General hydrogen gas sensing mechanism on SnO2 (110) surface based on DFT simulations

Abstract

With respect to the previous assumptions, the mechanism of metal oxide sensing towards hydrogen gas still remains controversial. Two H2 sensing mechanisms for metal oxide, oxygen-adsorption and oxygen-vacancy mechanism are generally accepted. In order to clarify the mechanism cleanly and take SnO2 (110) surface as a typical example, careful DFT simulations were carried out to investigate the interactions between small molecules (including H2, O2, and H2O) and metal oxide. We found that the dissociation of H2 can spontaneously take place on the SnO2 (110) surface. Based on the energy difference and transition state searching, the main barrier of H2 sensing lied in the dissociation of O2 on the surface. If there exists oxygen-vacancy on the surface, it would contribute to largely reduce the energy barrier of dissociation process of O2. Besides, the band alignments for different adsorption states were indicated. It suggested that the H2 sensing mechanism could be a mixed one including both oxygen-adsorption and oxygen-vacancy mechanism. At the end of this work, a modified band alignment as well as assumptive resistance change was provided, which was in line with previous experiment work. This work not only provided strong theoretical supports to previous assumptions, but also lightened the routes to design more outstanding H2 sensors.