Photoelectrochemical water splitting has been intensively studied in recent years for the production of sustainable, carbon-free hydrogen fuels. Since the first solar water splitting revelation using semiconductor titanium dioxide (TiO2) in 1972 by Honda and Fujishima, extensive efforts have been invested into improving the solar-to-hydrogen (STH) conversion efficiency and lower the production cost of photoelectrochemical devices. Various photocatalysts, however, are wide band-gap semiconductors which are active only under UV irradiation, unstable in the electrolyte and inappropriate band edge positions for overall water splitting. Among various water splitting semiconductor electrodes, hematite (α-Fe2O3) is one of few materials that favorably combines several promising properties such as; stability in aqueous solutions, visible-light absorption, non-toxicity, abundance and low cost. With an energy band gap of 2.1 eV, hematite can theoretically reach water oxidation current density as high as 12.6 mA cm-2 under air mass 1.5 global (AM 1.5G) solar irradiation; thereby potentially enabling a maximum solar-to-hydrogen conversion efficiency of 15.5%. However, the overall solar-to-hydrogen efficiency of hematite is limited by several factors such as relatively poor absorption coefficient, very short excited-state lifetime (~10-12 s), poor oxygen evolution reaction kinetics, and a short hole diffusion length (2-4 nm). In this study, to exploit iron oxide as efficient photocatalyst, we have demonstrated various approaches.
First, we present a highly photoactive photoanode for solar water oxidation using three dimensional (3D) urchin-like hematite (α-Fe2O3) nanostructures modified with ultra-thin reduced graphene oxide (rGO). rGO acts as both electron conducting scaffold and surface passivation layer. By virtue of these combined effects, the composite photoanode exhibits 1.47 times higher photocurrent density (1.06 mA cm-2, at 1.23 V vs. reversible hydrogen electrode (RHE)) and two-fold enhancement in the photoconversion efficiency than that of pristine α-Fe2O3. The dual effect of rGO as both electron conducting scaffold and surface passivation layer is further evidenced from the 1.82 and 1.67 fold enhancements in charge separation and charge injection efficiencies at 1.23 and 1V vs. RHE respectively.
Second, we develop an efficient photoanode that can oxidize water at low applied potential, aspired to alleviate one of the major challenges in photoelectrochemical water splitting. Consequently, a codoped (Sn, Zr) α-Fe2O3 photoanode modified with stable and earth abundant nickel oxyhydroxide (NiOOH) co-catalyst is reported. Initially, unintentional gradient monodoped (Sn) α-Fe2O3 photoanode was synthesized at controlled annealing temperature that achieved a photocurrent density of 0.86 mA cm-2 at 1.23 V vs. RHE. Further doping with optimized amount of Zr outperformed the monodoped (Sn) α-Fe2O3 photoanode providing significantly much higher photocurrent density (1.34 mA cm-2). The remarkably improved electrical conductivity and more than three times higher charge carrier density (as evidenced from electrochemical impedance spectroscopy measurements and Mott-Schottky analysis) of the codoped (Sn, Zr) α-Fe2O3 photoanode highlights the importance of codoping. The synergetic effect of codoping (Sn, Zr) led to 1.6 fold enhancement in charge separation efficiency at 1.23 V than that of the monodoped (Sn) α-Fe2O3 photoanode. The NiOOH modified codoped (Sn, Zr) α-Fe2O3 photoanode exhibited drastically lower onset potential (0.58 V) and a photocurrent density of 1.64 mA cm-2 at 1.23 V. Interestingly a 160 mV cathodic shift in photocurrent onset potential was also observed. Concomitant with this, the NiOOH modified codoped (Sn, Zr) α-Fe2O3 photoanode exhibited 1.6 to 9.5 fold enhancement in charge injection efficiency (ηinj) at kinetic control region of 0.7 to 0.9 V compared to unmodified codoped photoanode. Gas evolution measurements also showed that the NiOOH modified codoped α-Fe2O3 photoanode achieved an average Faradaic efficiency of 93%.
Achieving high solar to hydrogen conversion efficiency at the lowest possible applied power is one of the challenges in solar hydrogen production from water splitting. The third and last part of this research is therefore targets on splitting water at lowest applied potential by modifying the surface of nanostructed hematite electrode sequentially with surface passivation layer and cocatalyst. Here, we demonstrate a new sequential surface treatment approach with heavily Sn doped surface passivation layer and NiOOH oxygen evolution catalyst. The Sn4+ surface treatment creates heavily doped Fe2-xSnxO3 surface passivation layer which can robustly inhibit interfacial recombination by passivating the surface states. While the NiOOH catalyst layer greatly enhances the charge transfer process across the passivated electrode/electrolyte interface. By exploiting this approach, the optimized sequentially treated photoanode (Fe2O3/Fe2-xSnxO3/NiOOH) exhibits lowest photocurrent onset potential of 0.49 V vs. RHE with an additional effect on enhancing the saturated photocurrent density as high as 2.4 mA cm-2 V at 1.5 V vs. RHE. Transient photocurrent and impedance spectroscopy measurements further reveal that the combined Fe2-xSnxO3/NiOOH layers reduce interfacial recombination and the charge transfer process across the electrode/electrolyte interface. When the NiOOH was first deposited onto Fe2O3 surface and Sn4+ treatment later as over layer to form Fe2O3/NiOOH/Sn4+ (i.e., reversed surface treatment), 200 mV anodic shift in photocurrent onset potential and 41 % decrease in water oxidation photocurrent (at 1.23 V vs. RHE) were observed. The results are convincing evidences that it is possible to address the problems of surface trap recombination and sluggish catalysis independently by employing surface passivation layers first and catalysts later sequentially.
In summary, the current study show fundamental bulk and surface modifications such as: nanostructuring with various morphologies, enhancing the charge separation through doping and applying conducting scaffolds, improving poor water oxidation kinetics through co-catalysts, improving surface state recombination by applying passivation layers etc. Our results demonstrate the benefits of a noble metal free highly promising photoanode for photoelectrochemical water oxidation.

Photoelectrochemical water splitting has been intensively studied in recent years for the production of sustainable, carbon-free hydrogen fuels. Since the first solar water splitting revelation using semiconductor titanium dioxide (TiO2) in 1972 by Honda and Fujishima, extensive efforts have been invested into improving the solar-to-hydrogen (STH) conversion efficiency and lower the production cost of photoelectrochemical devices. Various photocatalysts, however, are wide band-gap semiconductors which are active only under UV irradiation, unstable in the electrolyte and inappropriate band edge positions for overall water splitting. Among various water splitting semiconductor electrodes, hematite (α-Fe2O3) is one of few materials that favorably combines several promising properties such as; stability in aqueous solutions, visible-light absorption, non-toxicity, abundance and low cost. With an energy band gap of 2.1 eV, hematite can theoretically reach water oxidation current density as high as 12.6 mA cm-2 under air mass 1.5 global (AM 1.5G) solar irradiation; thereby potentially enabling a maximum solar-to-hydrogen conversion efficiency of 15.5%. However, the overall solar-to-hydrogen efficiency of hematite is limited by several factors such as relatively poor absorption coefficient, very short excited-state lifetime (~10-12 s), poor oxygen evolution reaction kinetics, and a short hole diffusion length (2-4 nm). In this study, to exploit iron oxide as efficient photocatalyst, we have demonstrated various approaches.
First, we present a highly photoactive photoanode for solar water oxidation using three dimensional (3D) urchin-like hematite (α-Fe2O3) nanostructures modified with ultra-thin reduced graphene oxide (rGO). rGO acts as both electron conducting scaffold and surface passivation layer. By virtue of these combined effects, the composite photoanode exhibits 1.47 times higher photocurrent density (1.06 mA cm-2, at 1.23 V vs. reversible hydrogen electrode (RHE)) and two-fold enhancement in the photoconversion efficiency than that of pristine α-Fe2O3. The dual effect of rGO as both electron conducting scaffold and surface passivation layer is further evidenced from the 1.82 and 1.67 fold enhancements in charge separation and charge injection efficiencies at 1.23 and 1V vs. RHE respectively.
