Highly selective H2S gas sensor based on WO3-coated SnO2 nanowires

The enhancement of the H2S gas-sensing performance of SnO2 nanowires is vital for practical application. In this study, H2S gas sensors based on WO3-coated SnO2 nanowires were fabricated through a two-step process, namely, the chemical vapor deposition of SnO2 nanowires and then coating with WO3 by sputtering method. The morphology and crystal structures of the SnO2 nanowires coated with WO3 were investigated by field-emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The H2S gas-sensing properties of the fabricated sensors were tested at temperatures of 150-250 degrees C. The SnO2 nanowires coated with 5 nm WO3 showed the best response to low-concentration H2S gas (0.1-1 ppm). At the optimal working temperature of 200 degrees C, the sensor had a sensitivity of 177 toward 1 ppm H2S with good selectivity over the contamination of NO2, NH3, H-2, and CO gases. We also discussed the gas-sensing mechanism of the fabricated sensor based on the n-n heterojunction between n-type SnO2 and n-type WO3, which formed a thick depletion layer and thus enhanced the sensitivity to H2S.