Hydrogen storage characteristics of Ti– and V–based thin films

• Hydrogen storage up to 50 at.% in Ti layers, up to 30 at.% in the layers consisted of Ti, V and Ni metal.
• Hydrogen induces a complete transition of V2O5 to VO2.
• Hydrogen removes the preferential Ti orientation.

Series of thin films of single-, bi- and tri-layered structure consisting of Ti, V, TiO2 and V2O5 layer and/or mixed Ti–V–Ni layer with different layer sequences and thicknesses were prepared by the sputtering technique on Si and SiO2 substrates. The layer chemical composition and thickness were determined by a combined analysis of X-ray diffraction, X-ray reflectometry, Rutherford backscattering and optical reflectivity spectra. The films were hydrogenated at 1 bar at 300 °C and/or at high pressures up to 100 bar at room temperature. The hydrogen concentration and hydrogen profile was determined by means of a secondary ion mass spectroscopy and N-15 Nuclear Reaction Analysis. The highest hydrogen storage with a concentration up to 50 at.% was found in the pure Ti layers, while it amounts to about 30 at.% in the metallic Ti–V–Ni layers. A large hydrogen storage (up to 20 at.%) was also found in the V2O5 layers, while no hydrogen accumulation was found in the TiO2 layers. Hydrogen could remove the preferential orientation of the Ti films and induce a complete transition of V2O5 to VO2.