Second, we develop an efficient photoanode that can oxidize water at low applied potential, aspired to alleviate one of the major challenges in photoelectrochemical water splitting. Consequently, a codoped (Sn, Zr) α-Fe2O3 photoanode modified with stable and earth abundant nickel oxyhydroxide (NiOOH) co-catalyst is reported. Initially, unintentional gradient monodoped (Sn) α-Fe2O3 photoanode was synthesized at controlled annealing temperature that achieved a photocurrent density of 0.86 mA cm-2 at 1.23 V vs. RHE. Further doping with optimized amount of Zr outperformed the monodoped (Sn) α-Fe2O3 photoanode providing significantly much higher photocurrent density (1.34 mA cm-2). The remarkably improved electrical conductivity and more than three times higher charge carrier density (as evidenced from electrochemical impedance spectroscopy measurements and Mott-Schottky analysis) of the codoped (Sn, Zr) α-Fe2O3 photoanode highlights the importance of codoping. The synergetic effect of codoping (Sn, Zr) led to 1.6 fold enhancement in charge separation efficiency at 1.23 V than that of the monodoped (Sn) α-Fe2O3 photoanode. The NiOOH modified codoped (Sn, Zr) α-Fe2O3 photoanode exhibited drastically lower onset potential (0.58 V) and a photocurrent density of 1.64 mA cm-2 at 1.23 V. Interestingly a 160 mV cathodic shift in photocurrent onset potential was also observed. Concomitant with this, the NiOOH modified codoped (Sn, Zr) α-Fe2O3 photoanode exhibited 1.6 to 9.5 fold enhancement in charge injection efficiency (ηinj) at kinetic control region of 0.7 to 0.9 V compared to unmodified codoped photoanode. Gas evolution measurements also showed that the NiOOH modified codoped α-Fe2O3 photoanode achieved an average Faradaic efficiency of 93%.
Achieving high solar to hydrogen conversion efficiency at the lowest possible applied power is one of the challenges in solar hydrogen production from water splitting. The third and last part of this research is therefore targets on splitting water at lowest applied potential by modifying the surface of nanostructed hematite electrode sequentially with surface passivation layer and cocatalyst. Here, we demonstrate a new sequential surface treatment approach with heavily Sn doped surface passivation layer and NiOOH oxygen evolution catalyst. The Sn4+ surface treatment creates heavily doped Fe2-xSnxO3 surface passivation layer which can robustly inhibit interfacial recombination by passivating the surface states. While the NiOOH catalyst layer greatly enhances the charge transfer process across the passivated electrode/electrolyte interface. By exploiting this approach, the optimized sequentially treated photoanode (Fe2O3/Fe2-xSnxO3/NiOOH) exhibits lowest photocurrent onset potential of 0.49 V vs. RHE with an additional effect on enhancing the saturated photocurrent density as high as 2.4 mA cm-2 V at 1.5 V vs. RHE. Transient photocurrent and impedance spectroscopy measurements further reveal that the combined Fe2-xSnxO3/NiOOH layers reduce interfacial recombination and the charge transfer process across the electrode/electrolyte interface. When the NiOOH was first deposited onto Fe2O3 surface and Sn4+ treatment later as over layer to form Fe2O3/NiOOH/Sn4+ (i.e., reversed surface treatment), 200 mV anodic shift in photocurrent onset potential and 41 % decrease in water oxidation photocurrent (at 1.23 V vs. RHE) were observed. The results are convincing evidences that it is possible to address the problems of surface trap recombination and sluggish catalysis independently by employing surface passivation layers first and catalysts later sequentially.
In summary, the current study show fundamental bulk and surface modifications such as: nanostructuring with various morphologies, enhancing the charge separation through doping and applying conducting scaffolds, improving poor water oxidation kinetics through co-catalysts, improving surface state recombination by applying passivation layers etc. Our results demonstrate the benefits of a noble metal free highly promising photoanode for photoelectrochemical water oxidation.

[1]F.F. Abdi, L. Han, A.H.M. Smets, M. Zeman, B. Dam, R. van de Krol, Efficient solar water splitting by enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode, Nat Commun 4 (2013) 1-5.
[2]S. Agarwala, Z.H. Lim, E. Nicholson, G.W. Ho, Probing the morphology-device relation of Fe2O3 nanostructures towards photovoltaic and sensing applications, Nanoscale 4 (2012) 194-205.
[3]A.K. Agegnehu, C.-J. Pan, J. Rick, J.-F. Lee, W.-N. Su, B.-J. Hwang, Enhanced hydrogen generation by cocatalytic Ni and NiO nanoparticles loaded on graphene oxide sheets, Journal of Materials Chemistry 22 (2012) 13849-13854.
[4]B.A. Aragaw, C.-J. Pan, W.-N. Su, H.-M. Chen, J. Rick, B.-J. Hwang, Facile one-pot controlled synthesis of Sn and C codoped single crystal TiO2 nanowire arrays for highly efficient photoelectrochemical water splitting, Applied Catalysis B: Environmental 163 (2015) 478-486.
[5]L. Badia-Bou, E. Mas-Marza, P. Rodenas, E.M. Barea, F. Fabregat-Santiago, S. Gimenez, E. Peris, J. Bisquert, Water Oxidation at Hematite Photoelectrodes with an Iridium-Based Catalyst, The Journal of Physical Chemistry C 117 (2013) 3826-3833.
[6]T. Bak, J. Nowotny, M. Rekas, C.C. Sorrell, Photo-electrochemical hydrogen generation from water using solar energy. Materials-related aspects, International Journal of Hydrogen Energy 27 (2002) 991-1022.
[7]A.J. Bard, A.B. Bocarsly, F.R.F. Fan, E.G. Walton, M.S. Wrighton, The concept of Fermi level pinning at semiconductor/liquid junctions. Consequences for energy conversion efficiency and selection of useful solution redox couples in solar devices, Journal of the American Chemical Society 102 (1980) 3671-3677.
[8]A.J. Bard, M.A. Fox, Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen, Accounts of Chemical Research 28 (1995) 141-145.
[9]M. Barroso, A.J. Cowan, S.R. Pendlebury, M. Grätzel, D.R. Klug, J.R. Durrant, The Role of Cobalt Phosphate in Enhancing the Photocatalytic Activity of α-Fe2O3 toward Water Oxidation, Journal of the American Chemical Society 133 (2011) 14868-14871.
[10]P.S. Bassi, Gurudayal, L.H. Wong, J. Barber, Iron based photoanodes for solar fuel production, Physical Chemistry Chemical Physics 16 (2014) 11834-11842.
[11]D.K. Bediako, B. Lassalle-Kaiser, Y. Surendranath, J. Yano, V.K. Yachandra, D.G. Nocera, Structure–Activity Correlations in a Nickel–Borate Oxygen Evolution Catalyst, Journal of the American Chemical Society 134 (2012) 6801-6809.
[12]N. Beermann, L. Vayssieres, S.E. Lindquist, A. Hagfeldt, Photoelectrochemical Studies of Oriented Nanorod Thin Films of Hematite, Journal of The Electrochemical Society 147 (2000) 2456-2461.
[13]R. Beranek, (Photo)electrochemical Methods for the Determination of the Band Edge Positions of TiO2-Based Nanomaterials, Advances in Physical Chemistry 2011 (2011).
[14]G.G. Bessegato, T.T. Guaraldo, M.V.B. Zanoni, Enhancement of Photoelectrocatalysis Efficiency by Using Nanostructured Electrodes, 2014.
[15]F. Bdker, M.F. Hansen, C.B. Koch, K. Lefmann, S. Mrup, Magnetic properties of hematite nanoparticles, Physical Review B 61 (2000) 6826-6838.
[16]C.D. Bohn, A.K. Agrawal, E.C. Walter, M.D. Vaudin, A.A. Herzing, P.M. Haney, A.A. Talin, V.A. Szalai, Effect of Tin Doping on α-Fe2O3 Photoanodes for Water Splitting, The Journal of Physical Chemistry C 116 (2012) 15290-15296.
[17]J.R. Bolton, S.J. Strickler, J.S. Connolly, Limiting and realizable efficiencies of solar photolysis of water, Nature 316 (1985) 495-500.
[18]D.K. Bora, A. Braun, E.C. Constable, "In rust we trust". Hematite - the prospective inorganic backbone for artificial photosynthesis, Energy & Environmental Science 6 (2013) 407-425.
[19]D.K. Bora, A. Braun, S. Erat, O. Safonova, T. Graule, E.C. Constable, Evolution of structural properties of iron oxide nano particles during temperature treatment from 250 °C–900 °C: X-ray diffraction and Fe K-shell pre-edge X-ray absorption study, Current Applied Physics 12 (2012) 817-825.
[20]F. Boudoire, R. Toth, J. Heier, A. Braun, E.C. Constable, Photonic light trapping in self-organized all-oxide microspheroids impacts photoelectrochemical water splitting, Energy & Environmental Science 7 (2014) 2680-2688.
