全世界相當重視全球能源危機，且迫切找到危機的解決方案。赤鐵礦有低毒性、地球含量豐富、合適的能階差、低成本的特點，這些使它被視為問題的解答之一。然而赤鐵礦也有若干缺點阻礙著自身的應用，包括表面態、高電子電洞重合率、電子擴散距離短以及產氧反應不佳。

根據我們之前的研究，過度金屬可鈍化赤鐵礦電極表面的表面態，以改善赤鐵礦電極的效率。在本篇研究中接續之前的研究，將表面態已鈍化的赤鐵礦電極做簡單的後熱處理，以期更進一步增進其效能。

Coming up with the solutions to global energy crisis has become an urgent and important issue. Hematite raises one of the possible candidates owing to its low toxicity, earth abundance, suitable bandgap and low cost. However some defects of hematite itself stand in the way of utilization efficient. Such as surface states, high electron-hole recombination rate, short diffusion length and poor oxygen evolution reaction (OER).

Based on our previous studies, using transition metals as passivation agents can deal with surface states of hematite so that the efficiency of hematite can be improved. In this research, we apply simple post heat treatment to surface states passivated hematite electrodes, attempting to further enhance the performance of hematite electrodes.

[1] A. Fujishima, K. Honda, “Electrochemical Photolysis of Water at a Semiconductor Electrode,” Nature, vol. 238, no. 5358, p.37-38, 1972
[2] B. Klahr, S. Gimenez, F. Fabregat-Santiago, J. Bisquert, T. W. Hamann, “Electrochemical and photoelectrochemical investigation of water oxidation with hematite electrodes,” Energy Environ. Sci., vol. 5, no. 6, p. 7626, 2012.
[3] A. Kay, I. Cesar, M. Gratzel, “New benchmark for water photooxidation by nanostructured alpha-Fe2O3 films,” J. Am. Chem. Soc., vol. 128, no. 49, p. 15714-15721, 2006
[4] N. T. Hahn, C. B. Mullins, “Photoelectrochemical Performance of Nanostructured Ti- and Sn-Doped alpha-Fe2O3 Photoanodes,” Chem. Mater., vol. 22, no. 23, p 6474-6482, 2010
[5] K. D. Malviya, H. Dotan, D. Shlenkevich, A. Tsyganok, H. Mor, Avner Rothschild, “Systematic comparison of different dopants in thin film hematite (a-Fe2O3) photoanodes for solar water splitting,” J. Mater. Chem. A, vol. 4, no. 8, p. 3091-3099, 2016
[6] T. Wang, Y. R. Cheng, Y. Y. Wu, C. A. Lin, C. C. Chiang, Y. K. Hsieh, C. F. Wang, C. P. Huang, “Enhanced Photoelectrochemical Water Splitting Efficiency of Hematite Electrodes with Aqueous Metal Ions as in situ Homogenous Surface Passivation Agents,” Phys. Chem. Chem. Phys., vol. 18, no. 42, 2016.
[7] M. Gratzel, “Photoelectrochemical cells,” Nature, vol. 414, no. 6861, p. 338-344, 2001
[8] Y. Li, J. Z. Zhang, “Hydrogen generation from photoelectrochemical water splitting based on nanomaterials,” Laser Photonics Rev., vol. 4, no. 4, p. 517-528, 2010
[9] Y. Lin, S. Zhou, X. H. Liu, S. W. Sheehan, D. J. Wang, “TiO2/TiSi2 Heterostructures for High-Efficiency Photoelectrochemical H2O Splitting,” J Am Chem Soc., vol. 131, no. 8, p. 2772-2773, 2009
[10] Y. C. Ling, G.M. Wang, D. A. Wheeler, J. Z. Zhang, Y. Li, “Sn-Doped Hematite Nanostructures for Photoelectrochemical Water Splitting,” Nano Lett., vol. 11, no. 5, p. 2119-2125, 2011
[11] R. Liu, Y. J. Lin, L. Y. Chou, S. W. Sheehan, W. S. He, F. Zhang, H. J. M. Hou, D. W. Wang, “Water Splitting by Tungsten Oxide Prepared by Atomic Layer Deposition and Decorated with an Oxygen-Evolving Catalyst,” Angew. Chem., Int. Ed., vol. 50, no. 2, p. 499-502, 2011
[12] K.Sivula K, F. Le Formal, M. Gratzel, “WO3-Fe2O3 Photoanodes for Water Splitting: A Host Scaffold, Guest Absorber Approach,” Chem. Mater., vol. 21, no. 13, 2862-2867, 2009
[13] G. M. Wang, X. Y. Yang, F. Qian, J. Z. Zhang, Y. Li, “Double-Sided CdS and CdSe Quantum Dot Co-Sensitized ZnO Nanowire Arrays for Photoelectrochemical Hydrogen Generation,” Nano Lett., vol.10, no. 3, p1088-1092, 2010
