Hydrogen sensing mechanism of Ru-loaded WO3 nanosheets

Gas sensors based on tungsten trioxide (WO3) have been greatly investigated and successfully commercialized. Generally, pristine WO3 is quite sensitive to oxidizing gases such as nitrogen dioxide and ozone. However, when noble metals dispersed on the surface, WO3 could become very sensitive to reducing gases, such as hydrogen (H-2) and acetone. Notably, the sensitization mechanisms are varied with different noble metals. Recently, ruthenium (Ru) has been found to be a very effective sensitizer, which enable WO3 to be sensitive to reducing gases. In the present study, Ru loaded WO3 (Ru-WO3) nanosheets were prepared and the sensitization mechanism was investigated under both dry and humid conditions. The basic sensing mechanism was revealed by the oxygen adsorption and surface catalytic activities. According to our results, it was found that Ru loading can greatly promote the sensor response of WO3 to H-2, even with a very small amount. Ru-WO3 could also respond to H-2 in both oxygen containing and non-oxygen background, nevertheless, the basic sensing processes were significantly different. With presence of humidity, the sensitization mechanism of Ru become different from that under a dry condition.