Enhancing ammonia sensing performance of Ag2MoO4-based mixed-potential sensor by introducing ionic and electronic conductance

Abstract

The breath ammonia detection is crucial for the evaluation of the pathological state. Among the existing ammonia detection technologies, the mixed potential sensor exhibits promising potential owing to its high stability, good selectivity and small size. However, it remains challenging in application due to its insufficient limit of detection (LOD). To improve the performance of such sensor, a novel sensing material Ag2MoO4 was synthesized in this work. The electrode morphology was tuned for optimum performance by adjusting the sintering temperature. The response to 5 ppm NH3 at 425 °C is about −29.86 mV with response/recover times of 105/96 s and sensitivity of −49.55 mV/decade. In addition, the sensor exhibits good selectivity and outstanding detection capability of trace-level NH3 as low as 400 ppb. High concentrations of water vapor and CO2 can greatly affect its performance, but it can be easily eliminated by a filter. The research of its sensing mechanism reveals that Ag2MoO4 has both ionic conductance and electronic conductance, which transforms the electrochemical reaction site from two-dimensional three-phase boundaries (TPB) to a three-dimensional one distributed within the sensing material. Specifically, the sensor shows excellent NH3 detection ability with the number of reaction sites increases.