A novel high-selectivity mixed potential ammonia gas sensor based on FeCr2O4 sensing electrode

Abstract

• Sensing material FeCr 2 O 4 was prepared using the polymer precursor method for fabricating sensing electrodes of mixed potential type NH 3 sensors based on yttria-stabilized zirconia (YSZ). • Sensing performance of the NH 3 sensors was strongly affected by sensing electrode thickness and operating temperature. • The sensor attached by FeCr 2 O 4 sensing electrode with a thickness of 98.95 μm demonstrated the largest response potential and the most outstanding sensitivity (-65.835 mV/decade) to 10–50 ppm NH 3 at 425℃. And the mixed potential has a linear relationship with the logarithm of NH 3 concentration. • The FeCr 2 O 4 /YSZ/Ag sensor exhibited excellent selectivity to NH 3 with the interference deviations of CH 4 , CO, CO 2 , NO, and NO 2 within ±10 %, good stability against oxygen concentration fluctuation and water vapor concentration change, and good long-term stability for 180 h. • According to the mixed potential mechanism, the sensitivity of the sensor was determined by the anodic reaction of NH 3 , the cathodic reaction of O 2 , as well as the non-electrochemical gas–solid heterogeneous catalytic reaction of NH 3 . Ammonia detection is of great significance for feedback control of urea injection in SCR system. In this paper, FeCr 2 O 4 sensing materials were prepared using the polymer precursor method used as the sensing electrode of mixed potential NH 3 sensors based on yttria-stabilized zirconia. The composition and structure of sensing electrodes were characterized using XRD and SEM. The effects of sensing electrode thickness and operating temperature on sensing performance were investigated. These related phenomena were ascribed to the adsorption and reactivity of NH 3 , as well as the competition between electrochemical catalytic reactions and gas–solid heterogeneous catalytic reactions. It was found that the sensor coated by FeCr 2 O 4 sensing materials with a thickness of 98.95 μm exhibited the largest response potential and the most outstanding sensitivity (-65.835 mV/decade) to 10–50 ppm NH 3 at 425℃. Furthermore, the sensor exhibited excellent selectivity to NH 3 with the interference deviations of CH 4 , CO, CO 2 , NO, and NO 2 within ±10 %, good stability against oxygen concentration fluctuation and water vapor concentration change, and good long-term stability for 180 h. Moreover, the sensing mechanism of the mixed potential sensor was discussed.