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.