SrMoO4-based mixed-potential gas sensor for NH3 sensing in direct ammonia-fed fuel cells

Direct ammonia-fed fuel cells (DAFCs) are well known for sustainable energy production. However, the issue is a certain amount of unreacted NH3 fuel is obtained at the outlet. Thus, real-time monitoring and quantification are of utmost importance, nevertheless, this is troublesome due to the harsh thermodynamic conditions. This work aims to develop a mixed-potential sensing electrode for the detection of NH3 under reducing conditions (H2 atmosphere) at high temperatures. In this regard, a strontium molybdate (SrMoO4) sensing electrode (SE) is a potential solution due to its physical and chemical stability, along with its sensitivity to NH3 under reducing conditions. Therefore, an SrMoO4-based mixed-potential sensor is fabricated herein using yttria-stabilized zirconia (YSZ) as the electrolyte and platinum (Pt) as the reference electrode (RE) and is operated at 400–650 ℃. The maximum response exhibits about –21.57mV toward 80 ppm NH3 at 500 ℃. Further, the sensitivity is –17.19mV/decade towards 10–60 ppm and –45.33mV/decade towards 60–320 ppm NH3 under 75% H2 balanced by N2 at 500 ℃. The as-fabricated sensor also has good selectivity towards NH3 and good cross-sensitivity towards other interfering gases and is stable in long-term repeated operation. The direct current (DC) polarization curves and electrochemical impedance spectroscopy (EIS) results demonstrate the sensing mechanism in accordance with the mixed-potential theory.