Initial studies on the hydrogen gas sensing properties of highly-ordered high aspect ratio TiO2 nanotube-arrays 20 μm to 222 μm in length

Described is the fabrication and hydrogen gas sensing properties of self-aligned highly-ordered TiO2 nanotube arrays having lengths up to 222 mu m with a length-to-outer diameter aspect ratio of approximate to 1,500. The nanotube arrays are made by potentiostatic anodization of Ti foil in fluoride ion 0 containing baths in combination with a variety of non-aqueous organic polar electrolytes including formamide, N-methylformamide, dimethyl sulfoxide, and ethylene glycol. The inner pore diameters of the resulting nanotube arrays range from 20 nm to 150 nm depending upon the anodization voltage. The as-prepared nanotubes are amorphous and show no gas-sensing capabilities. The nanotube arrays crystallize upon annealing at elevated temperatures, approximate to 550 degrees C, and subsequently demonstrate excellent hydrogen gas sensing capabilities but suffer from significant response and recovery times.