Homojunction TiO2 thin film-based room-temperature working H2 sensors with non-noble metal electrodes

Metal oxide semiconductor heterojunctions and homojunctions are considered to have better performance than single phase material for room temperature hydrogen gas sensing. In this work, TiO2 facet homojunction (TiO2- FH) thin films were prepared by a two-step hydrothermal method. The TiO2-FH thin films were decorated with Pt nanoparticles using a green photodeposition method and then evaluated for H2 sensing. Non-noble metal Al was used as finger electrodes instead of noble metal Pt. Compared with the TiO2-FH sensor, the H2 detection limits of the platinum loaded TiO2-FH@Pt sensors are remarkably decreased from 8000 ppm to 1 ppm at room temper-ature. The optimized sensor achieves an excellent sensing performance of S = 1.21 and fast response / recovery times of about 42 s / 30 s when exposed to 1 ppm H2 concentration. The synergy between the Schottky barrier at the Pt/TiO2 interface and the barrier between the (110) and (001) facets of TiO2 is the key to the improvement of the sensing performance. Replacement of noble metal Pt with Al and C electrodes greatly help to clarify the mechanism of the junctions in the thin film sensors, especially the function of the Pt/TiO2 junction and the (110)/(001) TiO2 junction. The simple and green fabrication method and cheap Al interdigitated electrodes are advantageous for practical applications.