Mechanism of hydrogen modification of titanium-dioxide

Recent explanations of the enhancement of the electrical properties of hydrogen-modified anatase-TiO2 propose mid-band gap states just below the conduction band and relate these to the creation of a disordered surface layer on an unmodified crystalline core. In this paper, the focus is on hydrogen modification of rutile-TiO2 , which also acquires enhanced electrical properties. Oxygen-deficient TiO2-x, was produced by exposing rutile to hydrogen at temperatures up to 730 degrees C. The desorption of hydrogen was studied by mass spectrometry measurements at temperatures up to 730 degrees C. All the evidence gathered in this new study is consistent with the absorption of hydrogen into the interior of the rutile particle. Re-examination of published x-ray diffraction results does not reveal evidence for a disordered surface layer on hydrogen-modified rutile. It therefore appears that the explanation of enhanced electrical properties owing to surface-only processes is incomplete, especially for rutile, but probably for anatase as well. (C) 2019 Elsevier B.V. All rights reserved.