Hydrogen generation under sunlight by self ordered TiO2 nanotube arrays

Highly ordered TiO2 nanotube arrays generate a considerable interest for hydrogen generation by an electrochemical photocell, since ordered architecture of nanotube arrays provides a unidirectional electric channel for electron's transport. Here, we report the hydrogen generation by highly ordered TiO2 nanotube arrays under actual sunlight in KOH electrolyte. The two-electrode electrochemical cell included an adjustable anode compartment capable of tracing the trajectory of the sun and a set of alkaline batteries connected with a rheostat for application of external bias. The results showed that the photocurrent responses of nanotube arrays match well with the intensity of solar irradiance on a clear summer day. Addition of ethylene glycol into KOH electrolyte as a hole scavenger enhanced the rate of hydrogen generation. A maximum photocurrent density of 31 mA/cm(2) was observed at 13:30 h, by focusing the sunlight with an intensity of 113 mW/cm 2 on the surface of the TiO2 nanotube arrays in 1 M KOH electrolyte with 10 vol% ethylene glycol under an applied bias of 0.5 V. The observed hydrogen generation rate was 4.4 mL/h cm(2) under the focalized solar irradiance with an intensity between 104 mW/cm(2) and 115 mW/cm(2) from 10:00 to 14:20 h. (C) 2009 Intemational Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.