An Ultrasensitive Room-Temperature H 2 Sensor Based on a TiO 2 Rutile-Anatase Homojunction.

Metal oxide semiconductor hetero- and homojunctions are commonly constructed to improve the performance of hydrogen sensors at room temperature. In this study, a simple two-step hydrothermal method was employed to prepare TiO 2 films with homojunctions of rutile and anatase phases (denoted as TiO 2 -R/A). Then, the microstructure of anatase-phase TiO 2 was altered by controlling the amount of hydrochloric acid to realize a more favorable porous structure for charge transport and a larger surface area for contact with H 2 . The sensor used a Pt interdigital electrode. At an optimal HCl dosage (25 mL), anatase-phase TiO 2 uniformly covered rutile-phase TiO 2 nanorods, resulting in a greater response to H 2 at 2500 ppm compared with that of a rutile TiO 2 nanorod sensor by a factor of 1153. The response time was 21 s, mainly because the homojunction formed by the TiO 2 rutile and anatase phases increased the synergistic effect of the charge transfer and potential barrier between the two phases, resulting in the formation of more superoxide (O 2 - ) free radicals on the surface. Furthermore, the porous structure increased the surface area for H 2 adsorption. The TiO 2 -R/A-based sensor exhibited high selectivity, long-term stability, and a fast response. This study provides new insights into the design of commercially competitive hydrogen sensors.