Selective CO detection by using indium oxide-based semiconductor gas sensor

A compact, solid-state CO sensor has been in great demand for detecting incomplete combustion of gas appliances. Continuous CO monitoring of combustion exhaust can prevent a serious CO poisoning accident. From a screening test for the sensing properties of 26 single oxides, an In{sub 2}O{sub 3} sensor element was found to exhibit rather high sensitivity to both CO and H{sub 2} in wet air at 300 C. In order to improve the selectivity to CO vs. H{sub 2}, each of 33 metal oxides was added to In{sub 2}O{sub 3}. As a result, the addition of alkaline metal oxides was found to enhance markedly both sensitivity and selectivity to CO. Particularly, Rb{sub 2}O (5 weight percent)-In{sub 2}O{sub 3} element showed the highest CO selectivity. It could detect 500 to 4,000 ppm Co in wet air at 300 C satisfactorily.