Enhanced photoelectrochemical-response in highly ordered TiO2 nanotube-arrays anodized in boric acid containing electrolyte

Abstract We examine the photoelectrochemical properties of highly ordered titanium dioxide nanotube-array photoanodes, fabricated by anodization of titanium in a nitric acid/hydrofluoric acid electrolyte, with and without the addition of boric acid. Under UV–Vis illumination the photocurrent densities achieved with TiO 2 nanotube-arrays fabricated in the H 3 BO 3 –HNO 3 –HF electrolyte are a factor of seven greater than the TiO 2 nanotube-array samples obtained in the commonly used HNO 3 –HF electrolyte, indicating the ability to control the photoelectrochemical response of the highly ordered nanotube arrays by tailoring the electrolyte composition. For 560 nm long boric-acid fabricated nanotube arrays, a photoconversion efficiency of 7.9% is achieved upon a 320–400 nm illumination at an intensity of 98 mW/cm 2 , with hydrogen generated by water photoelectrolysis at the power-time normalized rate of 1708-μmol/h W (42 ml/h W). The resulting nanotube-arrays demonstrate excellent photocorrosion stability, with no detectable degradation in photoconversion properties over 6 months of testing. While the titania bandgap is not suitable for high visible spectrum efficiencies, the high photoconversion efficiency achieved under UV illumination indicates the suitability of the highly ordered nanotube-array architecture for hydrogen generation by water photoelectrolysis.

[1]  K. G. Ong,et al.  Highly Ordered Nanoporous Alumina Films: Effect of Pore Size and Uniformity on Sensing Performance , 2002 .

[2]  Patrik Schmuki,et al.  Thick self-organized porous zirconium oxide formed in H2SO4/NH4F electrolytes , 2004 .

[3]  M. Grätzel.  Mesoporous oxide junctions and nanostructured solar cells , 1999 .

[4]  Kenji Fukuda,et al.  Ordered Metal Nanohole Arrays Made by a Two-Step Replication of Honeycomb Structures of Anodic Alumina , 1995, Science.

[5]  Toshiaki Tamamura,et al.  Highly ordered nanochannel-array architecture in anodic alumina , 1997 .

[6]  Craig A. Grimes,et al.  A Self-Cleaning, Room-Temperature Titania-Nanotube Hydrogen Gas Sensor , 2003 .

[7]  R. Smoluchowski,et al.  Elements of X‐Ray Diffraction , 1957 .

[8]  U. Gösele,et al.  Anodization of nanoimprinted titanium: a comparison with formation of porous alumina , 2004 .

[9]  Patrik Schmuki,et al.  Self-Organized Porous Titanium Oxide Prepared in H 2 SO 4 / HF Electrolytes , 2003 .

[10]  D. Vanmaekelbergh,et al.  Greatly Enhanced Sub‐Bandgap Photocurrent in Porous GaP Photoanodes , 1996 .

[11]  C. Wamser.  Equilibria in the System Boron Trifluoride—Water at 25° , 1951 .

[12]  Craig A. Grimes,et al.  Crystallization and high-temperature structural stability of titanium oxide nanotube arrays , 2003 .

[13]  Harland G. Tompkins,et al.  Titanium nitride oxidation chemistry: An x‐ray photoelectron spectroscopy study , 1992 .

[14]  G. Thompson,et al.  Porous anodic alumina: fabrication, characterization and applications , 1997 .

[15]  B. Erné,et al.  Morphology and Strongly Enhanced Photoresponse of GaP Electrodes Made Porous by Anodic Etching , 1996 .

[16]  H. Föll,et al.  Formation and application of porous silicon , 2002 .

[17]  C. Grimes,et al.  A titania nanotube-array room-temperature sensor for selective detection of hydrogen at low concentrations. , 2004, Journal of nanoscience and nanotechnology.

[18]  Frank Müller,et al.  Self-Organized Formation of Hexagonal Pore Structures in Anodic Alumina , 1998 .

[19]  J. Lagemaat,et al.  Enhancement of the light‐to‐current conversion efficiency in an n‐SiC/solution diode by porous etching , 1996 .

[20]  S. R. Biaggio,et al.  XPS characterization of anodic titanium oxide films grown in phosphate buffer solutions , 2004 .

[21]  D. Dyer,et al.  Hydrolysis of titanium tetrafluoride , 1967 .

[22]  Craig A. Grimes,et al.  Titanium oxide nanotube arrays prepared by anodic oxidation , 2001 .

[23]  A. Zaban,et al.  Mesoporous titanium dioxide: sonochemical synthesis and application in dye-sensitized solar cells , 2001 .

[24]  B. Erné,et al.  Porous etching: A means to enhance the photoresponse of indirect semiconductors , 1995 .

[25]  Heon-Cheol Shin,et al.  Porous Tin Oxides Prepared Using an Anodic Oxidation Process , 2004 .

[26]  Craig A Grimes,et al.  Enhanced photocleavage of water using titania nanotube arrays. , 2005, Nano letters.

[27]  W. Ingler,et al.  Efficient Photochemical Water Splitting by a Chemically Modified n-TiO2 , 2002, Science.

[28]  P. Schmuki,et al.  Electrochemical formation of porous superlattices on n-type (1 0 0) InP , 2003 .

[29]  Craig A. Grimes,et al.  The effect of electrolyte composition on the fabrication of self-organized titanium oxide nanotube arrays by anodic oxidation , 2005 .