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 TiO₂ 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/TiO₂ NTs than for Pt/TiO₂ NTs. Ni/TiO₂ 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 Ti³⁺ ion in TiO₂ NTs through hydrogen spillover. For Pt/TiO₂ NTs, only reduction of the oxide layer over Pt nanoparticles takes place without any spillover effect. For Ni/TiO₂ NTs, neither NiO nor TiO₂ undergoes any reduction. Changes in the Fermi level difference of PdO and TiO₂ along with Ti³⁺ generation synergistically operate for Pd/TiO₂ NTs, whereas the difference in Fermi levels of PtO and TiO₂ alone operates for Pt/TiO₂ NTs during sensing.