[21]J. Brillet, M. Grätzel, K. Sivula, Decoupling Feature Size and Functionality in Solution-Processed, Porous Hematite Electrodes for Solar Water Splitting, Nano Letters 10 (2010) 4155-4160.
[22]D. Cao, W. Luo, J. Feng, X. Zhao, Z. Li, Z. Zou, Cathodic shift of onset potential for water oxidation on a Ti4+ doped Fe2O3 photoanode by suppressing the back reaction, Energy & Environmental Science 7 (2014) 752-759.
[23]F. Cardon, W.P. Gomes, On the determination of the flat-band potential of a semiconductor in contact with a metal or an electrolyte from the Mott-Schottky plot, Journal of Physics D: Applied Physics 11 (1978) L63.
[24]I. Cesar, A. Kay, J.A. Gonzalez Martinez, M. Grätzel, Translucent Thin Film Fe2O3 Photoanodes for Efficient Water Splitting by Sunlight:  Nanostructure-Directing Effect of Si-Doping, Journal of the American Chemical Society 128 (2006) 4582-4583.
[25]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, Journal of Physical Chemistry C 113 (2009) 772-782.
[26]I. Cesar, K. Sivula, A. Kay, R. Zboril, M. Grätzel, Influence of Feature Size, Film Thickness, and Silicon Doping on the Performance of Nanostructured Hematite Photoanodes for Solar Water Splitting, The Journal of Physical Chemistry C 113 (2009) 772-782.
[27]H.G. Cha, H.S. Noh, M.J. Kang, Y.S. Kang, Photocatalysis: progress using manganese-doped hematite nanocrystals, New Journal of Chemistry 37 (2013) 4004-4009.
[28]H.F. Chen, G.D. Wei, X. Han, S. Li, P.P. Wang, M. Chubik, A. Gromov, Z.P. Wang, W. Han, Large-scale synthesis of hierarchical alpha-FeOOH flowers by ultrasonic-assisted hydrothermal route, Journal of Materials Science: Materials in Electronics 22 (2011) 252-259.
[29]Z. Chen, T.F. Jaramillo, T.G. Deutsch, A. Kleiman-Shwarsctein, A.J. Forman, N. Gaillard, R. Garland, K. Takanabe, C. Heske, M. Sunkara, E.W. McFarland, K. Domen, E.L. Miller, J.A. Turner, H.N. Dinh, Accelerating materials development for photoelectrochemical hydrogen production: Standards for methods, definitions, and reporting protocols, Journal of Materials Research 25 (2010) 3-16.
[30]W. Cheng, J. He, Z. Sun, Y. Peng, T. Yao, Q. Liu, Y. Jiang, F. Hu, Z. Xie, B. He, S. Wei, Ni-Doped Overlayer Hematite Nanotube: A Highly Photoactive Architecture for Utilization of Visible Light, The Journal of Physical Chemistry C 116 (2012) 24060-24067.
[31]N.J. Cherepy, D.B. Liston, J.A. Lovejoy, H. Deng, J.Z. Zhang, Ultrafast Studies of Photoexcited Electron Dynamics in γ- and α-Fe2O3 Semiconductor Nanoparticles, The Journal of Physical Chemistry B 102 (1998) 770-776.
[32]M. Chirita, I. Grozescu, Fe2O3 – Nanoparticles, Physical Properties and Their Photochemical And Photoelectrochemical Applications Chemical Bulletin of “Politehnica” University of Timisoara Volume 54 (2009) 1-8.
[33]J.-C. Chou, S.-A. Lin, C.-Y. Lee, J.-Y. Gan, Effect of bulk doping and surface-trapped states on water splitting with hematite photoanodes, Journal of Materials Chemistry A 1 (2013) 5908-5914.
[34]S. Choudhary, S. Upadhyay, P. Kumar, N. Singh, V.R. Satsangi, R. Shrivastav, S. Dass, Nanostructured bilayered thin films in photoelectrochemical water splitting – A review, International Journal of Hydrogen Energy 37 (2012) 18713-18730.
[35]R.M. Cornell, U. Schwertmann, Characterization, The Iron Oxides, Wiley-VCH Verlag GmbH & Co. KGaA, 2004, pp. 139-183.
[36]R.M. Cornell, U. Schwertmann, Crystal Structure, The Iron Oxides, Wiley-VCH Verlag GmbH & Co. KGaA, 2004, pp. 9-38.
[37]M. Cornuz, M. Grätzel, K. Sivula, Preferential Orientation in Hematite Films for Solar Hydrogen Production via Water Splitting, Chemical Vapor Deposition 16 (2010) 291-295.
[38]C.Y. Cummings, F. Marken, L.M. Peter, K.G. Upul Wijayantha, A.A. Tahir, New Insights into Water Splitting at Mesoporous α-Fe2O3 Films: A Study by Modulated Transmittance and Impedance Spectroscopies, Journal of the American Chemical Society 134 (2011) 1228-1234.
[39]S.K. Cushing, J. Li, F. Meng, T.R. Senty, S. Suri, M. Zhi, M. Li, A.D. Bristow, N. Wu, Photocatalytic Activity Enhanced by Plasmonic Resonant Energy Transfer from Metal to Semiconductor, Journal of the American Chemical Society 134 (2012) 15033-15041.
[40]D.S. Dalavi, R.S. Devan, R.S. Patil, Y.-R. Ma, M.-G. Kang, J.-H. Kim, P.S. Patil, Electrochromic properties of dandelion flower like nickel oxide thin films, Journal of Materials Chemistry A 1 (2013) 1035-1039.
[41]R. De Gryse, W.P. Gomes, F. Cardon, J. Vennik, On the Interpretation of Mott‐Schottky Plots Determined at Semiconductor/Electrolyte Systems, Journal of The Electrochemical Society 122 (1975) 711-712.
[42]J. Deng, X. Lv, J. Gao, A. Pu, M. Li, X. Sun, J. Zhong, Facile synthesis of carbon-coated hematite nanostructures for solar water splitting, Energy & Environmental Science 6 (2013) 1965-1970.
[43]J. Deng, J. Zhong, A. Pu, D. Zhang, M. Li, X. Sun, S.-T. Lee, Ti-doped hematite nanostructures for solar water splitting with high efficiency, Journal of Applied Physics 112 (2012) 084312.
[44]X. Deng, H. Tüysüz, Cobalt-Oxide-Based Materials as Water Oxidation Catalyst: Recent Progress and Challenges, ACS Catalysis 4 (2014) 3701-3714.
[45]M. Dincă, Y. Surendranath, D.G. Nocera, Nickel-borate oxygen-evolving catalyst that functions under benign conditions, Proceedings of the National Academy of Sciences 107 (2010) 10337-10341.
[46]H. Dotan, O. Kfir, E. Sharlin, O. Blank, M. Gross, I. Dumchin, G. Ankonina, A. Rothschild, Resonant light trapping in ultrathin films for water splitting, Nature Materials 12 (2013) 158-164.
[47]H. Dotan, K. Sivula, M. Gratzel, A. Rothschild, S.C. Warren, Probing the photoelectrochemical properties of hematite ([small alpha]-Fe2O3) electrodes using hydrogen peroxide as a hole scavenger, Energy & Environmental Science 4 (2011) 958-964.
[48]C. Du, X. Yang, M.T. Mayer, H. Hoyt, J. Xie, G. McMahon, G. Bischoping, D. Wang, Hematite-Based Water Splitting with Low Turn-On Voltages, Angewandte Chemie International Edition 52 (2013) 12692-12695.
[49]A.A. Dubale, W.-N. Su, A.G. Tamirat, C.-J. Pan, B.A. Aragaw, H.-M. Chen, C.-H. Chen, B.-J. Hwang, The synergetic effect of graphene on Cu2O nanowire arrays as a highly efficient hydrogen evolution photocathode in water splitting, Journal of Materials Chemistry A 2 (2014) 18383-18397.
[50]A.A. Dubale, W.-n. Su, A.G. Tamirat, C.-J. Pan, B.A. Aragaw, H.-M. Chen, C.-H. Chen, B.J. Hwang, Synergetic effect of graphene on Cu2O nanowire arrays as highly efficient hydrogen evolution photocathode in water splitting, Journal of Materials Chemistry A (2014).
[51]A. Duret, M. Grätzel, Visible Light-Induced Water Oxidation on Mesoscopic α-Fe2O3 Films Made by Ultrasonic Spray Pyrolysis, The Journal of Physical Chemistry B 109 (2005) 17184-17191.
