氧化亞銅晶體在導電性、光催化活性和光學特性上，已被證明具有晶面效應。然而，氧化亞銅晶體在光電化學特性上的晶面效應仍不清楚。在本篇研究中，我們合成了可調控尺寸的立方體、立方八面體、八面體和菱形十二面體的氧化亞銅進行光電化學分析。因為能隙的偏移和粒徑大小相關，粒徑大小的影響也需被納入考量。在正面照光下，立方體皆表現出遠比其他形狀還強的光電流響應，這代表在光電化學特性上，晶面效應的重要性要大於能隙位移的影響，且氧化亞銅的{100}面具有最佳的光電轉換效率。與此相對，立方八面體的表現居中，並未展現如文獻所提之晶面接面對光催化性質有增強的效果。菱形十二面體表現微弱，而八面體則是最弱。為了更詳細地解釋光電化學的活性表現，從電化學量測得以建構出氧化亞銅晶體的能帶圖、能帶彎曲和光伏電壓，發現和光電化學實驗的結果無清楚的相關性。為了檢視電荷傳遞的過程，採用了背面照光的光電化學量測。尺寸居中的立方體光電化學活性提升較其他尺寸的立方體多，展現出尺寸的效應。菱形十二面體表現出最大的活性提升，表示堆疊的{110}面其電洞傳遞通過氧化亞銅-氧化銦錫接面的受限程度最大。我們可以得出的結論是氧化亞銅晶體在光電化學特性上具有明顯的晶面效應和些微的尺寸效應，可由受限於氧化亞銅-氧化銦錫接面之間的電洞傳遞主導。

Cu2O crystals have been demonstrated to show facet-dependent electrical conductivity, photocatalytic activity and optical properties. However, the facet effects on photoelectrochemical (PEC) properties of Cu2O crystals are still unclear. Herein, we have synthesized Cu2O cubes with tunable sizes, cuboctahedra (CO), octahedra (Oct), and rhombic dodecahedra (RD) for PEC analysis. The influence of particle size is also considered because of the size-related band gap shifts. Under front-side illumination, cubes show much better photocurrent responses than other shapes do. This suggests facet effect is more significant than band gap shifts for PEC properties, and the Cu2O {100} faces have the best photon-to-current efficiency. In contrast, the performance of CO is moderate, showing no facet junction effect. RD are weak, and Oct are the weakest. To interpret the PEC performances in detail, band diagram, band bending, and photovoltage of Cu2O crystals have been obtained, but the results do not show clear correlation to the measured PEC activities. To investigate the charge pathway effect, the PEC measurements under back-side illumination were also performed. The M-cubes display more enhanced PEC performance than other sizes of cubes, exhibiting the size effect. RD display the strongest enhancement in performance, showing their stacked {110} faces presents the most limited hole transport across the Cu2O‒ITO interface. We can conclude that PEC properties of Cu2O crystals are strongly facet-dependent and moderately size-dependent, with the hole transport across the Cu2O‒ITO interface playing a significant role.

摘要 i
Abstract ii
致謝 iv
Table of Contents v
List of Figures vii
List of Tables xii
List of Schemes xiii
Chapter 1. Introduction 1
1.1. Facet-Dependent Properties of Cu2O Crystals 1
1.2. Photoelectrochemical Water Splitting 5
1.3. Band Diagram Establishment 11
1.4. Facet Effects of Cu2O on PEC HER 14
1.5. Facet Junction of Semiconductor Crystals 16
1.6. Motivation 18
Chapter 2. Experimental Methods 20
2.1. Chemicals 20
2.2. Synthesis of Size-Tunable Cu2O Cubes 20
2.3. Synthesis of Cu2O Octahedra and Rhombic Dodecahedra 21
2.4. Synthesis of Cu2O Cuboctahedra 22
2.5. Preparation of Cu2O/ITO Photocathodes 23
2.6. Instrumentation 24
2.7. EC and PEC Measurements 24
2.7.1. LSV, CA, and OCP Measurements 25
2.7.2. ECSA Analysis 26
2.7.3. EIS and Mott‒Schottky Analysis 26
Chapter 3. Results and Discussion 27
Chapter 4. Conclusion 52
Chapter 5. References 53

1. Tan, C-S.; Hsu, S.-C.; Ke, W.-H.; Chen, L.-J.; Huang, M. H. Facet-Dependent Electrical Conductivity Properties of Cu2O Crystals. Nano Lett. 2015, 15, 2155-2160.
