CO response of a nanostructured SnO2 gas sensor doped with palladium and platinum

In this paper, we show the influence of humidity on the sensitivity for CO sensing of the nanoparticular SnO2 sensors at an operating temperature of 450 degreesC. Three different sensors have been studied: un-doped sensors and doped sensors with two doping agents palladium and platinum. It is well known that the resistance of the sensitive layer is largely modified by doping. This study demonstrates that un-doped sensors show under CO a sensitivity less important in humid air than in dry air. Doped sensors display a very different behavior. Indeed, in dry air, a high sensitivity is observed, characterized by an increase in the resistance of the sensitive layer whereas in humid air (>10% RH) a high sensitivity is also observed but characterized by a decrease in the resistance of the sensitive layer. In between, a point of zero sensitivity is found. These results carry out the presence of unexpectedly different electrochemical operating mode for CO sensing according to the humidity content. (C) 2004 Elsevier B.V. All rights reserved.