[52]N. Dzade, A. Roldan, N. de Leeuw, A Density Functional Theory Study of the Adsorption of Benzene on Hematite (α-Fe2O3) Surfaces, Minerals 4 (2014) 89-115.
[53]L.C.C. Ferraz, W.M. Carvalho, D. Criado, F.L. Souza, Vertically Oriented Iron Oxide Films Produced by Hydrothermal Process: Effect of Thermal Treatment on the Physical Chemical Properties, ACS Applied Materials & Interfaces 4 (2012) 5515-5523.
[54]R. Franking, L. Li, M.A. Lukowski, F. Meng, Y. Tan, R.J. Hamers, S. Jin, Facile post-growth doping of nanostructured hematite photoanodes for enhanced photoelectrochemical water oxidation, Energy & Environmental Science 6 (2013) 500-512.
[55]L. Fu, H. Yu, Y. Li, C. Zhang, X. Wang, Z. Shao, B. Yi, Ethylene glycol adjusted nanorod hematite film for active photoelectrochemical water splitting, Physical Chemistry Chemical Physics 16 (2014) 4284-4290.
[56]Z. Fu, T. Jiang, L. Zhang, B. Liu, D. Wang, L. Wang, T. Xie, Surface treatment with Al3+on a Ti-doped [small alpha]-Fe2O3 nanorod array photoanode for efficient photoelectrochemical water splitting, Journal of Materials Chemistry A 2 (2014) 13705-13712.
[57]A. Fujishima, K. Honda, Electrochemical Photolysis of Water at a Semiconductor Electrode, Nature 238 (1972) 37-38.
[58]H. Gao, C. Liu, H.E. Jeong, P. Yang, Plasmon-Enhanced Photocatalytic Activity of Iron Oxide on Gold Nanopillars, ACS Nano 6 (2011) 234-240.
[59]M. Gaudon, N. Pailhé, J. Majimel, A. Wattiaux, J. Abel, A. Demourgues, Influence of Sn4+ and Sn4+/Mg2+ doping on structural features and visible absorption properties of α-Fe2O3 hematite, Journal of Solid State Chemistry 183 (2010) 2101-2109.
[60]K. Gelderman, L. Lee, S.W. Donne, Flat-Band Potential of a Semiconductor: Using the Mott–Schottky Equation, Journal of Chemical Education 84 (2007) 685.
[61]G. Giovannetti, P.A. Khomyakov, G. Brocks, V.M. Karpan, J. van den Brink, P.J. Kelly, Doping Graphene with Metal Contacts, Physical Review Letters 101 (2008) 026803.
[62]J.A. Glasscock, P.R.F. Barnes, I.C. Plumb, N. Savvides, Enhancement of Photoelectrochemical Hydrogen Production from Hematite Thin Films by the Introduction of Ti and Si, The Journal of Physical Chemistry C 111 (2007) 16477-16488.
[63]R.H. Gonçalves, B.H.R. Lima, E.R. Leite, Magnetite Colloidal Nanocrystals: A Facile Pathway To Prepare Mesoporous Hematite Thin Films for Photoelectrochemical Water Splitting, Journal of the American Chemical Society 133 (2011) 6012-6019.
[64]N.T. Hahn, C.B. Mullins, Photoelectrochemical Performance of Nanostructured Ti- and Sn-Doped α-Fe2O3 Photoanodes, Chemistry of Materials 22 (2010) 6474-6482.
[65]J. Han, X. Zong, Z. Wang, C. Li, A hematite photoanode with gradient structure shows an unprecedentedly low onset potential for photoelectrochemical water oxidation, Physical Chemistry Chemical Physics 16 (2014) 23544-23548.
[66]K.L. Hardee, A.J. Bard1, Semiconductor Electrodes V . The Application of Chemically Vapor Deposited Iron Oxide Films to Photosensitized Electrolysis, J. Electrochem. Soc. 123 (1976) 1024-1026.
[67]K.L. Hardee, A.J. Bard, Semiconductor Electrodes: V . The Application of Chemically Vapor Deposited Iron Oxide Films to Photosensitized Electrolysis, Journal of The Electrochemical Society 123 (1976) 1024-1026.
[68]L. He, L. Jing, Y. Luan, L. Wang, H. Fu, Enhanced Visible Activities of α-Fe2O3 by Coupling N-Doped Graphene and Mechanism Insight, ACS Catalysis 4 (2014) 990-998.
[69]Y.P. He, Y.M. Miao, C.R. Li, S.Q. Wang, L. Cao, S.S. Xie, G.Z. Yang, B.S. Zou, C. Burda, Size and structure effect on optical transitions of iron oxide nanocrystals, Physical Review B 71 (2005) 125411.
[70]T. Hisatomi, J. Kubota, K. Domen, Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting, Chemical Society Reviews 43 (2014) 7520-7535.
[71]T. Hisatomi, F. Le Formal, M. Cornuz, J. Brillet, N. Tetreault, K. Sivula, M. Gratzel, Cathodic shift in onset potential of solar oxygen evolution on hematite by 13-group oxide overlayers, Energy & Environmental Science 4 (2011) 2512-2515.
[72]Y.-R. Hong, Z. Liu, S.F.B.S.A. Al-Bukhari, C.J.J. Lee, D.L. Yung, D. Chi, T.S.A. Hor, Effect of oxygen evolution catalysts on hematite nanorods for solar water oxidation, Chemical Communications 47 (2011) 10653-10655.
[73]Y. Hou, F. Zuo, A. Dagg, P. Feng, Visible Light-Driven α‑Fe2O3 Nanorod/Graphene/BiV1−xMoxO4 Core/Shell Heterojunction Array for Efficient Photoelectrochemical Water Splitting, Nano Letters 12 (2012) 6464−6473.
[74]Y. Hou, F. Zuo, A. Dagg, P. Feng, A Three-Dimensional Branched Cobalt-Doped α-Fe2O3 Nanorod/MgFe2O4 Heterojunction Array as a Flexible Photoanode for Efficient Photoelectrochemical Water Oxidation, Angewandte Chemie International Edition 52 (2013) 1248-1252.
[75]Y. Hou, F. Zuo, A. Dagg, P. Feng, A Three-Dimensional Branched Cobalt-Doped α-Fe2O3 Nanorod/MgFe2O4 Heterojunction Array as a Flexible Photoanode for Efficient Photoelectrochemical Water Oxidation, Angewandte Chemie 125 (2013) 1286-1290.
[76]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, Chemistry of Materials 20 (2008) 3803-3805.
[77]Y.-S. Hu, A. Kleiman-Shwarsctein, G.D. Stucky, E.W. McFarland, Improved photoelectrochemical performance of Ti-doped [small alpha]-Fe2O3 thin films by surface modification with fluoride, Chemical Communications (2009) 2652-2654.
[78]A. Iwase, Y.H. Ng, Y. Ishiguro, A. Kudo, R. Amal, Reduced Graphene Oxide as a Solid-State Electron Mediator in Z-Scheme Photocatalytic Water Splitting under Visible Light, Journal of the American Chemical Society 133 (2011) 11054-11057.
[79]J.W. Jang, C. Du, Y. Ye, Y. Lin, X. Yao, J. Thorne, E. Liu, G. McMahon, J. Zhu, A. Javey, J. Guo, D. Wang, Enabling unassisted solar water splitting by iron oxide and silicon, Nat Commun 6 (2015) 7447.
[80]L. Ji, M.D. McDaniel, S. Wang, A.B. Posadas, X. Li, H. Huang, J.C. Lee, A.A. Demkov, A.J. Bard, J.G. Ekerdt, E.T. Yu, A silicon-based photocathode for water reduction with an epitaxial SrTiO3 protection layer and a nanostructured catalyst, Nat Nano advance online publication (2014).
[81]Y. Jiang, H. Yuan, H. Chen, Enhanced visible light photocatalytic activity of Cu2O via cationic-anionic passivated codoping, Physical Chemistry Chemical Physics 17 (2015) 630-637.
[82]C. Jorand Sartoretti, M. Ulmann, B.D. Alexander, J. Augustynski, A. Weidenkaff, Photoelectrochemical oxidation of water at transparent ferric oxide film electrodes, Chemical Physics Letters 376 (2003) 194-200.
[83]M.W. Kanan, J. Yano, Y. Surendranath, M. Dincă, V.K. Yachandra, D.G. Nocera, Structure and Valency of a Cobalt−Phosphate Water Oxidation Catalyst Determined by in Situ X-ray Spectroscopy, Journal of the American Chemical Society 132 (2010) 13692-13701.
