Effect of Ni, Pd, and Pt Nanoparticle Dispersion on Thick Films of TiO2 Nanotubes for Hydrogen Sensing: TEM and XPS Studies

Crystal structure, morphological features, and hydrogen-sensing properties of thick film sensors of TiO 2 nanotubes (NTs) impregnated with nanoparticles of elements of Group 10, viz., nickel, palladium, and platinum, having average grain size of about 25, 20, and 20 nm, respectively, are presented. The sensitivity is observed to be higher for Pd/TiO 2 NTs than for Pt/TiO 2 NTs. Ni/TiO 2 NTs exhibited very poor sensitivity. X-ray photoelectron spectroscopy (XPS) studies confirm reduction of the oxide layer of palladium nanoparticles, which, in turn, is responsible for the generation of Ti 3+ ion in TiO 2 NTs through hydrogen spillover. For Pt/TiO 2 NTs, only reduction of the oxide layer over Pt nanoparticles takes place without any spillover effect. For Ni/TiO 2 NTs, neither NiO nor TiO 2 undergoes any reduction. Changes in the Fermi level difference of PdO and TiO 2 along with Ti 3+ generation synergistically operate for Pd/TiO 2 NTs, whereas the difference in Fermi levels of PtO and TiO 2 alone operates for Pt/TiO 2 NTs during sensing.