Sensing properties of Au-loaded SnO2–Co3O4 composites to CO and H2

Two kinds of SnO2–Co3O4 composites, SC1 and SC50, the Co3O4 contents of which were 1 and 50 mass%, respectively, were loaded with small amounts of Au (0.05, 0.5 and 1 mass%). The thick film device using SC1, characterized by high sensitivity to both CO and H2 at 250 °C, was found to be made more sensitive without significant alterations of selectivity between CO and H2 as the amount of Au-loaded increased up to 0.5%, while the addition of 1 mass% Au degraded the sensing properties seriously. Similar promoting effects of Au were recognized for the SC50-based devices, which were p-type semiconductors responding fairly selectively to CO over H2 at 100 °C. The promoting effects of Au were discussed briefly based on the behavior of electrical resistances of the Au-loaded devices.