Reactive ballistic deposition of alpha-Fe2O3 thin films for photoelectrochemical water oxidation.

We report the preparation of alpha-Fe2O3 electrodes using a technique known as reactive ballistic deposition in which iron metal is evaporatively deposited in an oxygen ambient for photoelectrochemical (PEC) water oxidation. By manipulating synthesis parameters such as deposition angle, film thickness, and annealing temperature, we find that it is possible to optimize the structural and morphological properties of such films in order to improve their PEC efficiency. Incident photon to current conversion efficiencies (IPCE) are used to calculate an AM1.5 photocurrent of 0.55 mA/cm(2) for optimized films with an IPCE reaching 10% at 420 nm in 1 M KOH at +0.5 V versus Ag/AgCl. We also note that the commonly observed low photoactivity of extremely thin hematite films on fluorine-doped tin oxide substrates may be improved by modification of annealing conditions in some cases.

[1]  Michael Grätzel,et al.  Visible light-induced water oxidation on mesoscopic α-Fe2O3 films made by ultrasonic spray pyrolysis , 2005 .

[2]  Wilson A. Smith,et al.  Photoelectrochemical water splitting using dense and aligned TiO2 nanorod arrays. , 2009, Small.

[3]  B. D. Kay,et al.  Structural characterization of nanoporous Pd films grown via ballistic deposition , 2005 .

[4]  M. Graetzel,et al.  New Benchmark for Water Photooxidation by Nanostructured α‐Fe2O3 Films. , 2007 .

[5]  J. Bockris,et al.  Thin film photoelectrochemistry: Iron oxide , 1984 .

[6]  Piers R. F. Barnes,et al.  Enhancement of Photoelectrochemical Hydrogen Production from Hematite Thin Films by the Introduction of Ti and Si , 2007 .

[7]  C. Grimes,et al.  Temperature-Dependent Growth of Self-Assembled Hematite (α-Fe2O3) Nanotube Arrays: Rapid Electrochemical Synthesis and Photoelectrochemical Properties , 2009 .

[8]  M. J. Brett,et al.  Chiral sculptured thin films , 1996, Nature.

[9]  Alice Dohnalkova,et al.  Structural and Chemical Characterization of Aligned Crystalline Nanoporous MgO Films Grown via Reactive Ballistic Deposition , 2002 .

[10]  Arnold J. Forman,et al.  Pt‐Doped α‐Fe2O3 Thin Films Active for Photoelectrochemical Water Splitting. , 2008 .

[11]  B. D. Kay,et al.  Reactive Ballistic Deposition of Porous TiO2 Films: Growth and Characterization , 2007 .

[12]  K. Stevenson,et al.  Low Temperature Synthesis and Characterization of Nanocrystalline Titanium Carbide with Tunable Porous Architectures , 2010 .

[13]  E. F. Schubert,et al.  Light‐Extraction Enhancement of GaInN Light‐Emitting Diodes by Graded‐Refractive‐Index Indium Tin Oxide Anti‐Reflection Contact , 2008 .

[14]  Nathan T. Hahn,et al.  Growth and Characterization of High Surface Area Titanium Carbide , 2009 .

[15]  A. Bard,et al.  SEMICONDUCTOR ELECTRODES. V. THE APPLICATION OF CHEMICALLY VAPOR DEPOSITED IRON OXIDE FILMS TO PHOTOSENSITIZED ELECTROLYSIS , 1976 .

[16]  A. Bard,et al.  Novel carbon-doped TiO2 nanotube arrays with high aspect ratios for efficient solar water splitting. , 2006, Nano letters.

[17]  J. Kennedy,et al.  FLATBAND POTENTIALS AND DONOR DENSITIES OF POLYCRYSTALLINE α-IRON(III) OXIDE DETERMINED FROM MOTT-SCHOTTKY PLOTS , 1978 .

[18]  Ryan L. Spray,et al.  Photoactivity of Transparent Nanocrystalline Fe2O3 Electrodes Prepared via Anodic Electrodeposition , 2009 .

[19]  Shahed U. M. Khan,et al.  PHOTOELECTROCHEMICAL SPLITTING OF WATER AT NANOCRYSTALLINE N-FE2O3 THIN-FILM ELECTRODES , 1999 .

[20]  S. Ardizzone,et al.  Surface characterization of Co3O4 electrodes prepared by the sol-gel method , 1997 .

[21]  I. E. Grey,et al.  Efficiency of solar water splitting using semiconductor electrodes , 2006 .

[22]  Michael Grätzel,et al.  Anisotropic photocatalytic properties of hematite , 2009, Aquatic Sciences.

[23]  Allen J. Bard,et al.  Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen , 1995 .

[24]  Joop Schoonman,et al.  Solar hydrogen production with nanostructured metal oxides , 2008 .

[25]  E. Fred Schubert,et al.  Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection , 2007 .

[26]  Craig A. Grimes,et al.  Recent Advances in the Use of TiO2 Nanotube and Nanowire Arrays for Oxidative Photoelectrochemistry , 2009 .

[27]  Arthur J. Nozik,et al.  Physical Chemistry of Semiconductor−Liquid Interfaces , 1996 .

[28]  Nathan S. Lewis,et al.  Basic Research Needs for Solar Energy Utilization: report of the Basic Energy Sciences Workshop on Solar Energy Utilization, April 18-21, 2005 , 2005 .

[29]  Arnold J. Forman,et al.  Electrodeposition of α-Fe2O3 Doped with Mo or Cr as Photoanodes for Photocatalytic Water Splitting , 2008 .

[30]  Yiping Zhao,et al.  Photoelectrochemical Study of Nanostructured ZnO Thin Films for Hydrogen Generation from Water Splitting , 2009 .

[31]  A. Fujishima,et al.  Electrochemical Photolysis of Water at a Semiconductor Electrode , 1972, Nature.

[32]  Michael J. Brett,et al.  Glancing angle deposition: Fabrication, properties, and applications of micro- and nanostructured thin films , 2007 .

[33]  M. Misra,et al.  Water Photooxidation by Smooth and Ultrathin α-Fe2O3 Nanotube Arrays , 2009 .

[34]  Fu-Ren F. Fan,et al.  Rapid Screening of Effective Dopants for Fe2O3 Photocatalysts with Scanning Electrochemical Microscopy and Investigation of Their Photoelectrochemical Properties , 2009 .

[35]  E. Longo,et al.  The influence of the film thickness of nanostructured alpha-Fe2O3 on water photooxidation. , 2009, Physical chemistry chemical physics : PCCP.

[36]  R. Černý,et al.  Photoelectrochemical oxidation of water at transparent ferric oxide film electrodes. , 2005, The journal of physical chemistry. B.

[37]  Michael Grätzel,et al.  Influence of Feature Size, Film Thickness, and Silicon Doping on the Performance of Nanostructured Hematite Photoanodes for Solar Water Splitting , 2009 .