[14] J. Hensel, G. M. Wang, Y. Li, J. Z. Zhang, “Synergistic Effect of CdSe Quantum Dot Sensitization and Nitrogen Doping of TiO2 Nanostructures for Photoelectrochemical Solar Hydrogen Generation,” Nano Lett., vol. 10, no. 2, p478-483, 2010
[15] X.Y. Yang, A. Wolcott, G. M. Wang, A. Sobo, R. C. Fitzmorris, F. Qian, J. Z. Zhang, Y. Li, “Nitrogen-Doped ZnO Nanowire Arrays for Photoelectrochemical Water Splitting,” Nano Lett., vol. 9, no. 6, p. 2331-2336, 2009
[16] J. Brillet, M. Gratzel, K. Sivula, “Decoupling Feature Size and Functionality in Solution-Processed, Porous Hematite Electrodes for Solar Water Splitting,” Nano Lett., vol. 10, no. 10, p. 4155-4160, 2010
[17] I. Cesar, A. Kay, J. A. G. Martinez, M. Gratzel, “Translucent thin film Fe2O3 photoanodes for efficient water splitting by sunlight: Nanostructure-directing effect of Si-doping,” J. Am. Chem. Soc., vol. 128, no. 14, p. 4582-4583, 2006
[18] M. Frites, Y. A. Shaban, S. U. M. Khan, “Iron oxide (n-Fe2O3) nanowire films and carbon modified (CM)-n-Fe2O3 thin films for hydrogen production by photosplitting of water,” Int. J. Hydrogen Energy., vol. 35, no. 10, p. 4944-4948, 2010
[19] M. Gaudon, N. Pailhe, J. Majimel, A. Wattiaux, J. Abel, A. Demourgues, “Influence of Sn4+ and Sn4+/Mg2+ doping on structural features and visible absorption properties of alpha-Fe2O3 hematite,” J. Solid State Chem., vol. 183, no. 9, p. 2101-2109, 2010
[20] M. Gratzel, J. Kiwi, C. L. Morrison, R. S. Davidson, A. C. C. Tseung, “Visible-Light-Induced Photodissolution of Alpha-Fe2o3 Powder in the Presence of Chloride Anions,” J. Chem. Soc. Farady Trans. 1., vol 81, p. 1883-1890, 1985
[21] W. B. Ingler, S. U. M. Khan, “Photoresponse of spray pyrolytically synthesized magnesium-doped iron(III) oxide (p-Fe2O3) thin films under solar simulated light illumination,” Thin Solid Films., vol. 461, no. 2, p. 301-308, 2004
[22] W. B. Ingler, S. U. M. Khan, “A self-driven p/n-Fe2O3 tandem photoelectrochemical cell for water splitting,” Electrochem. Solid-State lett., vol. 9, no, 4, p. G144-G146, 2006
[23] S. Kumari, A. P. Singh AP, Sonal, D. Deva, R. Shrivastav, S. Dass, V. R. Satsangi, “Spray pyrolytically deposited nanoporous Ti4+ doped hematite thin films for efficient photoelectrochemical splitting of water,” Int. J. Hydrogen Energy., vol. 35, no. 9, p. 3985-3990, 2010
[24] F. Le Formal, M. Gratzel, K. Sivula, “Controlling Photoactivity in Ultrathin Hematite Films for Solar Water-Splitting,” Adv. Funct. Mater., vol. 20, no. 7, p. 1099-1107, 2010
[25] K. Sivula, R. Zboril, F. Le Formal, R. Robert, A. Weidenkaff, J. Tucek, J. Frydrych, M. Graetzel, “Photoelectrochemical Water Splitting with Mesoporous Hematite Prepared by a Solution-Based Colloidal Approach,” J. Am. Chem. Soc., vol. 132, no. 21, p. 7436-7444, 2010
[26] S. D. Tilley, M. Cornuz, K. Sivula, M. Gratzel, “Light-Induced Water Splitting with Hematite: Improved Nanostructure and Iridium Oxide Catalysis,” Angew. Chem., Int. Ed., vol. 49, no. 36, p. 6405-6408, 2010
[27] H. L. Wang, J. A. Turner, “Characterization of Hematite Thin Films for Photoelectrochemical Water Splitting in a Dual Photoelectrode Device,” J. Electrochem. Soc., vol. 157, no. 11, p. F173-F178, 2010
[28] Y. J. Lin, S. Zhou, S. W. Sheehan, D. W. Wang, “Nanonet-Based Hematite Heteronanostructures for Efficient Solar Water Splitting,” J. Am. Chem. Soc., vol. 133, no. 8, p. 2398-2401, 2011
