NO₂ Sensing Capability of Pt-Au-SnO₂ Composite Nanoceramics at Room Temperature

Composite ceramics of metal oxides and noble metals have received much attention for sensing reducing gases at room temperature. Presently, composite ceramics of SnO₂ and noble metals have been prepared and investigated for sensing oxidizing NO₂ at room temperature. While dramatic increases in resistance were observed for both 1 wt% Pt-SnO₂ and 5 wt% Au-SnO₂ composite nanoceramics after being exposed to NO₂ at room temperature, the largest increase in resistance was observed for 1 wt% Pt-5 wt% -Au-SnO₂ composite nanoceramics among the three composites. The response to 0.5 ppm NO₂--20% O₂-N₂ was as high as 875 at room temperature, with a response time of 2566 s and a recovery time of 450 s in the air of 50% relative humidity (RH). Further investigation revealed that water molecules in the air are essential for recovering the resistance of Pt-Au-SnO₂ composite nanoceramics. A room temperature NO₂-sensing mechanism has been established, in which NO₂ molecules are catalyzed by Pt-Au to be chemisorbed on SnO₂ at room temperature, and desorbed from SnO₂ by the attraction of water molecules in the air. These results suggest that composite ceramics of metal oxides and noble metals should be promising for room temperature sensing, not only reducing gases, but also oxidizing gases.