Effect of Noble Metal Doping and Operating Temperatures on the Optical Hydrogen Sensing Properties of Sol–Gel Grown WO3 Thin Films

Abstract

In this work, a detailed study has been carried out to understand the gasochromic properties of tungsten oxide at different operating temperatures, sol (low, medium, high), and doping concentrations. Similarly, the hydrogen sensing results are corroborated with material characterization to get more insight into the gasochromic performance of the prepared samples. In addition to this, the effect of noble metal (Pt, Pd) doping on the gasochromic performance has been discussed with a focus on X-ray photoelectron spectroscopy (XPS) and Raman studies, which is lacking in the literature. The Pt- and Pd-doped tungsten oxide thin films were prepared by the sol–gel method and spin-coated onto glass substrates. A detailed Raman spectroscopy of the samples reveals tungsten’s coexistence in monoclinic crystalline and hydrous phases. The surface morphology and chemical compositions of the samples were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and XPS. The ultra violet-visible-near infra-red (UV–VIS–NIR) transmittance results show that gasochromic response increases significantly with an increase in operating temperature. Pt-doped sample prepared from moderate sol concentration exhibited a higher transmittance change of 22% for 4% hydrogen purge at an operating temperature of 70 °C. The response and recovery times measured were less than 40 s. Pt-doped samples showed better gasochromic response than Pd-doped samples due to higher catalytic activity of PtO:Pt compared to PdO:Pd. The sample had a lower detection limit of 0.01% at temperatures between 50 °C and 100 °C and did not show any cross sensitivity toward other gases.