[29] D. K. Zhong, J. W. Sun, H. Inumaru, D. R. Gamelin, “Solar Water Oxidation by Composite Catalyst/alpha-Fe2O3 Photoanodes,” J. Am. Chem. Soc., vol. 131, no. 17, p. 6086-6087, 2009
[30] I. Cesar, K. Sivula, A. Kay, R. Zboril, M. Graetzel, “Influence of Feature Size, Film Thickness, and Silicon Doping on the Performance of Nanostructured Hematite Photoanodes for Solar Water Splitting,” J. Phys. Chem. C., vol. 113, no. 2, p. 772-782, 2009
[31] N. J. Cherepy, D. B. Liston, J. A. Lovejoy, H. M. Deng, J. Z. Zhang, “Ultrafast studies of photoexcited electron dynamics in gamma- and alpha-Fe2O3 semiconductor nanoparticles,” J. Phys. Chem. B., vol. 102, no. 5, p. 770-776, 1998
[32] M. P. Dareedwards, J. B. Goodenough, A. Hamnett, P. R. Trevellick, “Electrochemistry and Photoelectrochemistry of Iron(III) Oxide,” J. Chem. Soc. Faraday Trans. 1., vol. 79, p. 2027-2041, 1983
[33] K. Sivula, F. Le Formal, M. Gratzel, “Solar Water Splitting: Progress Using Hematite (alpha-Fe2O3) Photoelectrodes,” ChemSusChem, vol. 4, no. 4, p. 432-449, 2011
[34] M. D. Hernandez-Alonso, F. Fresno, S. Suarez, J. M. Coronado, “Development of alternative photocatalysts to TiO2: Challenges and opportunities,” Energy Environ. Sci., vol. 2, no. 12, p. 1231-1257, 2009
[35] K. Maeda, K. Domen, “Photocatalytic Water Splitting: Recent Progress and Future Challenges,” J. Phys. Chem. Lett., vol. 1, no. 18, p. 2655-2661, 2010
[36] A. J. Esswein, D. G. Nocera, “Hydrogen production by molecular photocatalysis,” Chem. Rev., vol. 107, no. 10, p. 4022-4047, 2007
[37] P. J. Boddy, “Oxygen Evolution on Semiconducting TiO2,” J. Electrochem. Soc., vol. 115, no. 2, p. 199-203, 1968
[38] M. Szklarczyk, J. O. Bockris, “Photoelectrochemical Evolution of Hydrogen on Para-Indium Phosphide,” J. Phys. Chem., vol. 88,no. 22, p. 5241-5245, 1984
[39] M. Woodhouse, B. A. Parkinson, “Combinatorial approaches for the identification and optimization of oxide semiconductors for efficient solar photoelectrolysis,” Chem. Soc. Rev., vol. 38, no. 1, p. 197-210, 2009
[40] A. Walsh, S. H. Wei, Y. Yan, M. M. Al-Jassim, J. A. Turner, “Structural, magnetic, and electronic properties of the Co-Fe-Al oxide spinel system: Density-functional theory calculations,” Phys. Rev. B, vol. 76, no.16, p. 165119, 2007
[41] J. Greeley, T. F. Jaramillo, J. Bonde, I. B. Chorkendorff, J. K. Norskov, “Computational high-throughput screening of electrocatalytic materials for hydrogen evolution,” Nat. Mater., vol. 5, no. 11, p. 909-13, 2006
[42] M. Barroso, A. J. Cowan, S. R. Pendlebury, M. Gratzel, D. R. Klug, J. R. Durrant, “The Role of Cobalt Phosphate in Enhancing the Photocatalytic Activity of alpha-Fe2O3 toward Water Oxidation,” J. Am. Chem. Soc., vol. 133, no. 38, p. 14868-14871, 2011
[43] A. Kudo, Y. Miseki, “Heterogeneous photocatalyst materials for water splitting,” Chem. Soc. Rev., vol. 38, no. 1, p. 253-278, 2009
[44] F. E. Osterloh, “Inorganic materials as catalysts for photochemical splitting of water,” Chem. Mater., vol. 20, no. 1, p. 35-54, 2008
[45] A Harriman, I. J. Pickering, J. M. Thomas, P. A. Christensen, “Metal-Oxides as Heterogeneous Catalysts for Oxygen Evolution under Photochemical Conditions,” J. Chem. Soc. Faraday Trans. 1., vol. 84, p. 2795-2806, 1988
[46] J. S. Peng, M. Ye, C. J. Zong, F. Y. Hu, L. T. Feng, X. Y. Wang, Y. F. Wang, C. X. Chen, “Copper-Catalyzed Intramolecular C-N Bond Formation: A Straightforward Synthesis of Benzimidazole Derivatives in Water,” J. Org. Chem., vol. 76, no. 2, p. 716-719, 2011
