Hydrogen Sensor Based on Pd: WO3 Films Prepared by Sol- gel Process

It is well known that detection and leak control of gases such as nitrogen oxides, Hydrogen and carbon monoxide are crucial to reduce the noxious effects on environment and human beings. In case of environmental monitoring, the threshold limit value for Hydrogen is 4%. Among semiconductors WO3 based sensor has been studied extensively. WO3 seems to be the most promising material for sensing the above mentioned gases [1]. Metal additives such as Pd as a catalyst promotes Hydrogen sensing in low concentrations at room temperature by increasing sensitivity and selectivity as well as reducing the response and recovery times. On these systems, Hydrogen dissociates and atomic hydrogen spills over on the oxide supports. An approach is to incorporate the catalyst in the form of metallic particles within the WO3 film. This is achieved using sol-gel processing which allows the inclusion of metallic particles with nanosized dimension, narrow particle size distribution and adjustable metal loading [2]. In the present work, Tungsten trioxide films has been prepared from peroxopolytungstic acid (P-PTA) sols as a precursor and we added PdCl2 to tungsten sol in different weight ratios of Pd:WO3<=0.01 wt% and deposited on alumina substrates by spin coating method. Then the films were annealed at 500 0C. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) were employed to analyze the structure and morphology of the fabricated thin films. The operation of most semiconductors is based on a reversible change of electrical conductivity. Change of conductivity is due to physical and chemical reaction of absorbed gas species on the sensitive surface. We emphasized on the Hydrogen sensitivity of WO3 and worked on its response and recovery times and also on operating temperatures which is so important to make a low power consumption sensor and be environmental friendly. Also we planed to make a sensor with low cost for fabrication by sol gel process which has long term chemical stability