Gas sensing selectivity of hexagonal and monoclinic WO3 to H2S

Hexagonal and monoclinic tungsten oxide (h- and m-WO3) samples were produced by annealing hexagonal ammonium tungsten bronze, (NH4)0.07(NH3)0.04(H2O)0.09WO2.95 at 470 and at 600 °C, respectively. Their structure, composition and morphology were analyzed by XRD, Raman, XPS, 1H-MAS NMR and SEM. In order to study the effect of crystal structure on the gas sensitivity of tungsten oxides, h- and m-WO3 were tested as gas sensors to CH4, CO, H2, NO and H2S (1000 and 10 ppm) at 200 °C. Monoclinic WO3 responded to all gases, but its gas sensing signal was two magnitudes greater to 10 ppm H2S than to other gases, and it also detected H2S even at 25 °C. Hexagonal WO3 responded only to 10 ppm H2S. Its sensitivity was smaller compared to m-WO3, however, the response time of h-WO3 was significantly faster. The gas sensing tests showed that while m-WO3 had relative selectivity to H2S in the presence CH4, CO, H2, NO; h-WO3 had absolute selectivity to H2S in the presence these gases.

Hexagonal WO3 has absolute selectivity to sensing H2S in the presence CH4, CO, H2, NO.Figure optionsDownload as PowerPoint slide