Microporous zeolite modified yttria stabilized zirconia (YSZ) sensors for nitric oxide (NO) determination in harsh environments

This study is focused on development of a nitrogen monoxide (NO) sensor capable of operation in harsh environments, as exemplified by automotive exhaust streams. The basis of the sensor is a mixed potential response generated by exposure of gases to a platinum–yttria stabilized zirconia (Pt–YSZ) interface. The asymmetry between the two Pt electrodes on YSZ is generated by covering one of the electrodes with a zeolite, which helps promote the NO/NO2 equilibrium prior to the gases reaching the electrochemically active interface. The mixed potential generated is logarithmically related to NO concentration (0–1000 ppm) at temperatures between 500 and 700 °C, the optimum temperature being 500 °C. The microporosity of the zeolite makes it permeable to oxygen, thus, minimizing the interference to O2. The sensor shows interference from CO and NO2. Three sensor designs have been examined, including a planar design that can be packaged appropriately for surviving automotive exhaust streams. Automotive tests indicate that the sensor is capable of detecting NOx in engine exhausts.