Sol-Gel Pt-VO Films as Selective Chemoresistive and Optical H Gas Sensors.

In this work, VO (M1/R) thin films were exploited as H gas sensors. A flat film morphology, obtained by furnace annealing, was compared with a laser-induced nanostructured one. The combination of the environmentally friendly sol-gel approach with the ultrafast laser crystallization allows for significant reductions in energy consumption and related emissions during the fabrication of VO sensors. By decorating the sensors' surface with Pt nanoparticles (NPs), the sensor response was enhanced exploiting the hydrogen spillover effect. The Pt/VO sensors, tested at operating temperatures between 20 and 200 °C and for concentration of H from few ppm to 50000 ppm, offered a dual chemoresistive and optical sensing mode. Low operating temperatures of 150 °C were achieved, along with a detection limit as low as 2 ppm and a perfect baseline recovery. Both sensors guaranteed specific selectivity toward H, without response to NO or humidity, and long-term stability over 500 h. The H sensing mechanism, for both the monoclinic and rutile VO phases, was investigated through in operando X-ray Diffraction and in situ X-ray Photoelectron Spectroscopy tests. The interaction was found to be based on the reversible formation of HVO bronze, along with the reversible variations in the oxidation state of V.