[84]M.J. Katz, S.C. Riha, N.C. Jeong, A.B.F. Martinson, O.K. Farha, J.T. Hupp, Toward solar fuels: Water splitting with sunlight and “rust”?, Coordination Chemistry Reviews 256 (2012) 2521-2529.
[85]A. Kay, I. Cesar, M. Grätzel, New Benchmark for Water Photooxidation by Nanostructured α-Fe2O3 Films, Journal of the American Chemical Society 128 (2006) 15714-15721.
[86]K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, The Optical Properties of Metal Nanoparticles:  The Influence of Size, Shape, and Dielectric Environment, The Journal of Physical Chemistry B 107 (2003) 668-677.
[87]M.J. Kenney, M. Gong, Y. Li, J.Z. Wu, J. Feng, M. Lanza, H. Dai, High-Performance Silicon Photoanodes Passivated with Ultrathin Nickel Films for Water Oxidation, Science 342 (2013) 836-840.
[88]S.U.M. Khan, T. Sultana, Photoresponse of n-TiO2 thin film and nanowire electrodes, Solar Energy Materials and Solar Cells 76 (2003) 211-221.
[89]J.G. Kim, K.H. Han, C.H.L. and, J.Y. Jeong, Crystallographic and Magnetic Properties of Nanostructured Hematite Synthesized by the Sol-Gel Process, Journal of the Korean Physical Society 38 (2001) 798-802.
[90]J.Y. Kim, H. Jun, S.J. Hong, H.G. Kim, J.S. Lee, Charge transfer in iron oxide photoanode modified with carbon nanotubes for photoelectrochemical water oxidation: An electrochemical impedance study, International Journal of Hydrogen Energy 36 (2011) 9462-9468.
[91]J.Y. Kim, G. Magesh, D.H. Youn, J.-W. Jang, J. Kubota, K. Domen, J.S. Lee, Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting, Sci. Rep. 3 (2013).
[92]J.Y. Kim, G. Magesh, D.H. Youn, J.-W. Jang, J. Kubota, K. Domen, J.S. Lee, Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting, Scientific Reports 3 (2013) 1-8.
[93]K. Kim, M.-J. Kim, S.-I. Kim, J.-H. Jang, Towards Visible Light Hydrogen Generation: Quantum Dot-Sensitization via Efficient Light Harvesting of Hybrid-TiO2, Sci. Rep. 3 (2013).
[94]T.W. Kim, K.-S. Choi, Nanoporous BiVO4 Photoanodes with Dual-Layer Oxygen Evolution Catalysts for Solar Water Splitting, Science 343 (2014) 990-994.
[95]B. Klahr, S. Gimenez, F. Fabregat-Santiago, J. Bisquert, T.W. Hamann, Electrochemical and photoelectrochemical investigation of water oxidation with hematite electrodes, Energy & Environmental Science 5 (2012) 7626-7636.
[96]B. Klahr, S. Gimenez, F. Fabregat-Santiago, J. Bisquert, T.W. Hamann, Photoelectrochemical and Impedance Spectroscopic Investigation of Water Oxidation with “Co–Pi”-Coated Hematite Electrodes, Journal of the American Chemical Society 134 (2012) 16693-16700.
[97]B. Klahr, S. Gimenez, F. Fabregat-Santiago, T. Hamann, J. Bisquert, Water Oxidation at Hematite Photoelectrodes: The Role of Surface States, Journal of the American Chemical Society 134 (2012) 4294-4302.
[98]B. Klahr, T. Hamann, Water Oxidation on Hematite Photoelectrodes: Insight into the Nature of Surface States through In Situ Spectroelectrochemistry, The Journal of Physical Chemistry C 118 (2014) 10393-10399.
[99]B.M. Klahr, T.W. Hamann, Current and Voltage Limiting Processes in Thin Film Hematite Electrodes, The Journal of Physical Chemistry C 115 (2011) 8393-8399.
[100]B.M. Klahr, T.W. Hamann, Voltage dependent photocurrent of thin film hematite electrodes, Applied Physics Letters 99 (2011) 063508.
[101]H.P. Klug, L.E. Alexander, X-ray diffraction procedures for polycrystalline and amorphous materials X-Ray Spectrometry 4 (1975) A18-A18.
[102]S. Kment, Z. Hubicka, J. Krysa, D. Sekora, M. Zlamal, J. Olejnicek, M. Cada, P. Ksirova, Z. Remes, P. Schmuki, E. Schubert, R. Zboril, On the improvement of PEC activity of hematite thin films deposited by high-power pulsed magnetron sputtering method, Applied Catalysis B: Environmental 165 (2015) 344-350.
[103]P. Kumar, P. Sharma, R. Shrivastav, S. Dass, V.R. Satsangi, Electrodeposited zirconium-doped α-Fe2O3 thin film for photoelectrochemical water splitting, International Journal of Hydrogen Energy 36 (2011) 2777-2784.
[104]A. Kushwaha, M. Aslam, Defect controlled water splitting characteristics of gold nanoparticle functionalized ZnO nanowire films, RSC Advances 4 (2014) 20955-20963.
[105]J.C. Launay, G. Horowitz, Crystal growth and photoelectrochemical study of Zr-doped α-Fe2O3 single crystal, Journal of Crystal Growth 57 (1982) 118-124.
[106]F. Le Formal, K. Sivula, M. Grätzel, The Transient Photocurrent and Photovoltage Behavior of a Hematite Photoanode under Working Conditions and the Influence of Surface Treatments, The Journal of Physical Chemistry C 116 (2012) 26707-26720.
[107]F. Le Formal, N. Tetreault, M. Cornuz, T. Moehl, M. Gratzel, K. Sivula, Passivating surface states on water splitting hematite photoanodes with alumina overlayers, Chemical Science 2 (2011) 737-743.
[108]J. Li, S.K. Cushing, P. Zheng, F. Meng, D. Chu, N. Wu, Plasmon-induced photonic and energy-transfer enhancement of solar water splitting by a hematite nanorod array, Nat Commun 4 (2013).
[109]J. Li, F. Meng, S. Suri, W. Ding, F. Huang, N. Wu, Photoelectrochemical performance enhanced by a nickel oxide-hematite p-n junction photoanode, Chemical Communications 48 (2012) 8213-8215.
[110]J. Li, Y. Qiu, Z. Wei, Q. Lin, Q. Zhang, K. Yan, H. Chen, S. Xiao, Z. Fan, S. Yang, A three-dimensional hexagonal fluorine-doped tin oxide nanocone array: a superior light harvesting electrode for high performance photoelectrochemical water splitting, Energy & Environmental Science 7 (2014) 3651-3658.
[111]L. Li, P.A. Salvador, G.S. Rohrer, Photocatalysts with internal electric fields, Nanoscale 6 (2014) 24-42.
[112]L. Li, Y. Yu, F. Meng, Y. Tan, R.J. Hamers, S. Jin, Facile Solution Synthesis of α-FeF3•3H2O Nanowires and Their Conversion to α-Fe2O3 Nanowires for Photoelectrochemical Application, Nano Letters 12 (2012) 724-731.
[113]M. Li, J. Deng, A. Pu, P. Zhang, H. Zhang, J. Gao, Y. Hao, J. Zhong, X. Sun, Hydrogen-treated hematite nanostructures with low onset potential for highly efficient solar water oxidation, Journal of Materials Chemistry A 2 (2014) 6727-6733.
[114]Y.-F. Li, A. Selloni, Mechanism and Activity of Water Oxidation on Selected Surfaces of Pure and Fe-Doped NiOx, ACS Catalysis 4 (2014) 1148-1153.
[115]P. Liao, E.A. Carter, Hole transport in pure and doped hematite, Journal of Applied Physics 112 (2012) -.
[116]P. Liao, M.C. Toroker, E.A. Carter, Electron Transport in Pure and Doped Hematite, Nano Letters 11 (2011) 1775-1781.
[117]F. Lin, D. Wang, Z. Jiang, Y. Ma, J. Li, R. Li, C. Li, Photocatalytic oxidation of thiophene on BiVO4 with dual co-catalysts Pt and RuO2 under visible light irradiation using molecular oxygen as oxidant, Energy & Environmental Science 5 (2012) 6400-6406.
[118]Y. Lin, Y. Xu, M.T. Mayer, Z.I. Simpson, G. McMahon, S. Zhou, D. Wang, Growth of p-Type Hematite by Atomic Layer Deposition and Its Utilization for Improved Solar Water Splitting, Journal of the American Chemical Society 134 (2012) 5508-5511.
