Visible light driven photoelectrochemical water oxidation on nitrogen-modified TiO2 nanowires.

We report hydrothermal synthesis of single crystalline TiO(2) nanowire arrays with unprecedented small feature sizes of ~5 nm and lengths up to 4.4 μm on fluorine-doped tin oxide substrates. A substantial amount of nitrogen (up to 1.08 atomic %) can be incorporated into the TiO(2) lattice via nitridation in NH(3) flow at a relatively low temperature (500 °C) because of the small cross-section of the nanowires. The low-energy threshold of the incident photon to current efficiency (IPCE) spectra of N-modified TiO(2) samples is at ~520 nm, corresponding to 2.4 eV. We also report a simple cobalt treatment for improving the photoelectrochemical (PEC) performance of our N-modified TiO(2) nanowire arrays. With the cobalt treatment, the IPCE of N-modified TiO(2) samples in the ultraviolet region is restored to equal or higher values than those of the unmodified TiO(2) samples, and it remains as high as ~18% at 450 nm. We propose that the cobalt treatment enhances PEC performance via two mechanisms: passivating surface states on the N-modified TiO(2) surface and acting as a water oxidation cocatalyst.

[1]  A. Bard,et al.  Screening of Electrocatalysts for Photoelectrochemical Water Oxidation on W-Doped BiVO4 Photocatalysts by Scanning Electrochemical Microscopy , 2011 .

[2]  Xiaobo Chen,et al.  The electronic origin of the visible-light absorption properties of C-, N- and S-doped TiO2 nanomaterials. , 2008, Journal of the American Chemical Society.

[3]  Ryuhei Nakamura,et al.  Mechanism for Visible Light Responses in Anodic Photocurrents at N-Doped TiO2 Film Electrodes , 2004 .

[4]  H. Tributsch,et al.  Exploring the electronic structure of nitrogen-modified TiO2 photocatalysts through photocurrent and surface photovoltage studies , 2007 .

[5]  Jing Sun,et al.  Template-free synthesis of hierarchical TiO2 structures and their application in dye-sensitized solar cells. , 2011, ACS applied materials & interfaces.

[6]  A. Manivannan,et al.  Origin of photocatalytic activity of nitrogen-doped TiO2 nanobelts. , 2009, Journal of the American Chemical Society.

[7]  Yasunori Taga,et al.  Electronic and optical properties of anatase TiO2 , 2000 .

[8]  R. Egdell,et al.  High resolution X-ray photoemission study of nitrogen doped TiO2 rutile single crystals , 2008 .

[9]  R. Asahi,et al.  Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides , 2001, Science.

[10]  Xiaobo Chen,et al.  Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications. , 2007, Chemical reviews.

[11]  Suhuai Wei,et al.  Design of narrow-gap TiO2: a passivated codoping approach for enhanced photoelectrochemical activity. , 2009, Physical review letters.

[12]  A. Fujishima,et al.  TiO2 photocatalysis and related surface phenomena , 2008 .

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

[14]  K. Hashimoto,et al.  Visible-light induced hydrophilicity on nitrogen-substituted titanium dioxide films. , 2003, Chemical communications.

[15]  J. Yates,et al.  Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results , 1995 .

[16]  T. Ohsawa,et al.  Epitaxial Growth and Orientational Dependence of Surface Photochemistry in Crystalline TiO2 Rutile Films Doped with Nitrogen , 2010 .

[17]  J. Bell,et al.  One-step synthesis of titanium oxide with trilayer structure for dye-sensitized solar cells , 2011 .

[18]  C. Grimes,et al.  Vertically aligned single crystal TiO2 nanowire arrays grown directly on transparent conducting oxide coated glass: synthesis details and applications. , 2008, Nano letters.

[19]  G. M. Stocks,et al.  Band gap narrowing of titanium oxide semiconductors by noncompensated anion-cation codoping for enhanced visible-light photoactivity. , 2009, Physical review letters.

[20]  Nick Serpone,et al.  Is the band gap of pristine TiO(2) narrowed by anion- and cation-doping of titanium dioxide in second-generation photocatalysts? , 2006, The journal of physical chemistry. B.

[21]  Claes-Göran Granqvist,et al.  Photoelectrochemical study of sputtered nitrogen-doped titanium dioxide thin films in aqueous electrolyte , 2004 .

[22]  J. Gole,et al.  Enhanced Nitrogen Doping in TiO2 Nanoparticles , 2003 .

[23]  Suhuai Wei,et al.  Band structure engineering of semiconductors for enhanced photoelectrochemical water splitting: The case of TiO 2 , 2010 .

[24]  K. Hashimoto,et al.  Zeta potential and photocatalytic activity of nitrogen doped TiO2 thin films , 2004 .

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

[26]  Claes-Göran Granqvist,et al.  Photoelectrochemical Study of Nitrogen-Doped Titanium Dioxide for Water Oxidation , 2004 .

[27]  Alexander J. Cowan,et al.  Mechanism of O2 Production from Water Splitting: Nature of Charge Carriers in Nitrogen Doped Nanocrystalline TiO2 Films and Factors Limiting O2 Production , 2011 .

[28]  Michael Grätzel,et al.  New Benchmark for Water Photooxidation by Nanostructured α-Fe2O3 Films , 2006 .

[29]  Yuka Watanabe,et al.  Nitrogen-Concentration Dependence on Photocatalytic Activity of TiO2-xNx Powders , 2003 .

[30]  Kazunari Domen,et al.  Facile fabrication of an efficient oxynitride TaON photoanode for overall water splitting into H2 and O2 under visible light irradiation. , 2010, Journal of the American Chemical Society.

[31]  Oliver Diwald,et al.  Photochemical Activity of Nitrogen-Doped Rutile TiO2(110) in Visible Light , 2004 .

[32]  A. Emeline,et al.  Photoinduced Formation of Defects and Nitrogen Stabilization of Color Centers in N-Doped Titanium Dioxide , 2007 .

[33]  Daniel G. Nocera,et al.  In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+ , 2008, Science.

[34]  Ulrike Diebold,et al.  Influence of nitrogen doping on the defect formation and surface properties of TiO2 rutile and anatase. , 2006, Physical review letters.

[35]  P. Salvador,et al.  Hole diffusion length in n‐TiO2 single crystals and sintered electrodes: Photoelectrochemical determination and comparative analysis , 1984 .