H2 sensing properties and mechanism of anodically oxidized TiO2 film contacted with Pd electrode

TiO2 thin films have been prepared by anodic oxidation of Ti plates at different temperatures, and H2 sensing properties of the obtained TiO2 thin film sensors equipped with a Pt and Ti electrode have been investigated both in air and N2 under forward and reverse bias conditions. The TiO2 thin film prepared by the anodic oxidation at 20 °C had a large number of sub-micron pores, and exhibited the highest sensitivity and reversible response to H2 both in air and N2 under forward and reverse bias conditions. The current–voltage (I–V) characteristic of the sensor was roughly Ohmic in 0.8% H2 balanced with N2, while it was non-Ohmic in other environments studied. In addition, the change in the Schottky barrier height at the interface between Pd and TiO2 induced by H2 was larger in N2 than in air, and also under reverse bias than forward bias conditions. The reversible and concentration-dependent H2 sensitivity of the sensor in N2 was suggested to arise mainly from the change in the Schottky barrier height induced by dissolution of H atoms in the Pd bulk.