[119]Y. Lin, G. Yuan, R. Liu, S. Zhou, S.W. Sheehan, D. Wang, Semiconductor nanostructure-based photoelectrochemical water splitting: A brief review, Chemical Physics Letters 507 (2011) 209-215.
[120]Y. Lin, S. Zhou, X. Liu, S. Sheehan, D. Wang, TiO2/TiSi2 Heterostructures for High-Efficiency Photoelectrochemical H2O Splitting, Journal of the American Chemical Society 131 (2009) 2772-2773.
[121]Y. Lin, S. Zhou, S.W. Sheehan, D. Wang, Nanonet-Based Hematite Heteronanostructures for Efficient Solar Water Splitting, Journal of the American Chemical Society 133 (2011) 2398-2401.
[122]Y. Ling, G. Wang, D.A. Wheeler, J.Z. Zhang, Y. Li, Sn-Doped Hematite Nanostructures for Photoelectrochemical Water Splitting, Nano Letters 11 (2011) 2119-2125.
[123]S. Linic, P. Christopher, D.B. Ingram, Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy, Nat Mater 10 (2011) 911-921.
[124]J. Liu, Y.Y. Cai, Z.F. Tian, G.S. Ruan, Y.X. Ye, C.H. Liang, G.S. Shao, Highly oriented Ge-doped hematite nanosheet arrays for photoelectrochemical water oxidation, Nano Energy 9 (2014) 282-290.
[125]R. Liu, Z. Zheng, J. Spurgeon, X. Yang, Enhanced photoelectrochemical water-splitting performance of semiconductors by surface passivation layers, Energy & Environmental Science 7 (2014) 2504-2517.
[126]Y.L. Lo, B.J. Hwang, In Situ Raman Studies on Cathodically Deposited Nickel Hydroxide Films and Electroless Ni−P Electrodes in 1 M KOH Solution, Langmuir 14 (1998) 944-950.
[127]M.W. Louie, A.T. Bell, An Investigation of Thin-Film Ni–Fe Oxide Catalysts for the Electrochemical Evolution of Oxygen, Journal of the American Chemical Society 135 (2013) 12329-12337.
[128]J. Lu, J.-x. Yang, J. Wang, A. Lim, S. Wang, K.P. Loh, One-Pot Synthesis of Fluorescent Carbon Nanoribbons, Nanoparticles, and Graphene by the Exfoliation of Graphite in Ionic Liquids, ACS Nano 3 (2009) 2367-2375.
[129]M.A. Lukowski, S. Jin, Improved Synthesis and Electrical Properties of Si-Doped α-Fe2O3 Nanowires, The Journal of Physical Chemistry C 115 (2011) 12388-12395.
[130]W. Luo, Z. Li, T. Yu, Z. Zou, Effects of Surface Electrochemical Pretreatment on the Photoelectrochemical Performance of Mo-Doped BiVO4, The Journal of Physical Chemistry C 116 (2012) 5076-5081.
[131]L.A. Marusak, R. Messier, W.B. White, Optical absorption spectrum of hematite, αFe2O3 near IR to UV, Journal of Physics and Chemistry of Solids 41 (1980) 981-984.
[132]M.T. Mayer, C. Du, D. Wang, Hematite/Si Nanowire Dual-Absorber System for Photoelectrochemical Water Splitting at Low Applied Potentials, Journal of the American Chemical Society 134 (2012) 12406-12409.
[133]M.T. Mayer, Y. Lin, G. Yuan, D. Wang, Forming Heterojunctions at the Nanoscale for Improved Photoelectrochemical Water Splitting by Semiconductor Materials: Case Studies on Hematite, Accounts of Chemical Research 46 (2013) 1558-1566.
[134]J.G. McAlpin, Y. Surendranath, M. Dincǎ, 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, Journal of the American Chemical Society 132 (2010) 6882-6883.
[135]K.J. McDonald, K.-S. Choi, Synthesis and Photoelectrochemical Properties of Fe2O3/ZnFe2O4 Composite Photoanodes for Use in Solar Water Oxidation, Chemistry of Materials 23 (2011) 4863-4869.
[136]F. Meng, J. Li, S.K. Cushing, J. Bright, M. Zhi, J.D. Rowley, Z. Hong, A. Manivannan, A.D. Bristow, N. Wu, Photocatalytic Water Oxidation by Hematite/Reduced Graphene Oxide Composites, ACS Catalysis 3 (2013) 746-751.
[137]X. Meng, G. Qin, W.A. Goddard, S. Li, H. Pan, X. Wen, Y. Qin, L. Zuo, Theoretical Understanding of Enhanced Photoelectrochemical Catalytic Activity of Sn-Doped Hematite: Anisotropic Catalysis and Effects of Morin Transition and Sn Doping, The Journal of Physical Chemistry C 117 (2013) 3779-3784.
[138]X.Y. Meng, G.W. Qin, S. Li, X.H. Wen, Y.P. Ren, W.L. Pei, L. Zuo, Enhanced photoelectrochemical activity for Cu and Ti doped hematite: The first principles calculations, Applied Physics Letters 98 (2011) 112104.
[139]C. Miao, S. Ji, G. Xu, G. Liu, L. Zhang, C. Ye, Micro-Nano-Structured Fe2O3:Ti/ZnFe2O4 Heterojunction Films for Water Oxidation, ACS Applied Materials & Interfaces 4 (2012) 4428-4433.
[140]N. Mirbagheri, D. Wang, C. Peng, J. Wang, Q. Huang, C. Fan, E.E. Ferapontova, Visible Light Driven Photoelectrochemical Water Oxidation by Zn- and Ti-Doped Hematite Nanostructures, ACS Catalysis 4 (2014) 2006-2015.
[141]S.K. Mohapatra, S.E. John, S. Banerjee, M. Misra, Water Photooxidation by Smooth and Ultrathin α-Fe2O3 Nanotube Arrays, Chemistry of Materials 21 (2009) 3048-3055.
[142]F. Morin, Electrical Properties of α-Fe2O3 and α-Fe2O3 Containing Titanium, Physical Review 83 (1951) 1005-1010.
[143]R. Morrish, M. Rahman, J.M.D. MacElroy, C.A. Wolden, Activation of Hematite Nanorod Arrays for Photoelectrochemical Water Splitting, ChemSusChem 4 (2011) 474-479.
[144]A.C. Nielander, M.J. Bierman, N. Petrone, N.C. Strandwitz, S. Ardo, F. Yang, J. Hone, N.S. Lewis, Photoelectrochemical Behavior of n-Type Si(111) Electrodes Coated With a Single Layer of Graphene, Journal of the American Chemical Society 135 (2013) 17246-17249.
[145]F.E. Osterloh, Inorganic nanostructures for photoelectrochemical and photocatalytic water splitting, Chemical Society Reviews 42 (2013) 2294-2320.
[146]H. Paul, D. Mohanta, Hydrazine reduced exfoliated graphene/graphene oxide layers and magnetoconductance measurements of Ge-supported graphene layers, Applied Physics A 103 (2011) 395-402.
[147]A. Pu, J. Deng, M. Li, J. Gao, H. Zhang, Y. Hao, J. Zhong, X. Sun, Coupling Ti-doping and oxygen vacancies in hematite nanostructures for solar water oxidation with high efficiency, Journal of Materials Chemistry A 2 (2014) 2491-2497.
[148]X. Qi, G. She, X. Huang, T. Zhang, H. Wang, L. Mu, W. Shi, High-performance n-Si/[small alpha]-Fe2O3 core/shell nanowire array photoanode towards photoelectrochemical water splitting, Nanoscale 6 (2014) 3182-3189.
[149]Y. Qiu, S.-F. Leung, Q. Zhang, B. Hua, Q. Lin, Z. Wei, K.-H. Tsui, Y. Zhang, S. Yang, Z. Fan, Efficient Photoelectrochemical Water Splitting with Ultrathin films of Hematite on Three-Dimensional Nanophotonic Structures, Nano Letters 14 (2014) 2123-2129.
[150]S. Rai, A. Ikram, S. Sahai, S. Dass, R. Shrivastav, V.R. Satsangi, Morphological, optical and photoelectrochemical properties of Fe2O3-GNP composite thin films, RSC Advances 4 (2014) 17671-17679.
[151]S.C. Riha, B.M. Klahr, E.C. Tyo, S. Seifert, S. Vajda, M.J. Pellin, T.W. Hamann, A.B.F. Martinson, Atomic Layer Deposition of a Submonolayer Catalyst for the Enhanced Photoelectrochemical Performance of Water Oxidation with Hematite, ACS Nano 7 (2013) 2396-2405.
