臺灣博碩士論文加值系統

本研究探討四氯化鈦(TiCl4)在高濃度硝酸(5 M HNO3)水溶液系統中，鈦離子濃度([Ti4+])及反應溫度對生成二氧化鈦晶相[銳鈦礦(anatase)、板鈦礦(brookite)及金紅石(rutile)]的影響。結果顯示在100 oC下，在我們所探討的[Ti4+]區間內(0.3 - 0.6M)，產物晶相皆為brookite/rutile混相。在70 oC下，當鈦離子濃度為0.3, 0.6及0.8 M時，產物晶相分別為brookite/rutile混相，anatase/brookite/rutile混相及anatase/rutile混相。我們將上述混相樣品與乙醇混合、離心後，可進一步地分離出anatase、brookite、rutile個別的純相二氧化鈦。亞甲基藍光脫色反應測試顯示三種晶相中以brookite催化活性最佳，anatase次之，rutile最差。
我們將anatase、brookite、rutile三種純相二氧化鈦在450 oC下鍛燒30分鐘(同染料敏化太陽能電池及光電催化水分解的電極製備條件)後進行特性鑑定。高解析電子顯微鏡(HRTEM)觀察顯示anatase呈顆粒形貌，brookite呈平板狀，而rutile呈棒狀。N2等溫吸附實驗顯示anatase、brookite及rutile的BET表面積分別為91、76及32 m2/g。紫外光可見光光譜(UV-vis)顯示三種晶相中以rutile光散射能力最佳，brookite次之，anatase最差。
染料敏化太陽能電池測試(模擬太陽光AM 1.5, 100 mW/cm2)顯示在相同的膜厚下，由於anatase電池所吸附染料最多(N719ads = 0.060 μmol cm-2)，故其光電轉換效率最佳(η = 4.26%)，明顯優於brookite電池的2.50% (N719ads = 0.041 μmol cm-2)以及rutile電池的1.55% (N719ads = 0.016 μmol cm-2)。
由於rutile及brookite擁有不錯的光散射能力，我們嘗試以溶膠凝膠(sol-gel)法製得anatase奈米顆粒(SG)作為染料敏化太陽能電池電極活性層(active layer)，探討rutile及brookite作為散射層(scattering layer)的影響。結果顯示塗佈rutile及brookite作為散射層，可使SG電池的光電轉換效率由7.09% 分別大幅提升至8.44% 及9.10%。這是因為brookite除了光散射特性佳可提高光使用率(light- harvesting efficiency)外，也有不錯的染料吸附能力。

光電催化分解水反應測試結果顯示anatase、brookite及rutile純相二氧化鈦電極的光電轉換效率分別為0.43%、0.87% 及0.80%。入射單色光子─電子轉換效率(incident photon-to-current efficiency, IPCE)量測顯示brookite及rutile電極的光使用率明顯優於anatase。我們由光電流隨時間衰退變化求出anatase、brookite及rutile的暫態時間(transient time)分別為0.20、0.71及0.42秒，顯示電子在brookite電極間應有較長的壽命。
我們利用同步輻射中心的原位X光繞射光譜(in-situ XRD)探討硫酸濃度在TiCl4/HNO3水溶液系統中對生成二氧化鈦晶相的影響。結果顯示在此系統中添加硫酸除了可抑制brookite/rutile生成及促進anatase生成之外，改變硫酸濃度亦能控制rutile及anatase生成時間順序。我們利用這種特性成功地製得以anatase作為活性層、rutile作為散射層的染料敏化太陽能電池電極(即anatase早於rutile生成於導電玻璃)，電池光電轉換效率可達4.11%。此一新穎二氧化鈦電極製備方法預期可大幅改善文獻中刮刀成膜(doctor-blade)法所需的多次重覆塗佈鍛燒製程。

