36
Figure 1.3. Schematic diagram of film type PEC device. 38
Figure 1.4. (a) Photoimage of moth-eye, (b) SEM images of moth-eye [J.Y. SUN et al.], and (c) schematic diagram of moth-eye effect. 41
Figure 1.5. Schematic diagram of structured PEC device. 42
Figure 2.1. (a) Bulk/surface atomic ratios of Bi/V for BVO-A and BVO-V, which were measured via ICP-AES and XPS, respectively. (b) Low-resolution TEM image... 60
Figure 2.2. SEM images of (a-b) BVO-A and (c-d) BVO-V. (e) Crystallite size and grain size of the BiVO₄ photoanodes. 62
Figure 2.3. (a) Photograph of BVO-A and BVO-V. (b) Transmittance, (c) reflectance, and (d) absorption spectra of BVO-A and BVO-V obtained via UV-vis spectroscopy. 64
Figure 2.4. Refractive index (n) and absorption coefficient (k) of (a) BVO-A and (b) BVO-V measured via ellipsometry. 65
Figure 2.5. Bandgap calculation for (a) BVO-A and (b) BVO-V based on UV-vis spectroscopy. 66
Figure 2.6. Comparison of the PEC properties of BVO-A and BVO-V. (a) J-V measurements performed in a 0.5 M phosphate buffer solution (pH 7.1) under AM... 69
Figure 2.7. J-t measurements performed in a 0.5 M phosphate buffer solution under 1.5G illumination. 72
Figure 2.8. Schematic of M-BVO fabrication process 79
Figure 2.9. Characterization of BiVO₄ fabricated via e-beam evaporation and V calcination: (a) XRD spectrum and XPS spectra of (b) Bi 4f, (c) V 2p, and (d) O 1s.... 82
Figure 2.10. SEM images of (a, b) F-BVO and (c, d) M-BVO. 2D and 3D AFM images of (e, f) F-BVO and (g, h) M-BVO. 84
Figure 2.11. TEM analysis of M-BVO: (a) low-resolution TEM image, (b) high-resolution TEM image, (c) FFT of whole HR-TEM image. TEM-EDS mapping... 85
Figure 2.12. Optical properties of BiVO₄ photoanode: UV-vis (a) transmittance, (b) reflectance, and (c) calculated absorption spectra. (d) Calculated effective... 89
Figure 2.13. n and k values of a) SnO₂ and b) BiVO₄ measured using ellipsometry. 90
Figure 2.14. Calculated effective refractive indices of M-BVO at wavelengths of a) 350 nm, b) 400 nm, c) 500 nm, d) 550 nm. 91
Figure 2.15. Specular reflectance of F-BVO with a) s-polarized and c) p-polarized light and of M-BVO with b) s-polarized and d) p-polarized light. 92
Figure 2.16. Mean specular reflectance data for a) s-polarized, b) p-polarized, and c) nonpolarized light. 93
Figure 2.17. (a) J-V curves of F-BVO and M-BVO measured in a solution of 0.5 M phosphate buffer (pH 7.2) under 1-sun illumination. (b) J-t curve and (c) IPCE of... 96
Figure 2.18. (a) Photocurrent density versus F-BVO thickness (b) Mott-Schottky analysis data for F-BVO with thickness of 150 nm. 97
Figure 2.19. (a) APCE of F-BVO and M-BVO at 1.23 V RHE measured in a 0.5 M phosphate buffer solution under AM 1.5G illumination. (b) ABPD data for F-BVO... 98
Figure 2.20. (a) Jsulfite-V curves of F-BVO and M-BVO measured in a solution of 0.5 M phosphate buffer containing 0.5 M Na₂SO₃ under 1-sun illumination. (b)...[이미지참조] 102
Figure 2.21. Schematic illustration of the fabrication process of nanostructured BVO. 109
Figure 2.22. SEM images of fabricated Bi₂O₃ NH with different incident angles of the source flow (θ) during the OAD process: top-view and cross-sectional view of... 112
