High sensitivity and fast response sensor based on sputtering Au tuned ZnFe2O4-SE for low concentration NH3 detection

Abstract The NH3 sensitivity of a potentiometric YSZ-based planar sensor utilizing ZnFe2O4 sensing electrode (SE) was tuned by sputtering Au on the SE. ZnFe2O4 was prepared by sol-gel method and calcined at 900 °C. ZnFe2O4-SE was prepared by screen printing and sintered at 1100 °C for 3 h. SEM results show that Au is uniformly distributed in the network structure of the ZnFe2O4-SE. The response characteristics of the sensor to 5-80 ppm NH3 were evaluated between 650 °C and 750 °C, and it was found that the response rate and response signal increased significantly after gold sputtering on SE. The performance improvement by gold sputtering may originate from enhanced catalytic activity of the anodic electrode reaction, which was observed by the polarization curve test. At 700 °C, the sensor exhibited the largest sensitivity with the slope of -31.3 mV/decade, and its response to 80 ppm NH3 was -42.3 mV, and it has relatively short response and recovery time of 25 s and 49 s for 80 ppm NH3, respectively. It could even displayed a considerable signal for 5 ppm NH3 at each temperature. The oxygen concentration had non-negligible influence on the NH3 response signal. It showed tiny cross sensitivities toward NOx and C3H8, but weak CO cross sensitivity. When the water vapor concentration is within 10%, the water vapor has a small influence on the response signal. The sensor also displayed slight signal drifts in weekly tests in six weeks, which showed that ZnFe2O4 had a good long-term stability.