In this study, the influences of Ti4+ concentration and reaction temperature on TiO2 phases (anatase, brookite and rutile) formed from hydrolysis of TiCl4 in 5 M HNO3(aq) were investigated. It is found that at the temperature of 100 oC, in the [Ti4+] range between 0.3 and 0.6 M, only brookite/rutile mixed phases form. While at the temperature of 70 oC, as [Ti4+] equals to 0.3, 0.6 and 0.8 M, respectively, brookite/rutile, anatase/brookite/rutile and anatase/rutile mixed phases are obtained. Separation of mixed phases into individual pure anatase, brookite and rutile was achieved via mixing as-synthesized samples with C2H5OH followed by centrifugation. Among them, brookite exhibits the best photocatalytic activity in the photobleaching of methylene blue under 300 nm UV illumination.
Pure anatase, brookite and rutile samples were characterized via various instruments after calcination at 450 oC for 30 min (condition the same as the fabrication of electrode for dye-sensitized solar cell and water splitting). As revealed by HRTEM, the three phases exhibit their distinctive morphologies: nanoparticle for anatase, nanoplate for brookite and nanorod for rutile. The BET surface areas are 91, 76 and 32 m2/g, respectively. UV-vis spectra showed that the scattering abilities are in the order of rutile, brookite and anatase.
Photovoltaic performance of dye-sensitized solar cells made up of anatase, brookite and rutile with the same thickness were measured under AM 1.5 (100 mW/cm2). Due to the superior capability for N719 dye adsorption (N719ads = 0.060 μmol cm-2), anatase-based cell exhibits the highest photoconversion efficiency (η = 4.26%), as compared to those of brookite- (2.50%, N719ads = 0.041 μmol cm-2) and rutile-based (1.55%, N719ads = 0.016 μmol cm-2) cells.
Anatase nanoparticles prepared via sol-gel method (SG) were utilized as active layer and brookite/rutile, due to their better scattering abilities, as scattering layer for DSSC photoanodes. Photoconversion efficiencies were increased from 7.09% without scattering layers to 8.44% and 9.10% with rutile/brookite as scattering layers, respectively. Brookite can not only adsorb more dye but scatter incident light.
Photocatalytic water splitting reaction indicated photoconversion efficiencies of pure anatase-, brookite- and rutile-based working electrodes are 0.43%, 0.87% and 0.80%, respectively. Brookite and rutile exhibit better light-harvesting efficiencies than anatase in incident photon-to-current efficiency (IPCE) measurements. Transient times of anatase, brookite and rutile calculated by photocurrent relaxation with time are 0.20, 0.71 and 0.42 s, respectively, which revealed brookite electrode has the longest electron lifetime than the other two polymorphs.
The effect of H2SO4 concentration on TiO2 phases formed in TiCl4/HNO3(aq) system was studied via in-situ XRD, NSRRC. It is showed that addition of H2SO4 enables the suppression of brookite/rutile and promotion of anatase in this system, and formation orders of anatase and rutile can be well-controlled by adjusting [H2SO4]. The case that anatase emerges before rutile was chosen to fabricate TiO2/TCO electrode. Such bilayer microstructure is adopted to utilize smaller anatase to adsorb more dye and larger rutile particles to scatter incident light. The photoconversion efficiency is 4.11%, and the result demonstrates that this facile process is very promising to fabricate TiO2/TCO electrode for efficient photovoltaic devices.

謝誌…………………………………………………………………………....………I
摘要…………………………………………………………………………………...II
Abstract…………………………………………………………………………....…IV
目錄..............................................................................................................................VI
圖目錄..........................................................................................................................IX
表目錄.......................................................................................................................XIII
第一章 緒論…………………………………………………………………………1
1.1 前言…………………………………………………………………………...1
1.2 二氧化鈦(Titanium Dioxide)簡介……………………………………………2
1.3 板鈦礦(brookite)的文獻回顧與合成方法…………………………………...6
1.4 染料敏化太陽能電池(Dye-sensitized solar cell, DSSC)…………………….9
1.4.1 染料敏化太陽能電池的工作原理與影響因素…………………………10
1.4.2 散射層(Scattering layer)概念的應用及文獻回顧………………………14
1.5 水分解(Water splitting)製氫原理及文獻回顧……………………………...16
1.6 研究動機…………………………………………………………………….20

