Dynamic Reaction Mechanism of P-N-Switched H-Sensing Performance on a Pt-Decorated TiO Surface.

Pt decoration is known to be one of the most promising strategies to enhance the performance of TiO hydrogen gas sensors, while the effect of Pt-decorating concentration on the sensing performance of TiO and the specific interaction between Pt and TiO have not been fully investigated. Here, a series of TiO nanoarray thin films with differing amounts of Pt decorated (Pt/TiO) is fabricated, and the H-sensing performance is evaluated. A switch in the response from P-type to N-type is observed with increasing Pt decoration. The response additionally depends on the H concentration: resistance increases in low H concentrations and decreases in hydrogen concentrations higher than 40 ppm. This is explained by the competitive adsorption of hydrogen between the Pt nanoparticles (Pt NPs) and the exposed TiO surface. The preference for H adsorption and splitting between Pt and TiO is established by DFT calculations. Humidity brings preferential adsorption of HO on the surface of Pt, which affects the following adsorption and splitting of H, thus resulting in a P-N switch of the sensing performance. The detailed dynamic reaction process is described according to the findings.