Dynamic Reaction Mechanism of P-N-Switched H2-Sensing Performance on a Pt-Decorated TiO2 Surface.

Pt decoration is known to be one of the most promising strategies to enhance the performance of TiO2 hydrogen gas sensors, while the effect of Pt-decorating concentration on the sensing performance of TiO2 and the specific interaction between Pt and TiO2 have not been fully investigated. Here, a series of TiO2 nanoarray thin films with differing amounts of Pt decorated (Pt/TiO2) is fabricated, and the H2-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 H2 concentration: resistance increases in low H2 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 TiO2 surface. The preference for H2 adsorption and splitting between Pt and TiO2 is established by DFT calculations. Humidity brings preferential adsorption of H2O on the surface of Pt, which affects the following adsorption and splitting of H2, thus resulting in a P-N switch of the sensing performance. The detailed dynamic reaction process is described according to the findings.