Hydrogen-sensing properties of anodically oxidized TiO2 film sensors: Effects of preparation and pretreatment conditions

Abstract Porous oxide thin films were prepared by anodic oxidation of a Ti plate in H 2 SO 4 and HF solutions. The film (s-TiO 2 ) prepared in the H 2 SO 4 solution was a mixture of anatase and rutile and contained micron-size pores. In contrast, no crystal phase appeared in the film (f-TiO 2 ) prepared in the HF solution, while the film showed submicron-size pores. A Pd electrode was deposited by evaporation on the surface of the film to make a sensor configuration of Pd (top electrode)/oxide film/Ti (bottom electrode). Both the thin film sensors exhibited a fast response to H 2 and fast recovery at 250 °C in air as well as in N 2 atmosphere. The magnitude of the response of s-TiO 2 was superior to that of f-TiO 2 , especially in N 2 atmosphere. The H 2 response of s-TiO 2 at 250 °C in air was found to vary significantly with the pretreatment conditions: additional pretreatment at 600 °C for 1 h in N 2 resulted in a deteriorated H 2 response especially in air, in comparison with that just after the firing at 600 °C for 1 h in air for ensuring the electrical contact. Thus, the surface oxidation state and morphology of the Pd electrode was suggested to affect the H 2 response of the sensors. It was revealed that the s-TiO 2 sensor without additional treatment in N 2 showed superior H 2 -sensing performance to the N 2 -treated s-TiO 2 sensor when operated in N 2 atmosphere. In addition, the response to N 2 -diluted H 2 was larger than that to air-diluted H 2 , and the interference from water vapor was negligible in N 2 atmosphere.