H2S sensing properties of added copper oxide in WO3

We study Hydrogen sulfide gas detection properties of pure and 1% copper oxide added WO3 thin films The spin coated deposits on alumina substrates were annealed at 500 degrees C for 1 hour in order to improve the crystallinity of the films. The sensitivity of pure tungsten oxide is poor even at temperatures of about 100 degrees C but the doped samples exhibit good response to H2S gas. Our data show sensitivity of about 1500 in 10 ppm diluted gas in air at 100 degrees C. The films are sensitive to the gas even at 250 ppb (sensitivity about 2) H2S concentration at 100 degrees C but with rather long recovery time. Crystal structure, morphology and chemical composition of samples were studied by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses. We suggest that Cu2O dopants dissociate H2S molecules and spillover of the hydrogen atoms onto the cracked WO3 surface. The reaction of dissociated H2S with adsorbed oxygen is the main reason for reduction of resistivity.