Figure 2.23. The calculation of the Bi₂O₃ nanohelix coverage using ImageJ software: (a) BO-80 and (b) BO-85. 113
Figure 2.24. Morphology of BVOs for different OAD angle: SEM images of (a) BVO-0, (b) BVO-80, and (c) BVO-85. 3D AFM images of (d) BVO-0, (e) BVO-80,... 114
Figure 2.25. Scanning electron microscopy (SEM) images of (a) BVO-0, (b) BVO-80, and (c) BVO-85. 115
Figure 2.26. Scanning The calculation of the porosity using ImageJ software: (a) BVO-80 and (b) BVO-85. 116
Figure 2.27. The respective two- and three-dimensional AFM images of (a, b) BO-0, (c, d) BO-80, and (d, e) BO-85. 117
Figure 2.28. The respective two- and three-dimensional AFM images of (a, b) BVO-0, (c, d) BVO-80, and (d, e) BVO-85. 118
Figure 2.29. Compositional analysis of nanostructured BiVO₄: (a) XRD spectra and (b) stoichiometric ratio of V/Bi obtained using ICP-AES for BVO-0, BVO-80,... 122
Figure 2.30. The narrow-scan X-ray diffraction (XRD) spectra of BVO-0, BVO-80, and BVO-85. 123
Figure 2.31. The narrow-scan X-ray photoelectron spectroscopy (XPS) results for (a-d) BVO-0, (e-h) BVO-80, and (i-l) BVO-85. 124
Figure 2.32. (a) High-resolution transmission electron image (TEM) and (b) fast Fourier transform (FFT) image of BVO. 125
Figure 2.33. Contact angles between the V precursor and (a) BO-0, (b) BO-80, and (c) BO-85. 126
Figure 2.34. (a) Image of BVO-0, BVO-80, and BVO-85. (b) Transmittance and (c) absorption graph of BVO-0, BVO-80, and BVO-85 measured by UV-vis... 129
Figure 2.35. The Tauc plot for the deposited Bi₂O₃ based on UV-Vis spectroscopy. 130
Figure 2.36. The tauc plot for (a) BVO-0, (b) BVO-80, and (c) BVO-85 based on UV-vis spectroscopy. 131
Figure 2.37. The reflectance graph of BVO-0, BVO-80, and BVO-85, as determined by UV-Vis with an integrating sphere. 132
Figure 2.38. Photon flux of the AM 1.5 G solar spectrum, BVO-0, BVO-80, and BVO-85. 133
Figure 2.39. The non-polarized specular reflectance graph of (a) BVO-0, (b) BVO-80, and (c) BVO-85. The p-polarized specular reflectance graph of (d) BVO-... 135
Figure 2.40. Mean angle-dependent specular reflectance of (a) p-polarized light and (b) s-polarized light for BVO-0, BVO-80, and BVO-85. 136
Figure 2.41. Comparison of the photoactivity of BVO-0, BVO-80, and BVO-85 under 1-sun illumination. (a) LSV curve measured in a 0.5-M phosphate buffer... 139
Figure 2.42. Linear sweep voltammetry (LSV) curve for BVO-0/Co-Pi, BVO-80/Co-Pi, BVO-85/Co-Pi measured in a 0.5 M phosphate buffer solution under 1-... 141
Figure 2.43. Mechanism diagram of PEC water splitting at nanostructured BiVO₄ photoanode. 142
Figure 3.1. Schematic diagram of direct printing. 157
Figure 3.2. Schematic diagram of Mist-CVD. 158
Figure 3.3. SEM images of flat FTO (a, b) and micro-cone structured FTO (c, d) deposited with carrier gas of 80% N₂ and 20% O₂. SEM images of flat FTO (e, f)... 160
Figure 3.4. SEM images of nano-pillar structured FTO (a, b), micro-pillar structured FTO (c, d), mesh structured FTO (e, f), and micro-cone structured FTO... 163
