Cerium oxide (ceria) CO sensors exhibit fast, but smaller response than tin dioxide CO sensors; therefore, improvement in the response of ceria CO sensors is required. The effects of noble metal addition (Pt, Ag, Pd, or Au nanoparticles) on the response of ceria thick film CO sensors were investigated. The ceria thick film sensors with Au nanoparticles exhibited good response to CO; the addition of 5 wt% Au caused a 40 times increase in the sensor response. In contrast, no change in response was observed for the addition of Au to tin dioxide sensors. The response of the ceria sensors with Au decreased in the presence of propane or ethane compared to that without the noble metal. The sensors with Ag nanoparticles showed an increase response in the first measurement, but this response decreased with each measurement. Pd addition to the ceria sensors resulted in uneven responses and no increase in resistance was observed, in contrast to the tin dioxide sensors of which the resistance increases by Pd addition. In the case of the ceria sensors with Pt nanoparticles, the response was approximately the same as the sensors without noble metal nanoparticles.
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