[47] D. K. Zhong, M. Cornuz, K. Sivula, M. Graetzel, D. R. Gamelin, “Photo-assisted electrodeposition of cobalt-phosphate (Co-Pi) catalyst on hematite photoanodes for solar water oxidation,” Energy Environ. Sci., vol. 4, no. 5, p. 1759-1764, 2011
[48] A. Kleiman-Shwarsctein, Y. S. Hu, G. D. Stucky, E. W. McFarland, “NiFe-oxide electrocatalysts for the oxygen evolution reaction on Ti doped hematite photoelectrodes,” Electrochem Commun., vol. 11, no. 6, p. 1150-1153, 2009
[49] G. L. Elizarova, G. M. Zhidomirov, V. N. Parmon, “Hydroxides of transition metals as artificial catalysts for oxidation of water to dioxygen,” Catal. Today., vol. 58, no. 2-3, p. 71-88, 2000
[50] F. Jiao, H. Frei, “Nanostructured Cobalt Oxide Clusters in Mesoporous Silica as Efficient Oxygen-Evolving Catalysts,” Angew. Chem. Int., Ed., vol. 48, no. 10, p. 1841-1844, 2009
[51] V. Artero, M. Chavarot-Kerlidou, M. Fontecave, “Splitting Water with Cobalt,” Angew. Chem., Int. Ed., vol. 50, no. 32, p. 7238-7266, 2011
[52] Y. Surendranath, M. Dinca, D. G. Nocera, “Electrolyte-Dependent Electrosynthesis and Activity of Cobalt-Based Water Oxidation Catalysts,” J. Am. Chem. Soc., vol. 131, no. 7, p. 2615-2620, 2009
[53] M.W. Kanan, Y. Surendranath, D. G. Nocera, “Cobalt-phosphate oxygen-evolving compound,” Chem. Soc. Rev., vol. 38, no. 1, p. 109-114, 2009
[54] Y. Surendranath, M. W. Kanan, D. G. Nocera, “Mechanistic Studies of the Oxygen Evolution Reaction by a Cobalt-Phosphate Catalyst at Neutral pH,” J. Am. Chem. Soc., vol. 132, no. 46, p. 16501-16509, 2010
[55] M. W. Kanan, J. Yano, Y. Surendranath, M. Dinca, V. K. Yachandra, D. G. Nocera, “Structure and Valency of a Cobalt-Phosphate Water Oxidation Catalyst Determined by in Situ X-ray Spectroscopy,” J. Am. Chem. Soc., vol. 132, no. 39, p. 13692-13701, 2010
[56] J. G. McAlpin, Y. Surendranath, M. Dinca, T.A. Stich, S. A. Stoian, W. H. Casey, D. G. Nocera, R. D. Britt, “EPR Evidence for Co(IV) Species Produced During Water Oxidation at Neutral pH,” J. Am. Chem. Soc., vol. 132, no. 20, p. 6882-6883, 2010
[57] M. Risch, V. Khare, I. Zaharieva, L. Gerencser, P. Chernev, H. Dau, “Cobalt-Oxo Core of a Water-Oxidizing Catalyst Film,” J. Am. Chem. Soc., vol. 131, no. 20, p. 6936-6937, 2009
[58] M. D. Symes, Y. Surendranath, D. A. Lutterman, D. G. Nocera, “Bidirectional and Unidirectional PCET in a Molecular Model of a Cobalt-Based Oxygen-Evolving Catalyst,” J. Am. Chem. Soc., vol. 133, no. 14, p. 5174-5177, 2011
[59] A. J. Esswein, Y. Surendranath, S. Y. Reece, D. G. Nocera, “Highly active cobalt phosphate and borate based oxygen evolving catalysts operating in neutral and natural waters,” Energy Environ. Sci., vol. 4, no. 2, p. 499-504, 2011
[60] E. M. P. Steinmiller, K. S. Choi, “Photochemical deposition of cobalt-based oxygen evolving catalyst on a semiconductor photoanode for solar oxygen production,” Proc. Natl. Acad. Sci. USA., vol. 106, no. 49, p. 20633-20636, 2009
[61] J. A. Seabold, K. S. Choi, “Effect of a Cobalt-Based Oxygen Evolution Catalyst on the Stability and the Selectivity of Photo-Oxidation Reactions of a WO3 Photoanode,” Chem. Mater., vol. 23, no. 5, p. 1105-1112, 2011
[62] K. J. McDonald, K. S. Choi, “Photodeposition of Co-Based Oxygen Evolution Catalysts on alpha-Fe2O3 Photoanodes,” Chem. Mater., vol. 23, p. 7, 1686-1693, 2011
[63] K. L. Hardee, A. J. Bard, “Semiconductor Electrodes X . Photoelectrochemical Behavior of Several Polycrystalline Metal Oxide Electrodes in Aqueous Solutions,” J. Electrochem. Soc., vol. 124, no. 2, p. 215–224, 1977.