第二章 實驗方法…………………………………………………………………..21
2.1 藥品與儀器………………………………………………………………….21
2.2 以水解法製備二氧化鈦奈米粒子………………………………………….23
2.3 奈米粒子的鍛燒處理……………………………………………………….23
2.4 以溶膠凝膠法製備二氧化鈦奈米粒子………………..…………………...25
2.5 材料特性分析……………………………………………………………….26
2.5.1 高解析穿透式電子顯微鏡 (HRTEM)…………………………………..26
2.5.2 場發射掃描式電子顯微鏡 (FESEM)…………………………………..26
2.5.3 X-射線繞射光譜 (XRD)………………………………………………26
2.5.4 拉曼光譜 (Raman)………………………………………………………28
2.5.5 氮氣等溫吸附……………………………………………….…………...28
2.5.6 紫外光-可見光吸收光譜 (UV-Vis)……………………………………..28
2.5.7 傅立葉紅外線轉換光譜 (FT-IR)………………………………..………29
2.5.8 X光吸收光譜 (XAS)……………………………………………………29
2.5.9 光致發光光譜 (PL)……………………………………………………...30
2.5.10 原位X-射線繞射光譜 (in-situ XRD)…………………………………31
2.6 亞甲基藍光脫色(photobleaching)…………………………………………..32
2.7 染料敏化太陽能電池與水分解反應……………………………………….35
2.7.1 二氧化鈦光陽極/水分解工作電極之製備…………..…………………35
2.7.2 染料敏化太陽能電池與水分解反應之裝置及電化學測試……………37
2.7.3 染料敏化太陽能電池光陽極之染料吸附量測試....................................52

第三章 結果與討論..................................................................................................54
3.1 奈米二氧化鈦之製備及光催化活性評估………………………………….54
3.1.1 初合成(as-synthesized)產物的鑑定……………………………………..54

3.1.2 初合成產物之亞甲基藍光脫色反應……………………………………64
3.2 鍛燒後(calcined)產物之特性鑑定…………………………….……………71
3.3 染料敏化太陽能電池……………………………………………………….74
3.3.1 三晶相奈米薄膜之染料敏化太陽能電池性能測試結果………………74
3.3.2 開環電壓衰退(OCVD)與電化學阻抗(EIS)測試結果………………….76
3.3.3 散射特性的比較…………………………………………………………79
3.3.4 雙層結構光陽極………………………………………………………....83
3.3.5 入射單色光子-電子轉化效率(IPCE)測試結果...………………………88
3.3.6 活性層與散射層組合之效率最佳化….………………………………...90
3.4 水分解……………………...………………………………………………..92
3.4.1 三晶相奈米薄膜水分解測試結果………………………………………92
3.4.2 三晶相與商用二氧化鈦P25奈米薄膜膜厚之最佳化………………….95
3.4.3 入射單色光子-電子轉化效率測試結果………………………………...98
3.4.4 水分解反應限制步驟的探討與暫態時間(transient time )……………100

第四章 結論...…………………………………………………………………….103

第五章 未來展望…………………………………………………………………105

參考文獻……………………………………………………………………………106

附錄...……………………………………………………………………………….112
A 以原位X光繞射(in-situ XRD)光譜儀研究奈米二氧化鈦之生成機制……112
A.1 硫酸根離子的添加對水解系統的影響………………………………...112
A.2 以水解法沉積染料敏化太陽能電池光陽極薄膜…………………..…...118
B 二氧化鈦三晶相JCPDS圖譜…………………………………………….….123

