Improvement in Gasochromic Properties of Tungsten Trioxide Using Optimized Pd Doping

Abstract

Tungsten oxide layers are important structures in gasochromic and optical hydrogen sensing devices. In the present study, these layers were constructed using the sol-gel method and spin-coating deposition technique. WO layers were coated with palladium using the same method to investigate the catalytic role of palladium on the surface of the layers. This catalyst was used to coat the WO layers in the form palladium chloride using different concentrations of palladium. The layers were heated at different temperatures to study the gasochromic properties of the WO layer in different crystalline and amorphous phases. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), xray diffraction (XRD) and spectrophotometer analysis were used to investigate the surface morphology, structure of layers and size of the nanoparticles. When the colored glass was exposed to air, the sensor returned to its initial transmission state. The results of XRD spectral analysis showed that the layers commenced crystallization at 300°C and were completely crystallized at 500°C. The effects of temperature and catalyst concentration are investigated simultaneously. Optimal conditions were achieved at 300°C and for the 0.05M concentration of palladium chloride solution. Under this condition, after applying 2.7% hydrogen gas, the transmission change of the sample (ΔT1%=Ta-Tb , where Ta is initial Original Research Article Physical Science International Journal, 4(3): 372-383, 2014 373 transmission and Tb is coloring state of glass) was 47% and the response time was 3s. The transmission change (ΔT2%=Tc-Tb , where Tc is bleaching and Tb is coloring state of glass) and recovery time were 22% and 25s, respectively, after exposure of the sensor to air.