High H2 sensing behavior of TiO2 films formed by thermal oxidation

A highly sensitive H2 gas sensor was prepared by the thermal oxidation of a Ti plate at 600–1000 °C. The H2 sensitivity (the ratio of the resistances between N2 and 1.0% H2 balanced with N2) of the oxidized TiO2 increased exponentially with increasing oxidation temperature up to 900 °C but decreased drastically at 1000 °C. The maximum sensitivity to 1.0% H2 was 1.2 × 106, which is the highest value reported in the literature. The mechanism for the enhanced H2 sensing was examined by investigating the phase, thickness and morphology of the oxidized TiO2 layer and the sensor response time. The thermally oxidized specimens exhibited an approximately linear dependence of the sensitivity on the H2 concentrations from 50 to 10,000 ppm, and excellent sensitivity (∼103) was still obtained in the sensor operated at temperatures as low as 150 °C.