1.A. Di Paolo, L. Palmisano, “Photocatalytic activity of nanocrystalline TiO2 (brookite, rutile and brookite-based) powders prepared by thermohydrolysis of TiCl4 in aqueous chloride solutions”, Colloids and Surfaces A: Physicochem. Eng. Aspects 317 (2008) 366-376.
2.高濂, 鄭珊, 張青紅, “奈米光觸媒”, 五南出版社 (2004), 台北.
3.A.L. Linsebigler, G. Lu and J.T. Yate. Jr., “Photocatalysis on TiO2 surface: principles, mechanism, and selected results” Chem. Rev. 95 (1995) 735.
4.黃冠群, “含鈦孔洞物質之合成、結構特性與催化反應”, 碩士論文, 國立台灣大學化學系 (2003), 台北.
5.T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino and K. Niihara, “Formation of titanium oxide nanotube”, Langmuir 14 (1998) 3160.
6.T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino and K. Niihara, “Titania nanotubes prepared by chemical processing”, Adv. Mater. 11 (1999) 1307.
7.W.Q. Han, O. Gang, “Fe-doped Trititanate Nanotubes: Formation, Optical and Magnetic Properties, and Catalytic Applications”, J. Phys. Chem. C 111 (2007) 14339-14342.
8.C. Adán, M.-Arias, “Structure and activity of nanosized iron-doped anatase TiO2 catalysts for phenol photocatalytic degradation”, Appl. Catal. B: Environmental 72 (2007) 11-18.
9.N. Asong, M. J. Shultz, “The effect of iron doping on the adsorption of methanol on TiO2 probed by sum freqency generation”, Chem. Phys. 339 (2007) 86-93.
10.劉春艷, “納米光催化及光催化環境淨化材料”, 化學工業出版社 (2008), 北京.
11.A. Pottier, J.P. Jolivet, “Synthesis of brookite TiO2 nanoparticles by thermolysis of TiCl4 in strongly acidic aqueous media”, J. Mater. Chem. 11 (2001) 1116-1121.
12.K.J. Jiang, S. Yanagida, “Dye-sensitized Solar Cell Using Brookite Nanoparticle TiO2 Films as Electrodes”, Chem. Lett. 9 (2002) 872-873.
13.M. Addamo, L. Palmisano, “Preparation and photoactivity of nanostructured anatase, rutile and brookite TiO2 thin films”, Chem. Commun. (2006) 4943-4945.
14.J.G. Li, X.D. Sun, “Anatase, Brookite, and Rutile Nanocrystals via Redox Reactions under Mild Hydrothermal Conditions: Phase-Selective Synthesis and Physicochemical Properties”, J. Phys. Chem. C 111 (2007) 4969-4976.
15.I.N. Kuznetsova, A. Kanaev, “TiO2 pure phase brookite with preferred orientation, synthesized as a sin-coated film”, Mater. Lett. 59 (2005) 3820-3823.
16.T. Nagase, T. Ebina, T. Iwasaki, H. Hayashi, Y. Onodera, M. Chatterjee, “Hydrothermal synthesis of brookite”, Chem. Lett. (1999) 911-912.
17.Y.Q. Zheng, E.W. Shi, S.X. Cui, W.J. Li, X.F. Hu, “ Hydrothermal preparation of nanosized brookite powder”, J. Am. Ceram. Soc. 83 (2000) 10 2634-36.
18.I. Keesmann, “Hydrothermal Synthesis of Brookite”, Z. Anorg. Allg. Chem. 346 (1966) 30-43
19.Q.X. Deng, M.D. Wei, K.M. Wei, “Brookite-type nanotubes”, Chem. Commun. (2008) 3657-3659.
20.張正華, 李陵嵐, 葉楚平, 楊平華, “有機與塑膠太陽能電池”, 五南出版社, (2007), 台北.
21.H. Tsubomura, M. Matsumura, Y. Nomura, T. Amamiya, “Dye sensitised zinc oxide: aqueous electrolyte: platinum photocell”, Nature 261 (1976) 402-403.
22.B. O’Regan, M. Grätzel, “A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films”, Nature 353 (1991) 737-740.
23.Y. Chiba, A. Islam, Y. Watanabe, R. Komiya, N. Koide, L. Y. Han, “Dye-sensitized solar cells with conversion efficiency of 11.1%”, Jpn. J. Appl. Phys. 25 (2006) 638-640.
24.M. Grätzel, “Photoelectrochemical cells”, Nature 414 (2001) 338-344.
