High NH3 selectivity of NiFe2O4 sensing electrode for potentiometric sensor at elevated temperature.

NiFe 2 O 4 was synthesized using sol-gel method for sensing electrode material of YSZ based ammonia sensor. NiFe 2 O 4 -SEs sintered at 1100 °C, 1150 °C and 1200 °C were characterized by XRD, the BET method and ESEM. By testing the NH 3 response of different sensors at 650 °C, it was observed that the 1150 °C sintered sensor had the largest response value (−104.3 mV for 320 ppm NH 3) and the highest sensitivity (−77.56 mV/decade), which were related to the most TPB sites and the moderate gas phase catalytic reaction. The response values of the sensor varied almost linearly with the logarithm of 20–320 ppm NH 3 at 600–750 °C, which was consistent with mixed-potential mechanism testified by polarization and EIS tests. When the oxygen concentration was at 7–10 vol %, its effect on the response value was within 3%. When the water vapor concentration was 3, 6 and 9 vol %, the ammonia response value was 95.1%, 92.9% and 88.7% of the values when there was no water vapor, respectively. The sensor showed very weak cross sensitivities to NO x , but non-negligible SO 2 cross sensitivity. It also displayed slight signal drifts in weekly tests in eight weeks, which showed that the sensor attached with NiFe 2 O 4 -SE has a good long-term stability. Image 1 • NiFe 2 O 4 was firstly used as sensing electrode of potentiometric NH 3 sensor based on the proposed novel concept. • NH 3 sensor based on NiFe 2 O 4 -SE exhibits good selectivity and long term stability. • NiFe 2 O 4 material has a good application prospect for NH 3 detection in diesel vehicle exhaust. [ABSTRACT FROM AUTHOR]