Figure 3.5. UV-vis optical transmittance (a) and diffuse transmittance (b) for the two types of FTOs. (c) Mobility and carrier concentration as well as (d) sheet... 164
Figure 3.6. (a) XRD spectra; and high-resolution, narrow-scan XPS spectra of the sample: (b) Bi 4f, (c) V 2p, and (d) O 1s. 174
Figure 3.7. BiVO₄: (a) TEM image, (b) high-resolution TEM (HR-TEM) image, (c) FFT of the whole HR-TEM image, (d) low-resolution TEM image for line... 175
Figure 3.8. (a) SEM images showing overall process: (a, b) HSQ-MP1, (c, d) HSQ-MP2, (e, f) FTO-MP1, (g, h) FTO-MP2, (i, j) BVO-MP1, and (k, l) BVO-MP2. 178
Figure 3.9. Scanning electron microscopy (SEM) images of (a) top and (b) side of BVO-F. 180
Figure 3.10. Focused ion beam (FIM) SEM image of BVO-MP1. 181
Figure 3.11. TEM EDS mapping images of (a) BVO-MP1: (b) Sn, (c) V, (d) O, (e) Bi, (f) Si, and (g) Pt. 182
Figure 3.12. Plots of (a) mobility and bulk carrier concentration, and (b) sheet resistance and resistivity, and (c) transmittance for FTO-F, FTO-MP1, and FTO-MP2. 183
Figure 3.13. 2D and 3D AFM images of (a) BVO-F, (b) BVO-MP1, and (c) BVO-MP2. 184
Figure 3.14. (a) Transmittance, (b) reflectance, and (c) absorption graph of BVO-F, BVO-MP1, and BVO-MP2 investigated via UV-vis spectroscopy. 187
Figure 3.15. Electron flux results of (a) AM 1.5G solar spectrum and (b) BVO-F, BVO-MP1, and BVO-MP2. 188
Figure 3.16. Current density of BiVO₄ photoanodes with different deposition thickness of BiVO₄ in a 0.5 M phosphate buffer solution under AM 1.5G illumination... 192
Figure 3.17. Comparison of the PEC performance of BVO-F, BVO-MP1, and BVO-MP2. (a) J-V measurements conducted in a 0.5-M phosphate buffer solution... 193
Figure 3.18. SEM images of flat FTO (a, b) and micro-cone structured FTO (c, d). UV-vis optical transmittance for the two types of FTO (e). 202
Figure 3.19. SEM images of B-WO₃ (a, b) and FB-WO₃ (c, d) NFs. 208
Figure 3.20. SEM images of B-WO₃ /BiVO₄ (a, b) and FB-WO₃/BiVO₄ (c, d). (e) XRD spectra of the B-WO₃/BiVO₄ and FB-WO₃/BiVO₄. TEM image (f) and... 209
Figure 3.21. High-resolution SEM image (a) and EDS mapping (b) of a WO₃ NF for the TEM sample. Schematic representation of a WO₃ NF (c). 212
Figure 3.22. High-resolution TEM images of BiVO₄ coated on WO₃ NFs with different facets. 213
Figure 3.23. EDS mapping images of (a) B-WO₃/BiVO₄ and (b) FB-WO₃/BiVO₄. 214
Figure 3.24. XPS results for (a) B-WO₃/BiVO₄ and (b) FB-WO₃/BiVO₄. 215
Figure 3.25. Ultraviolet photoelectron spectra (a) and optical bandgap energy (b) of WO₃ NFs on flat (red) and microcone-patterned (blue) FTO. Ultraviolet... 218
Figure 3.26. Comparison of the PEC properties of B-WO₃/BiVO₄ and FB-WO₃/BiVO₄. (a) Photocurrent density-potential (J-V) measurements performed in a... 224
Figure 3.27. IPCE and APCE of B-WO₃ and FB-WO₃ measured at 1.23 VRHE.[이미지참조] 225
Figure 3.28. EIS Nyquist plot for B-WO₃ and FB-WO₃ measured under AM 1.5G illumination at 1.23 VRHE.[이미지참조] 227
Figure 3.29. EIS Reflectance spectra of B-WO₃/BiVO₄ and FB-WO₃/BiVO₄, obtained via UV-vis spectroscopy. 228
Figure 3.30. (a) Electron flux of the AM 1.5G solar spectrum. (b) Electron flux of B-WO₃/BiVO₄ and FB-WO₃/BiVO₄ photoanodes. 229