25.杉原秀樹, 荒川裕則, “色素増感太陽電池用酸化チタン(The light scattering TiO2 particle for the dye-sensitized solar cell)”, Technical Report (2005).
26.M. Grätzel, “Conversion of sunlight to electric power by nanocrystalline dye-sensitized solar cells”, J. Photochem. Photobio. A 164 (2004) 3-14.
27.N. G. Park, G. Schlichthorl, J. van de Lagemaat, H. M. Cheong, A. Mascarenhas, A. J. Frank, “Dye-sensitized TiO2 solar cells: structural and photoelectrochemical characterization of nanocrystalline electrodes formed from the hydrolysis of TiCl4”, J. Phys. Chem. B 103 (1999) 3308-3314.
28.M. K. Nazeeruddin, R. Humphry-Baker, P. Liska, M. Grätzel﹐“Investigation of sensitizer adsorption and the influence of protons on current and voltage of a dye-sensitized nanocrystalline TiO2 solar cell”, J. Phys. Chem. B 107 (2003) 8981-8987.
29.S. Hore, C. Vetter, A. Hinsch, “Influence of scattering layers on efficiency of dye-sensitized solar cells”, Sol. Energy Mater. & Sol. Cells 90 (2006) 1176-1188.
30.N. M. Lawandy, R. M. Balachandran, A.S.L. Gomes, E. Sauvain, “Laser action in strongly scattering media”, Nature 368 (1994) 436-438.
31.C. J. Barbé, F. Arendse, P. Comte, M. Jirousek, F. Lenzmann, V. Shklover, M. Grätzel, “Nanocrystalline titanium oxide electrodes for photovoltaic applications”, J. Am. Ceram. Soc. 80 (1997) 3157-3171.
32.S. Ito, S. M Zakeeruddin, M. Grätzel, “High-Efficiency Organic-Dye-Sensitized Solar Cells Controlled by Nanocrystalline-TiO2 Electrode Thickness”, Adv. Mater. 18 (2006) 1202-1205.
33.H.J. Koo, Y.J. Kim, N.G. Park, “Nano-embossed Hollow Spherical TiO2 as Bifunctional Material for High-Efficiency Dye-Sensitized Solar Cells”, Adv. Mater. 20 (2008) 195-199.
34.A. Fujishima, K. Honda, “Electrochemical photolysis at a semiconductor electrode”, Nature (1972) 37 238.
35.J. Nowotny, T. Bak, M.K. Nowotny, L.R. Sheppard, “Titanium dioxide for solar-hydrogen I. Functional properties”, Int. J. Hydrogen Energy 32 (2007) 2609-2629.
36.L. R. Sheppard, J. Nowotny, “Materials for photoelectrochemical energy conversion”, Adv. Appl. Cera. 106 (2007) 1–2.
37.S. Khan, M. Al-Sahary, W B Ingler, “Efficient Photochemical Water Splitting by a Chemically Modified n-TiO2”, Science 297 (2002) 2243-2245.
38.G. K. Mor, C. A. Grimes, “Vertically Oriented Ti-Fe-O Nanotube Array Films: Toward a Useful Material Architecture for Solar Spectrum Water Photoelectrolysis”, Nano Lett. 7 (2007) 8.
39.M. Paulose, G. K. Mor, C. A. Grimes, “Visible light photoelectrochemical and water-photoelectrolysis properties of titania nanotube arrays”, J. Photochem. Photobio. A: Chemistry 178 (2006) 8-15.
40.C.J. Lin, W.Y. Yu, Y.T. Lu, S.H. Chien, “Fabrication of opened-end high-aspect-ratio anodic TiO2 nanotube film for photocatalytic and photoelectrocatalytic applications”, Chem. Comm. (2008) 6031-6033.
41.J.H. Lee, Y.S. Yang, “Synthesis of TiO2 nanoparticles with pure brookite at low tempeature by hydrolysis of TiCl4 using HNO3 solution”, J. Mater. Sci. 41 (2006) 557-559.
42.A. Mills, J. Wang, “Photobleaching of methylene blue sensitized by TiO2: an ambiguous system?” Journal of Photochem. Photobio. A: Chemistry 127 (1999) 123.
43.A. Zaban, M. Greenshtein, J. Bisquert, “Determination of the electron lifetime in nanocrystalline dye solar cells by open-circuit voltage decay measurements”, ChemPhysChem 4 (2003) 859-864.
