Photoelectrochemical properties of TiO2 nanotube arrays: effect of electrolyte pH and annealing temperature

The effect of electrolyte pH and annealing temperature on the formation of TiO2 nanotube arrays in connection with the photoelectrochemical response was investigated in this article. Well-aligned TiO2 nanotube arrays were fabricated by anodisation of Ti foil in an electrolyte consisting of 1M of glycerol (85wt% of glycerol and 15wt% of water) with 0.5wt% of NH4F at 30V for 30min. The pH of the electrolyte was varied from pH 1 to 7. With the increase of electrolyte pH to neutral condition, the length of the nanotube arrays was increased from approximate to 320 to 1100nm. As-anodised TiO2 nanotube arrays were amorphous in nature. However, anatase phase was observed after annealing at 400 degrees C and polycrystalline anatase and rutile phase could be observed by heating up to 500 degrees C in air atmosphere. Based on the results obtained, the length and crystalline phases of TiO2 nanotube arrays affect the performance of photoelectrochemical response and photoconversion efficiency significantly.