NO and NO(2) Sensing Properties of WO(3) and Co(3)O(4) Based Gas Sensors

Semiconductor-based gas sensors that use n-type WO(3) or p-type Co(3)O(4) powder were fabricated and their gas sensing properties toward NO(2) or NO (0.5–5 ppm in air) were investigated at 100 °C or 200 °C. The resistance of the WO(3)-based sensor increased on exposure to NO(2) and NO. On the other hand, the resistance of the Co(3)O(4)-based sensor varied depending on the operating temperature and the gas species. The chemical states of the surface of WO(3) or those of the Co(3)O(4) powder on exposure to 1 ppm NO(2) and NO were investigated by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. No clear differences between the chemical states of the metal oxide surface exposed to NO(2) or NO could be detected from the DRIFT spectra.