Selective CO Detection by Using Indium Oxide-Based Semiconductor Gas Sensor.

From a screening test for the sensing properties of 26 single oxides, an In 2 O 3 sensor element was found to exhibit rather high sensitivity to both CO and H 2 in wet air at 300°C. In order to improve the selectivity to CO vs. H 2 , each of 33 metal oxides was added to In 2 O 3 . As a result, the addition of alkaline metal oxides was found to enhance markedly both sensitivity and selectivity to CO. Particularly, Rb 2 O (5 weight percent)-In 2 O 3 element showed the highest CO selectivity. It could detect 500 to 4000 ppm CO in wet air at 300°C satisfactorily.