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The NH 3 sensitivity of a potentiometric YSZ-based planar sensor utilizing ZnFe 2 O 4 sensing electrode (SE) was tuned by sputtering Au on the SE. ZnFe 2 O 4 was prepared by sol-gel method and calcined at 900 °C. ZnFe 2 O 4 -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 ZnFe 2 O 4 -SE. The response characteristics of the sensor to 5–80 ppm NH 3 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 NH 3 was −42.3 mV, and it has relatively short response and recovery time of 25 s and 49 s for 80 ppm NH 3 , respectively. It could even displayed a considerable signal for 5 ppm NH 3 at each temperature. The oxygen concentration had non-negligible influence on the NH 3 response signal. It showed tiny cross sensitivities toward NO x and C 3 H 8 , 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 ZnFe 2 O 4 had a good long-term stability. • ZnFe 2 O 4 was used as NH 3 sensing electrode for potentiometric gas sensor for the first time. • The response signal and response/recovery rate were greatly enhanced after the ZnFe 2 O 4 -SE was tuned by sputtering Au. • The sensor displays a considerable signal for 5 ppm NH 3 between 650 °C and 750 °C. [ABSTRACT FROM AUTHOR]