Compact Yttria-Stabilized Zirconia Based Total NO Sensor with a Dual Functional Co₃O₄/NiO Sensing Electrode

Yttria-stabilized zirconia (YSZ) based potentiometric gas sensors have been widely utilized for detecting NO (NO and NO₂). Nevertheless, it is still remains challenging issue for YSZ-based sensors to sense total NO due to the opposite response signals to NO and NO₂. Herein, we report an efficient strategy to sense total NO at high temperature (above 300 °C) by designing a dual functional sensing electrode (SE); namely, the SE will simultaneously convert NO (in NO mixture) to NO₂ and electrocatalyze all of the obtained NO₂ to generate the response signal of total NO. In comparison with those previously reported total NO sensors, the proposed total NO sensor will be featured with a simplified sensor configuration and desirable long-term stability. To confirm the practicability of the proposed strategy, the NO conversion rate of several metal oxides and their composites have been measured and it turns out that the Co₃O₄/NiO shows relatively high NO conversion rate. Further study indicates a YSZ-based sensor consisting of (Co₃O₄ + 20 wt % NiO)-SE and Mn-based RE demonstrates satisfactory performance in detecting total NO. For instance, analogous response magnitude to NO and NO₂ as well as the mixture of NO/NO₂ (within 35 ppm) is witnessed for the sensor; particularly, the sensor gives acceptable stability and response/recovery rate at the operating temperature of 500 °C within the examined period. In summary, the use of dual functional SE (e.g., Co₃O₄/NiO composite SE) indeed addressed those issues of concern in monitoring the level of total NO and has provided a promising alternative way for designing future high-performance total NO sensor.