Synergistic Enhancement on the Sensing Performance of Mixed Potential NH₃ Sensors by Fe and Mo Codoping into BiVO₄

Mixed potential ammonia (NH₃) sensors with the Fe- and Mo-codoped BiVO₄ sensing electrode and Ag reference electrode based on the yttria-stabilized zirconia solid electrolyte were developed. Fe- and Mo-doped BiVO₄ sensing materials were prepared using solution combustion synthesis and then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). It was observed that Fe doping could greatly improve the response rate, while Mo doping could enhance the response signal (ΔU) and sensitivity. Based on the optimal doping ratio of Fe and Mo each, the synergistic enhancement of the performance by Fe and Mo codoping was investigated. The sensor coated by BiV_0.75Fe_0.2Mo_0.05O_δ materials exhibited a prominent sensing performance to a low concentration of 10-50 ppm of NH₃ at 525 °C with the outstanding sensitivity of -148.988 mV/decade. Fe and Mo doping also improved the selectivity of the sensor to NH₃, with the relative deviations less than ±8% of other typical gases' interference including NO, NO₂, CO, CO₂, and CH₄. Besides, the sensor showed good resistance to fluctuations in the oxygen concentration and favorable stability against changes in the water vapor concentration. In addition, the sensor also exhibited good long-term stability. The mixed potential response mechanism was further discussed and analyzed through polarization curves as well as through gas chromatography and infrared absorption spectroscopy.