2. Chu, C.-Y.; Huang, M. H. Facet-Dependent Photocatalytic Properties of Cu2O Crystals Probed by Using Electron, Hole and Radical Scavengers. J. Mater. Chem. A 2017, 5, 15116-15123.
3. Huang, J.-Y.; Madasu, M.; Huang, M. H. Modified Semiconductor Band Diagrams Constructed from Optical Characterization of Size-Tunable Cu2O Cubes, Octahedra, and Rhombic Dodecahedra. J. Phys. Chem. C 2018, 122, 13027-13033.
4. Tan, C.-S.; Huang, M. H. Surface-Dependent Band Structure Variations and Bond-Level Deviations in Cu2O. Inorg. Chem. Front. 2021, 8, 4200-4208.
5. Hisatomi, T.; Kubota, J.; Domen, K. Recent Advances in Semiconductors for Photocatalytic and Photoelectrochemical Water Splitting. Chem. Soc. Rev. 2014, 43, 7520-7535.
6. Kment, S.; Riboni, F.; Pausova, S.; Wang, L.; Wang, L.; Han, H.; Hubicka, Z.; Krysa, J.; Schmuki, P.; Zboril, R. Photoanodes Based on TiO2 and Alpha-Fe2O3 for Solar Water Splitting - Superior Role of 1D Nanoarchitectures and of Combined Heterostructures. Chem. Soc. Rev. 2017, 46, 3716-3769.
7. Trześniewski, B. J.; Smith, W. A. Photocharged BiVO4 Photoanodes for Improved
Solar Water Splitting. J. Mater. Chem. A 2016, 4, 2919-2926.
8. Ning, F.; Shao, M.; Xu, S.; Fu, Y.; Zhang, R.; Wei, M.; Evans, D. G.; Duan, X. TiO2/Graphene/NiFe-Layered Double Hydroxide Nanorod Array Photoanodes for Efficient Photoelectrochemical Water Splitting. Energy Environ. Sci. 2016, 9, 2633-2643.
9. Bagal, I. V.; Chodankar, N. R.; Hassan, M. A.; Waseem, A.; Johar, M. A.; Kim, D.-H.; Ryu, S.-W. Cu2O as an Emerging Photocathode for Solar Water Splitting - A Status Review. Int. J. Hydrog. Energy 2019, 44, 21351-21378.
10. Aroonratsameruang, P.; Chakthranont, P.; Pattanasattayavong, P. The Cause of Limited Photoelectrochemical Water Reduction Performance of Co3O4 Photocathodes. Mater. Chem. Phys. 2021, 270, 124834.
11. Poldme, N.; O’Reilly, L.; Fletcher, I.; Portoles, J.; Sazanovich, I. V.; Towrie, M.; Long, C.; Vos, J. G.; Pryce, M. T.; Gibson, E. A. Photoelectrocatalytic H2 Evolution from Integrated Photocatalysts Adsorbed on NiO. Chem. Sci. 2019, 10, 99-112.
12. Yang, Y.; Xu, D.; Wu, Q.; Diao, P. Cu2O/CuO Bilayered Composite as a High-Efficiency Photocathode for Photoelectrochemical Hydrogen Evolution Reaction. Sci. Rep. 2016, 6, 35158.
13. Jian, J.; Kumar, R.; Sun, J. Cu2O/ZnO p–n Junction Decorated with NiOx as a
Protective Layer and Cocatalyst for Enhanced Photoelectrochemical Water Splitting.
ACS Appl. Energy Mater. 2020, 3, 10408-10414.
14. Kunturu, P. P.; Huskens, J. Efficient Solar Water Splitting Photocathodes Comprising a Copper Oxide Heterostructure Protected by a Thin Carbon Layer. ACS Appl. Energy Mater. 2019, 2, 7850-7860.
15. Wang, P.; Wu, H.; Tang, Y.; Amal, R.; Ng, Y. H. Electrodeposited Cu2O as Photoelectrodes with Controllable Conductivity Type for Solar Energy Conversion. J. Phys. Chem. C 2015, 119, 26275-26282.
16. Joe, J.; Yang, H.; Bae, C.; Shin, H. Metal Chalcogenides on Silicon Photocathodes for Efficient Water Splitting: A Mini Overview. Catalysts 2019, 9, 149.
