NO and NO2 Sensing Properties of WO3 and Co3O4 Based Gas Sensors

Abstract

Semiconductor-based gas sensors that use n-type WO3 or p-type Co3O4 powder were fabricated and their gas sensing properties toward NO2 or NO (0.5–5 ppm in air) were investigated at 100 °C or 200 °C. The resistance of the WO3-based sensor increased on exposure to NO2 and NO. On the other hand, the resistance of the Co3O4-based sensor varied depending on the operating temperature and the gas species. The chemical states of the surface of WO3 or those of the Co3O4 powder on exposure to 1 ppm NO2 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 NO2 or NO could be detected from the DRIFT spectra.

Ultrasensitive WO 3 gas sensors for NO 2 detection in air and low oxygen environment

“…Several types of NO x gas sensors have been developed and commercialised including metal oxide semiconductors and solid electrolytes [3][4][5][6]. Among metal oxide semiconductors, specifically those based on WO 3 are of particular interest due to their structural simplicity, high sensitivity, low cost and potential durability for operation under extreme conditions [7][8][9]. Nanostructured metal oxide semiconductors are widely used for the fabrication of sensors for the detection of both oxidising (such as NO 2 ) and reducing gases (such as CO) [10].…”

Preparation of WO₃ nanoplatelet-based microspheres and their NO₂ gas-sensing properties

“…These sensor responses are much larger than that of the sensor element comprising commercial WO 3 particles, measured under the same conditions (S = 19.2 for 1 ppm NO 2 exposure at 200°C) or that of a sensor element with WO 3 ·xH 2 O-based microspheres (S = ³30 for 1 ppm NO 2 exposure at 200°C). 7) Since the obtained particles consist of nanoplatelets, the specific surface areas of the samples are expected to be larger than those of commercial WO 3 or WO 3 ·xH 2 O-based microspheres. These results suggest that the sensing layer of the sensor element employing these particles has an effective microstructure for NO 2 gas sensing.…”

Effect of Noble Metal Addition on Co3O4-Based Gas Sensors for Selective NO Detection

“…(7)(8)(9)(10)(11) Among the metal oxides, n-type tungsten oxide (WO 3 ) appears to be a promising material for use in a NO gas sensor. (8,9) In a previous publication, we reported on the reliable response of a p-type cobalt oxide (Co 3 O 4 ) gas sensor to NO gas at 0.5-5 ppm in air.…”

“…(8,9) In a previous publication, we reported on the reliable response of a p-type cobalt oxide (Co 3 O 4 ) gas sensor to NO gas at 0.5-5 ppm in air. (10) Furthermore, because that Co 3 O 4 gas sensor showed a low resistance of below 1 kΩ, the peripheral circuit used to measure the sensor resistance does not require a large resistance, reducing the device cost. However, to the best of our knowledge, the Co 3 O 4 -based gas sensor's responses to NO gas at several hundred ppb have not been studied.…”

“…(12) Moreover, the Co 3 O 4 -based gas sensor in our previous publication showed a low response even at 0.5 ppm NO, and responses to NO gas at several hundred ppb have not been studied. (10) Therefore, the addition of a noble metal to these metal oxide semiconductors is critical for improving the sensitivity and selectivity of these gas sensors. (13,14) We reported that the NO gas sensing properties of the Pd-loaded Co 3 O 4 sensor with 0.1-30 wt% Pd content were estimated and the sensor with 10 wt% Pd content showed a high response and signal-to-noise ratio.…”