Mixed-potential NH3 sensor with Fe2(MoO4)3 as the sensing electrode: Performance and mechanistic insights

Abstract

Ammonia (NH₃) is recognized as an important exhaled gas in patients with renal and hepatic diseases, with its concentration closely correlated to disease progression. Thus, detecting NH₃ in exhaled breath is crucial for self-diagnosis, disease monitoring, and large-scale screening of specific populations. In this study, we synthesized the sensing material iron molybdate (Fe₂(MoO₄)₃) and systematically investigated its performance in NH₃ detection. The results indicated that the sensor can realize the detection of 0.38 ppm NH₃, with the optimal sintering temperature identified as 550 °C and the optimal operating temperature as 475 °C. The response of the sensor to 5 ppm NH₃ is −24.3 ± 0.7 mV with response/recovery time of (55 ± 4)/ (86 ± 5) s. The X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscope (SEM) were applied to analysis the phase composition and morphology. The sensing mechanism was also discussed basing on the results of temperature-programmed desorption (TPD) and electrochemical impedance spectroscopy (EIS). Furthermore, the sensor exhibited reliable and stable performance across different test cycles, demonstrating its short-term and long-term stability.