[152]G.C. Schatz, Theoretical studies of surface enhanced Raman scattering, Accounts of Chemical Research 17 (1984) 370-376.
[153]R. Schrebler, L.A. Ballesteros, H. Gómez, P. Grez, R. Córdova, E. Muñoz, R. Schrebler, J.R. Ramos-Barrado, E.A. Dalchiele, Electrochemically Grown Self-Organized Hematite Nanotube Arrays for Photoelectrochemical Water Splitting, Journal of The Electrochemical Society 161 (2014) H903-H908.
[154]R.S. Schrebler, L. Ballesteros, A. Burgos, E.C. Muñoz, P. Grez, D. Leinen, F. Martín, J. Ramón Ramos-Barrado, E.A. Dalchiele, Electrodeposited Nanostructured α-Fe2O3 Photoanodes for Solar Water Splitting: Effect of Surface Co-Modification on Photoelectrochemical Performance, Journal of The Electrochemical Society 158 (2011) D500-D505.
[155]H.J. Schugar, G.R. Rossman, J. Thibeault, H.B. Gray, Simultaneous pair electronic excitations in a binuclear iron(III) complex, Chemical Physics Letters 6 (1970) 26-28.
[156]S. Shen, P. Guo, D.A. Wheeler, J. Jiang, S.A. Lindley, C.X. Kronawitter, J.Z. Zhang, L. Guo, S.S. Mao, Physical and photoelectrochemical properties of Zr-doped hematite nanorod arrays, Nanoscale 5 (2013) 9867-9874.
[157]S. Shen, J. Zhou, C.-L. Dong, Y. Hu, E.N. Tseng, P. Guo, L. Guo, S.S. Mao, Surface Engineered Doping of Hematite Nanorod Arrays for Improved Photoelectrochemical Water Splitting, Sci. Rep. 4 (2014).
[158]D.M. SHERMAN, &, T.D. WAITE, ELECTRONIC-SPECTRA OF FE-3+ OXIDES AND OXIDE HYDROXIDES IN THE NEAR IR TO NEAR UV, American Mineralogist 70 (1985) 1262-1269.
[159]Y. Shi, H. Li, L. Wang, W. Shen, H. Chen, Novel α-Fe2O3/CdS Cornlike Nanorods with Enhanced Photocatalytic Performance, ACS Applied Materials & Interfaces 4 (2012) 4800-4806.
[160]K. Sivula, Metal Oxide Photoelectrodes for Solar Fuel Production, Surface Traps, and Catalysis, The Journal of Physical Chemistry Letters 4 (2013) 1624-1633.
[161]K. Sivula, F.L. Formal, M. Grätzel, WO3−Fe2O3 Photoanodes for Water Splitting: A Host Scaffold, Guest Absorber Approach, Chemistry of Materials 21 (2009) 2862-2867.
[162]K. Sivula, F. Le Formal, M. Grätzel, Solar Water Splitting: Progress Using Hematite (α-Fe2O3) Photoelectrodes, ChemSusChem 4 (2011) 432-449.
[163]K. Sivula, R. Zboril, F. Le Formal, R. Robert, A. Weidenkaff, J. Tucek, J. Frydrych, M. Grätzel, Photoelectrochemical Water Splitting with Mesoporous Hematite Prepared by a Solution-Based Colloidal Approach, Journal of the American Chemical Society 132 (2010) 7436-7444.
[164]G.P. Smestad, F.C. Krebs, C.M. Lampert, C.G. Granqvist, K.L. Chopra, X. Mathew, H. Takakura, Reporting solar cell efficiencies in Solar Energy Materials and Solar Cells, Solar Energy Materials and Solar Cells 92 (2008) 371-373.
[165]H.R. Sprunken, R. Schumacher, R.N. Schindler, Evaluation of the flat-band potentials by measurements of anodic/cathodic photocurrent transitions, Faraday Discussions of the Chemical Society 70 (1980) 55-66.
[166]Y. Surendranath, M.W. Kanan, D.G. Nocera, Mechanistic Studies of the Oxygen Evolution Reaction by a Cobalt-Phosphate Catalyst at Neutral pH, Journal of the American Chemical Society 132 (2010) 16501-16509.
[167]A.G. Tamirat, W.-N. Su, A.A. Dubale, H.-M. Chen, B.-J. Hwang, Photoelectrochemical water splitting at low applied potential using a NiOOH coated codoped (Sn, Zr) [small alpha]-Fe2O3 photoanode, Journal of Materials Chemistry A 3 (2015) 5949-5961.
[168]A.G. Tamirat, W.-n. Su, A.A. Dubale, H.-M. Chen, B.J. Hwang, Photoelectrochemical water splitting at low applied potential using NiOOH coated codoped (Sn, Zr) [small alpha]-Fe2O3 photoanode, Journal of Materials Chemistry A (2015).
[169]A.G. Tamirat, W.-N. Su, A.A. Dubale, C.-J. Pan, H.-M. Chen, D.W. Ayele, J.-F. Lee, B.-J. Hwang, Efficient photoelectrochemical water splitting using three dimensional urchin-like hematite nanostructure modified with reduced graphene oxide, Journal of Power Sources 287 (2015) 119-128.
[170]E. Thimsen, F. Le Formal, M. Grätzel, S.C. Warren, Influence of Plasmonic Au Nanoparticles on the Photoactivity of Fe2O3 Electrodes for Water Splitting, Nano Letters 11 (2010) 35-43.
[171]I. Thomann, B.A. Pinaud, Z. Chen, B.M. Clemens, T.F. Jaramillo, M.L. Brongersma, Plasmon Enhanced Solar-to-Fuel Energy Conversion, Nano Letters 11 (2011) 3440-3446.
[172]S.D. Tilley, M. Cornuz, K. Sivula, M. Grätzel, Light-Induced Water Splitting with Hematite: Improved Nanostructure and Iridium Oxide Catalysis, Angewandte Chemie International Edition 49 (2010) 6405-6408.
[173]T.K. Townsend, E.M. Sabio, N.D. Browning, F.E. Osterloh, Photocatalytic water oxidation with suspended alpha-Fe2O3 particles-effects of nanoscaling, Energy & Environmental Science 4 (2011) 4270-4275.
[174]W. Tu, Y. Zhou, Z. Zou, Versatile Graphene-Promoting Photocatalytic Performance of Semiconductors: Basic Principles, Synthesis, Solar Energy Conversion, and Environmental Applications, Advanced Functional Materials 23 (2013) 4996-5008.
[175]Y.-H.C.a.K.-J. Tu, Thickness Dependent on Photocatalytic Activity of Hematite Thin Films, International Journal of Photoenergy 2012 (2012) 1-6.
[176]R. van de Krol, Y. Liang, J. Schoonman, Solar hydrogen production with nanostructured metal oxides, Journal of Materials Chemistry 18 (2008) 2311-2320.
[177]T. Vincent, M. Gross, H. Dotan, A. Rothschild, Thermally oxidized iron oxide nanoarchitectures for hydrogen production by solar-induced water splitting, International Journal of Hydrogen Energy 37 (2012) 8102-8109.
[178]M.G. Walter, E.L. Warren, J.R. McKone, S.W. Boettcher, Q. Mi, E.A. Santori, N.S. Lewis, Solar Water Splitting Cells, Chemical Reviews 110 (2010) 6446-6473.
[179]G. Wang, Y. Ling, X. Lu, T. Zhai, F. Qian, Y. Tong, Y. Li, A mechanistic study into the catalytic effect of Ni(OH)2 on hematite for photoelectrochemical water oxidation, Nanoscale 5 (2013) 4129-4133.
[180]G. Wang, Y. Ling, H. Wang, L. Xihong, Y. Li, Chemically modified nanostructures for photoelectrochemical water splitting, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 19 (2014) 35-51.
[181]G. Wang, Y. Ling, D.A. Wheeler, K.E.N. George, K. Horsley, C. Heske, J.Z. Zhang, Y. Li, Facile Synthesis of Highly Photoactive α-Fe2O3-Based Films for Water Oxidation, Nano Letters 11 (2011) 3503-3509.
[182]K.X. Wang, Z. Yu, V. Liu, M.L. Brongersma, T.F. Jaramillo, S. Fan, Nearly Total Solar Absorption in Ultrathin Nanostructured Iron Oxide for Efficient Photoelectrochemical Water Splitting, ACS Photonics 1 (2014) 235-240.
