CO Response Characteristics of NiFe₂O₄ Sensing Material at Elevated Temperature

Abstract

A potentiometric sensor based on YSZ and NiFe2O4 sensing electrode was developed for CO detection. NiFe2O4 was prepared by sol-gel method and calcined at 900°C for 6 h. NiFe2O4-SE was prepared by screen printing and sintered at 1150°C for 3 h. NiFe2O4 powder and NiFe2O4-SE were confirmed to be pure phase after XRD characterization. The SE presents a porous network structure based on SEM analysis. The CO response characteristics of the sensor were evaluated between 650°C and 750°C, and it was found that it had the largest sensitivity with the slope of −47.57 mV/decade at 700°C and could detect a minimum CO concentration of 20 ppm. At 700°C, the sensor had relatively short response and recovery times of 21 s and 52 s for 320 ppm CO, respectively. The response values varied almost linearly with the logarithm of CO concentration at each operating temperature, which is consistent with mixed-potential mechanism verified by polarization curves. It showed tiny cross sensitivities to NOx, but non-negligible C3H8 cross sensitivity. The sensor also displayed slight signal drifts in weekly tests in eight weeks, which showed that NiFe2O4-SE had a good long-term stability.