44.J. Bisquert, V. Vyacheslav, S. Vikhrenko, “Interpretation of the time constants measured by kinetic techniques in nanostructured semiconductor electrodes and dye-sensitized solar cells”, J. Phys. Chem. B 108 (2004) 2313-2322.
45.J. Bisquert, A. Zaban, M. Greenshtein, I. Mora-Sero, “Determination of rate constants for charge transfer and the distribution of semiconductor and electrolyte electronic energy levels in dye-sensitized solar cells by open-circuit photovoltage decay method”, J. Am. Chem. Soc. 126 (2004) 13550-13559.
46.F. Fabregat-Santiago, J. García-Cañadas, E. Palomares, J. N. Clifford, S. A. Haque, J. R. Durrant, G. Garcia-Belmonte, J. Bisquert, “The origin of slow electron recombination processes in dye-sensitized solar cells with alumina barrier coatings”, J. Appl. Phys. 96 (2004) 6903-6907.
47.C. J. Lin, W. Y. Yu, S. H. Chien, “Effect of anodic TiO2 powder as additive on electron transport properties in nanocrystalline TiO2 dye-sensitized solar cells”, Appl. Phys. Lett. 91 (2007) 233120.
48.P. M. S. Monk. 『Fundamentals of Electroanalytical Chemistry』 8.2 『Electroanalytical Measurements Involving Impedance』 John Wiley & Sons Ltd. (2001)
49.M. Adachi, M. Sakamoto, J. Jiu, Y. Ogata, S. Isoda, “Determination of parameters of electron transport in dye-sensitized solar cells using electrochemical impedance spectroscopy”, J. Phys. Chem. B 110 (2006) 13872-13880.
50.J. J. Wu, G. R. Chen, H. H. Yang, C. H. Ku, J. Y. Lai, “Effects of dye adsorption on the electron transport properties in ZnO-nanowire dye-sensitized solar cells”, Appl. Phys. Lett. 90 (2007) 213109.
51.L. Y. Han, N. Koide, Y. Chiba, T. Mitate, “Modeling of an equivalent circuit for dye-sensitized solar cells”, Appl. Phys. Lett. 84 (2004) 2433-2435.
52.M. Grätzel, “Mesoscopic solar cells for electricity and hydrogen production from sunlight”, Chem. Lett. 34 (2005) 8-13.
53.A. Hagfeldt, S. Lindquist, “Photoelectrochemical studies of colloidal TiO2 films: The effect of oxygen studied by photocurrent transients”, J. Electroanaly. Chem. 381 (1995) 39-46.
54.M. Grätzel, “Molecular photovoltaics that mimic photosynthesis”, Pure Appl. Chem., 73 (2001) 459-467.
55.S.H. Lim, N. Phonthammachai, T. Liu and T.J. White, “X-ray absorption spectroscopy studies of phase transformations and amorphicity in nanotitania powder and silica-titania core shell photocatalysts”, J. Appl. Cryst. (2008) 41 1009-1018.
56.蕭光宏, “二氧化鈦微結構對染料敏化太陽能電池的影響”, 碩士論文, 國立台灣大學化學系 (2008), 台北.
57.M. Yan, F. Chen and M. Anpo, “Preparation of Controllable Crystalline Titania and Study on the Photocatalytic Properties”, J. Phys. Chem. B 109 (2005) 8673-8678.
58.N.G. Park, A. J. Frank,” Dye-sensitized TiO2 Solar Cells: Structured and Photoelectrochemical Characterization of Nanocrystalline Electrodes Formed from the Hydrolysis of TiCl4”, J. Phys. Chem. B 103 (1999) 3308-3314.
59.T. Watanabe, H. Hayashi and H. Imai, “Low-temperature preparation of dye-sensitized solar cells through crystal growth of anatase titania in aqueous solutions”, Sol. Energy Mater. & Sol. Cells 90 (2006) 640-648
60.K.J. Kim, K. D. Benkstein, and A. J. Frank, “ Characterization of Low-Temperature Annealed TiO2 Films Deposited by Precipitation from Hydrolyzed TiCl4 solutions”, Chem. Mater. 14 (2002) 1042-1047.