Enhancement of gasochromic response to hydrogen of WO3 thin films by post-process modification and catalyst selection

The gasochromic properties of WO3 thin films deposited by electron beam evaporation were investigated, focusing on their structural, morphology and optical changes caused by heat treatment. Moreover, the influence of the thickness and type of catalyst on the gasochromic properties of WO3 was examined. X-ray diffraction measurements revealed that WO3 thin films annealed up to 473 K remained amorphous, whereas annealing at 673 K and above, initiated crystallization into a monoclinic structure. Gasochromic behaviour was observed in response to hydrogen exposure, with the most significant changes occurring in films annealed at 673 K with a thin adlayer of palladium catalyst. A gasochromic response of 1.84 was achieved for H2 concentration as low as 25 ppm. The process of gasochromic colouration was correlated with the changes of free charge carrier concentration calculated based on Drude free electron theory. XPS analysis confirms WO3 reduction under hydrogen exposure, validating proposed colouration mechanisms. These comprehensive findings offer insights into optimizing gasochromic thin films for various sensing applications.