17. Antony, R. P.; Zhang, M.; Zhou, K.; Loo, S. C. J.; Barber, J.; Wong, L. H. Synergistic Effect of Porosity and Gradient Doping in Efficient Solar Water Oxidation of Catalyst-Free Gradient Mo:BiVO4. ACS Omega 2018, 3, 2724-2734.
18. Hankin, A.; Bedoya-Lora, F. E.; Alexander, J. C.; Regoutz, A.; Kelsall, G. H. Flat Band Potential Determination: Avoiding the Pitfalls. J. Mater. Chem. A 2019, 7, 26162-26176.
19. Wei, Q.; Wang, Y.; Qin, H.; Wu, J.; Lu, Y.; Chi, H.; Yang, F.; Zhou, B.; Yu, H.; Liu, J. Construction of RGO Wrapping Octahedral Ag-Cu2O Heterostructure for Enhanced Visible Light Photocatalytic Activity. Appl. Catal. B 2018, 227, 132-144.
20. Zare, M.; Solaymani, S.; Shafiekhani, A.; Kulesza, S.; Talu, S.; Bramowicz, M.
Evolution of Rough-Surface Geometry and Crystalline Structures of Aligned TiO2 Nanotubes for Photoelectrochemical Water Splitting. Sci. Rep. 2018, 8, 10870.
21. Miao, B.; Iqbal, A.; Bevan, K. H. Utilizing Band Diagrams To Interpret the Photovoltage and Photocurrent in Photoanodes: A Semiclassical Device Modeling Study. J. Phys. Chem. C 2019, 123, 28593-28603.
22. Liu, C.; Chang, Y. H.; Chen, J.; Feng, S. P. Electrochemical Synthesis of Cu2O Concave Octahedrons with High-Index Facets and Enhanced Photoelectrochemical Activity. ACS Appl. Mater. Interfaces 2017, 9, 39027-39033.
23. Nian, J.-N.; Hu, C.-C.; Teng, H. Electrodeposited P-type Cu2O for H2 Evolution from Photoelectrolysis of Water Under Visible Light Illumination. Int. J. Hydrog. Energy 2008, 33, 2897-2903.
24. Lin, Z.; Li, L.; Yu, L.; Li, W.; Yang, G. Dual-functional Photocatalysis for Hydrogen Evolution from Industrial Wastewaters. Phys. Chem. Chem. Phys. 2017, 19, 8356-8362.
25. Mao, X.; Chen, P. Inter-Facet Junction Effects on Particulate Photoelectrodes. Nat. Mater. 2022, 21, 331-337.
26. Ho, J.-Y.; Huang, M. H. Synthesis of Submicrometer-Sized Cu2O Crystals with Morphological Evolution from Cubic to Hexapod Structures and Their Comparative
Photocatalytic Activity. J. Phys. Chem. C 2009, 113, 14159-14164.
27. Huang, W.-C.; Lyu, L.-M.; Yang, Y.-C.; Huang, M. H. Synthesis of Cu2O Nanocrystals from Cubic to Rhombic Dodecahedral Structures and Their Comparative Photocatalytic Activity. J. Am. Chem. Soc. 2012, 134, 1261-1267.
28. Wang, N.; Xu, A.; Ou, P.; Hung, S. F.; Ozden, A.; Lu, Y. R.; Abed, J.; Wang, Z.; Yan, Y.; Sun, M. J.; Xia, Y.; Han, M.; Han, J.; Yao, K.; Wu, F. Y.; Chen, P. H.; Vomiero, A.; Seifitokaldani, A.; Sun, X.; Sinton, D.; Liu, Y.; Sargent, E. H.; Liang, H. Boride-Derived Oxygen-Evolution Catalysts. Nat. Commun. 2021, 12, 6089.
29. Makula, P.; Pacia, M.; Macyk, W. How To Correctly Determine the Band Gap Energy of Modified Semiconductor Photocatalysts Based on UV-Vis Spectra. J. Phys. Chem. Lett. 2018, 9, 6814-6817.
30. Huang, Y.-C.; Wu, S.-H.; Hsiao, C.-H.; Lee, A.-T.; Huang, M. H. Mild Synthesis of Size-Tunable CeO2 Octahedra for Band Gap Variation. Chem. Mater. 2020, 32, 2631-2638.
31. Zoellner, B.; Gordon, E.; Maggard, P. A. A Small Bandgap Semiconductor, P-type MnV2O6, Active for Photocatalytic Hydrogen and Oxygen Production. Dalton Trans. 2017, 46, 10657-10664.