IMPROVED SENSITIVITY OF CUO-BATIO3 CAPACITIVE-TYPE CO2 SENSOR BY ADDITIVES

The sensitivity of a CuO-BaTiO3 capacitive-type CO2 sensor has been en hanced by the addition of metal or metal oxides except for Au, Fe2O3, CeO2 and Rh, whereas the operating temperature shifts slightly to a hi gher temperature and the response time is prolonged. In particular, th e change in capacitance caused by CO2 is markedly enlarged by the addi tion of ZnO, Bi2O3, SrO and Ag. Among these additives, silver is the m ost suitable from the viewpoints of sensitivity and operating temperat ure. The CuO-BaTiO3 plus Ag sensor can detect CO2 over four orders of magnitude of concentration from capacitance measurement. Furthermore, the positive effects of Ag addition on sensitivity are obtained only f or CO2 and CO. Therefore, CuO-BaTiO3 sensors exhibit extremely high se lectivity to CO2 detection in spite of the chemical stability of CO2. The improved sensitivity due. to Ag addition is reproducible and exhib its almost constant sensitivity to 5000 ppm CO2 over a period of 30 da ys.