Ultrasensitive Gas Sensor Using Co3O4-Modified SnO2

Abstract

SnO2 powder was loaded with 0-5% Co3O4 by mass by a ball milling method. The resulting composites were screen printed onto a substrate to test the sensing properties to CO and H2. It was found that the sensor response, defined as the ratio of electrical resistance in air to that in gas, was greatly promoted with 0.5 or 1.0% Co3O4 loading, while further loadings (3 or 5%) gave an adverse effect. For the 1% Co3O4-loaded device, for example, the responses to 100, 50 and 10 ppm CO in air were as large as 375, 181 and 23 at 250 °C, respectively, and those to 50, 10 and 1 ppm H2 in air were 568, 181 and 53 at 300 °C, respectively. The electrical resistance in air increased significantly with increasing Co3O4 loading, indicating an electronic interaction between Co3O4 and SnO2. The change of the electronic interaction with a change in the redox state of Co3O4 appears to be an origin of the ultra high sensitivity to CO and H2.