Mixed potential NOx sensors using thin film electrodes and electrolytes for stationary reciprocating engine type applications

Mixed potential sensors using dense, thin film metal oxide working electrodes, Pt counter electrodes, and thin film YSZ electrolytes on Al2O3 polycrystalline and sapphire substrates were prepared and studied between 450 and 650 °C. Their response to NO, NO2, CO, and C1 and C3 hydrocarbons in 10.4% O2/N2 balance and in air atmospheres was characterized. The lanthanum chromite-based sensors showed preferential sensitivity to NO2 with cross sensitivity to CO and non-methane hydrocarbons such as C3H6 and C3H8 with the highest NOx sensitivity and minimal CO/HC cross sensitivity exhibited by a sensor prepared with a La0.8Sr0.2CrO3 working electrode. Studies of the Mg-doped LaCrO3 devices conducted for up to 800 h at 600 °C showed minimal aging in these devices. In contrast, sensors fabricated with spinel NiCr2O4 or ZnFe2O4 working electrodes showed preferential sensitivity to HCs and minimal sensitivity to NO2. Sensors fabricated with Y0.16Tb0.3Zr0.54O2−∂ working electrodes required operating temperatures in excess of 600 °C and, like the spinels, showed minimal NOx sensitivity. A prototype three-electrode mixed potential device for the detection of multiple gases was also demonstrated. The use of a heated Pt black pre-catalyst upstream to the sensor was demonstrated to effectively remove the CO and hydrocarbon response.