[64] J. H. Kennedy, K. W. Frese, “Photooxidation of Water at α-Fe2O3 Electrodes,” J. Electrochem. Soc., vol. 125, p. 709–714, 1978.
[65] A. Kleiman-Shwarsctein, Y. S. Hu, A. J. Forman, G. D. Stucky, E. W. McFarland, “Electrodeposition of α-Fe2O3 doped with Mo or Cr as photoanodes for photocatalytic water splitting,” J. Phys. Chem. C, vol. 112, no. 40, p. 15900–15907, 2008.
[66] P. Zhang, A. Kleiman-Shwarsctein, Y. S. Hu, J. Lefton, S. Sharma, A. J. Forman, E. W. McFarland, “Oriented Ti doped hematite thin film as active photoanodes synthesized by facile APCVD,” Energy Environ. Sci., vol. 4, no. 3, p. 1020–1028, 2011.
[67] Y. S. Hu, A. Kleiman-Shwarsctein, A. J. Forman, D. Hazen, J. N.Park, E. W. McFarland, “Pt-doped α-Fe2O3 thin films active for photoelectrochemical water splitting,” Chem. Mater., vol. 20, no. 12, p. 3803–3805, 2008.
[68] A. G. Tamirat, J. Rick, A. A. Dubale, W. N. Su, B. J. Hwang, “Using hematite for photoelectrochemical water splitting: a review of current progress and challenges,” Nanoscale Horiz., vol. 1, no. 4, p. 243–267, 2016.
[69] J. Y. Zheng, M. J. Kang, G. Song, S. I. Son, S. P. Suh, C. W. Kim, Y. S. Kang, “Morphology evolution of dendritic Fe wire array by electrodeposition, and photoelectrochemical properties of α-Fe2O3 dendritic wire array,” CrystEngComm, vol. 14, no. 20, p. 6957, 2012.
[70] Y. W. Phuan, W. J. Ong, M. N. Chong, J. D. Ocon, “ Prospects of electrochemically synthesized hematite photoanodes for photoelectrochemical water splitting: A review,” J. Phototech. Photobio. C, vol.33, p. 54-82, 2017
[71] R. Franking, L. Li, M. A. Lukowski, F. Meng, Y. Z. Tan, R. J. Hamers, S. Jin, “Facile post-growth doping of nanostructured hematite photoanodes for enhanced photoelectrochemical water oxidation,” Energy Environ. Sci, vol. 6, no. 2, 2013
[72] M. A. Lukowski, S. Jin, “Improved Synthesis and Electrical Properties of Si-Doped alpha-Fe2O3 Nanowires,” J. Phys. Chem. C, vol. 115, no. 25, p. 12388–12395, 2011
[73] F. Le Formal, K. Sivula, M. Gratzel, ” The Transient Photocurrent and Photovoltage Behavior of a Hematite Photoanode under Working Conditions and the Influence of Surface Treatments,” J. Phys. Chem. C, vol. 116, no. 51, p. 26707–26720, 2012
[74] X. Y. Su, W. W. Ju, R. Z. Zhang, C. F. Guo, J. M. Zheng, Y. L. Yong, X. H. Li, ” Bandgap engineering of MoS2/MX2 (MX2 = WS2, MoSe2 and WSe2) heterobilayers subjected to biaxial strain and normal compressive strain,” RSC Adv., vol.6, no. 22, p. 18319-18325, 2016
[75] S. M. Chang, ” Is Surface Doping or Bulk Doping More Beneficial to the Photocatalytic Activity of TiO2,” ACS Symposium Series, vol. 1184, p. 121-131, 2014