Improvement in response of resistive oxygen sensor based on ceria–zirconia thick film with Pt catalyst on surface

A resistive oxygen sensor based on ceria doped with 10 mol% zirconia can distinguish between fuel-rich and lean conditions in the case of a model exhaust gas in an equilibrium state. However, the response is unpredictable in a model exhaust gas in a nonequilibrium state. In this study, we investigated the response of an oxygen sensor in a model exhaust gas in a nonequilibrium state. The following problems were identified in relation to the ceria–zirconia sensor. First, in a nonequilibrium state, the resistive oxygen sensor indicated a propane lean condition when in fact the system was in a propane rich condition; under the same conditions, an electromotive force sensor based on an oxide ion conductor indicated a propane rich condition. Second, in an equilibrium state, the response of the resistive sensor, which was heated by a self-heater at 600 °C, was very slow in indicating a change from lean to rich conditions. In order to solve these problems, we fabricated a resistive oxygen sensor including a Pt catalyst on the surface by a simple new process and investigated its response. Through optimization of the Pt content, we were able to resolve the first response problem. That is, the sensor could distinguish between rich and lean conditions in a nonequilibrium state. Furthermore, the response speed was also improved by the Pt catalyst.