Dense LaSrMnO3 composite electrodes for NOx sensing

Impedancemetric NOx sensors composed of dense La0.8Sr0.2MnO3 (LSM) and LSM composite electrodes were evaluated based on the electrical response, sensitivity, and selectivity to NOx at operating temperatures ranging from 575 - 675 °C under dry and humidified gas environments. The composite electrodes investigated containing 10 wt% Au or 30 wt% Y2O3-ZrO2 (YSZ) were accompanied by a porous YSZ electrolyte. The LSM-Au electrodes demonstrated a higher response to NOx with limited cross-sensitivity to water, in comparison to LSM and LSM-YSZ sensing electrodes. However, the response and recovery time of LSM and LSM-YSZ based sensors was more rapid than that of LSM-Au based sensors. The rate limiting mechanism effecting sensor behavior appeared to be oxygen reduction regardless of the sensor electrode. Transport of atomic oxygen was an additional rate limiting step for the LSM and LSM-YSZ based sensors. Cross-sensitivity analysis indicated the LSM-Au based sensors were more selective to NOx, in comparison to CO, CO2 and CH4. Overall, the 10 wt% Au addition to LSM appeared to enhance sensor sensitivity to NOx by enabling NOx reactions to proceed more readily.