Design of anodically oxidized metal oxide films as a gas sensor material

H₂ sensing properties of an anodically oxidized Nb₂O₅ film coupled with a noble metal electrode (M/Nb₂O₅, M:Au, Pt and Pd) have been investigated under various operating conditions. Among the sensors tested, the Nb₂O₅ film with a Pd electrode, which was prepared by anodic oxidation in an aqueous solution of 0.5 M H₂SO₄, showed the highest H₂ response, and the logarithmic sensor current under a forward bias was proportional to the logarithmic H₂ concentration. The current-voltage characteristics of the Pd/Nb₂O₅ sensor at 100°C apparently showed a typical rectifying function of a metal-semiconductor junction, which was formed between the Pd electrode and the Nb₂O₅ thin film, especially in H₂ balanced with dry air. The H₂ response property was improved when it was operated under a forward bias above 150°C. Furthermore, it was confirmed that even at 28°C the Pd/Nb₂O₅ could respond to H₂ in dry air.