Unprecedented ultra-high hydrogen gas sensitivity in undoped titania nanotubes

A highly ordered array of micron-length undoped titania nanotubes exhibits an unprecedented variation in electrical resistance of about 8.7 orders of magnitude (50 000 000 000%), at room temperature, when exposed to alternating atmospheres of nitrogen containing 1000 ppm hydrogen and air. This represents the largest known change in electrical properties of any material, to any gas, at any temperature. The nanotube arrays were fabricated using anodic oxidation of titanium foil in a pH 4.0 electrolyte containing potassium fluoride, sodium hydrogen sulfate monohydrate and sodium citrate tribasic dihydrate. The dramatic change in resistance is believed to be due to the highly active surface states on the nanoscale walls of the tubes, high surface area of the nanotube architecture, and the well-ordered geometry allowing for hydrogen-sensitive tube-to-tube electrical connections.