[183]L. Wang, C.-Y. Lee, R. Kirchgeorg, H. Hildebrand, J. Muller, E. Spiecker, P. Schmuki, A significant cathodic shift in the onset potential of photoelectrochemical water splitting for hematite nanostructures grown from Fe-Si alloys, Materials Horizons 1 (2014) 344-347.
[184]L. Wang, C.-Y. Lee, P. Schmuki, Ti and Sn co-doped anodic α-Fe2O3 films for efficient water splitting, Electrochemistry Communications 30 (2013) 21-25.
[185]P. Wang, D. Wang, J. Lin, X. Li, C. Peng, X. Gao, Q. Huang, J. Wang, H. Xu, C. Fan, Lattice Defect-Enhanced Hydrogen Production in Nanostructured Hematite-Based Photoelectrochemical Device, ACS Applied Materials & Interfaces 4 (2012) 2295-2302.
[186]X. Wang, K.-Q. Peng, Y. Hu, F.-Q. Zhang, B. Hu, L. Li, M. Wang, X.-M. Meng, S.-T. Lee, Silicon/Hematite Core/Shell Nanowire Array Decorated with Gold Nanoparticles for Unbiased Solar Water Oxidation, Nano Letters 14 (2013) 18-23.
[187]S.C. Warren, E. Thimsen, Plasmonic solar water splitting, Energy & Environmental Science 5 (2012) 5133-5146.
[188]S.C. Warren, K. Voïtchovsky, Hen Dotan, Celine M. Leroy, Maurin Cornuz, Francesco Stellacci, Cécile Hébert, A. Rothschild, M. Grätzel, Identifying champion nanostructures for solar water-splitting, Nature Materials 12 (2013) 842–849.
[189]H. Wender, R.V. Goncalves, C.S.B. Dias, M.J.M. Zapata, L.F. Zagonel, E.C. Mendonca, S.R. Teixeira, F. Garcia, Photocatalytic hydrogen production of Co(OH)2 nanoparticle-coated [small alpha]-Fe2O3 nanorings, Nanoscale 5 (2013) 9310-9316.
[190]L. Xi, P.S. Bassi, S.Y. Chiam, W.F. Mak, P.D. Tran, J. Barber, J.S. Chye Loo, L.H. Wong, Surface treatment of hematite photoanodes with zinc acetate for water oxidation, Nanoscale 4 (2012) 4430-4433.
[191]L. Xi, S.Y. Chiam, W.F. Mak, P.D. Tran, J. Barber, S.C.J. Loo, L.H. Wong, A novel strategy for surface treatment on hematite photoanode for efficient water oxidation, Chemical Science 4 (2013) 164-169.
[192]L. Xi, P.D. Tran, S.Y. Chiam, P.S. Bassi, W.F. Mak, H.K. Mulmudi, S.K. Batabyal, J. Barber, J.S.C. Loo, L.H. Wong, Co3O4-Decorated Hematite Nanorods As an Effective Photoanode for Solar Water Oxidation, The Journal of Physical Chemistry C 116 (2012) 13884-13889.
[193]Q. Xiang, J. Yu, M. Jaroniec, Graphene-based semiconductor photocatalysts, Chemical Society Reviews 41 (2012) 782-796.
[194]J. Yang, D. Wang, H. Han, C. Li, Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis, Accounts of Chemical Research 46 (2013) 1900-1909.
[195]X. Yang, R. Liu, C. Du, P. Dai, Z. Zheng, D. Wang, Improving Hematite-based Photoelectrochemical Water Splitting with Ultrathin TiO2 by Atomic Layer Deposition, ACS Applied Materials & Interfaces 6 (2014) 12005-12011.
[196]W. Yaoming, Y. Tao, C. Xinyi, Z. Haitao, O. Shuxin, L. Zhaosheng, Y. Jinhua, Z. Zhigang, Enhancement of photoelectric conversion properties of SrTiO 3 /α-Fe 2 O 3 heterojunction photoanode, Journal of Physics D: Applied Physics 40 (2007) 3925.
[197]T.-F. Yeh, F.-F. Chan, C.-T. Hsieh, H. Teng, Graphite Oxide with Different Oxygenated Levels for Hydrogen and Oxygen Production from Water under Illumination: The Band Positions of Graphite Oxide, The Journal of Physical Chemistry C 115 (2011) 22587-22597.
[198]T.-F. Yeh, S.-J. Chen, C.-S. Yeh, H. Teng, Tuning the Electronic Structure of Graphite Oxide through Ammonia Treatment for Photocatalytic Generation of H2 and O2 from Water Splitting, The Journal of Physical Chemistry C 117 (2013) 6516-6524.
[199]B.S. Yeo, A.T. Bell, In Situ Raman Study of Nickel Oxide and Gold-Supported Nickel Oxide Catalysts for the Electrochemical Evolution of Oxygen, The Journal of Physical Chemistry C 116 (2012) 8394-8400.
[200]J. Young Kim, J.-W. Jang, D. Hyun Youn, J. Yul Kim, E. Sun Kim, J. Sung Lee, Graphene-carbon nanotube composite as an effective conducting scaffold to enhance the photoelectrochemical water oxidation activity of a hematite film, RSC Advances 2 (2012) 9415-9422.
[201]K.M.H. Young, T.W. Hamann, Enhanced photocatalytic water oxidation efficiency with Ni(OH)2 catalysts deposited on [small alpha]-Fe2O3via ALD, Chemical Communications 50 (2014) 8727-8730.
[202]K.M.H. Young, B.M. Klahr, O. Zandi, T.W. Hamann, Photocatalytic water oxidation with hematite electrodes, Catalysis Science & Technology 3 (2013) 1660-1671.
[203]G. Yuzheng, J.C. Stewart, R. John, Electronic and magnetic properties of Ti 2 O 3 , Cr 2 O 3 , and Fe 2 O 3 calculated by the screened exchange hybrid density functional, Journal of Physics: Condensed Matter 24 (2012) 325504.
[204]O. Zandi, T.W. Hamann, Enhanced Water Splitting Efficiency Through Selective Surface State Removal, The Journal of Physical Chemistry Letters 5 (2014) 1522-1526.
[205]O. Zandi, B.M. Klahr, T.W. Hamann, Highly photoactive Ti-doped [small alpha]-Fe2O3 thin film electrodes: resurrection of the dead layer, Energy & Environmental Science 6 (2013) 634-642.
[206]H. Zhang, X. Lv, Y. Li, Y. Wang, J. Li, P25-Graphene Composite as a High Performance Photocatalyst, ACS Nano 4 (2009) 380-386.
[207]L. Zhang, Y. Zhong, Z. He, J. Wang, J. Xu, J. Cai, N. Zhang, H. Zhou, H. Fan, H. Shao, J. Zhang, C.-n. Cao, Surfactant-assisted photochemical deposition of three-dimensional nanoporous nickel oxyhydroxide films and their energy storage and conversion properties, Journal of Materials Chemistry A 1 (2013) 4277-4285.
[208]Z. Zhang, J.T. Yates, Band Bending in Semiconductors: Chemical and Physical Consequences at Surfaces and Interfaces, Chemical Reviews 112 (2012) 5520-5551.
[209]J. Zhao, F.E. Huggrns, Z. Feng, G.P. Huffman, Ferrihydrite: Surface Structure and its Effects on Phase Transformation, Clays and Clay Minerals 42 (1994) 737-746.
[210]P. Zhao, C.X. Kronawitter, X. Yang, J. Fu, B.E. Koel, WO3-[small alpha]-Fe2O3 composite photoelectrodes with low onset potential for solar water oxidation, Physical Chemistry Chemical Physics 16 (2014) 1327-1332.
[211]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 [small alpha]-Fe2O3 dendritic wire array, CrystEngComm 14 (2012) 6957-6961.
[212]D.K. Zhong, S. Choi, D.R. Gamelin, Near-Complete Suppression of Surface Recombination in Solar Photoelectrolysis by “Co-Pi” Catalyst-Modified W:BiVO4, Journal of the American Chemical Society 133 (2011) 18370-18377.
[213]D.K. Zhong, M. Cornuz, K. Sivula, M. Gratzel, D.R. Gamelin, Photo-assisted electrodeposition of cobalt-phosphate (Co-Pi) catalyst on hematite photoanodes for solar water oxidation, Energy & Environmental Science 4 (2011) 1759-1764.
[214]D.K. Zhong, D.R. Gamelin, Photoelectrochemical Water Oxidation by Cobalt Catalyst (“Co−Pi”)/α-Fe2O3 Composite Photoanodes: Oxygen Evolution and Resolution of a Kinetic Bottleneck, Journal of the American Chemical Society 132 (2010) 4202-4207.