Sub-ppb SO2 gas sensor based on NASICON and LaxSm1-xFeO3 sensing electrode

A NASICON-based mixed-potential gas sensor utilizing the perovskite-type orthoferrite LaxSm1-xFeO3 (x = 0.2, 0.4, 0.5, 0.6, 0.8) sensing electrode (SE) was designed for SO2 detection. The research mainly put emphasis on the effect of different La3+ doping ratios in LaxSm1-xFeO3 on the sensing characteristics, and the highest response value (-86.5 mV) to 1 ppm SO2 was observed for the sensor using La0.5Sm0.5FeO3-SE. The response value of the fabricated sensor displayed segmentally linear relationship with the logarithm of SO2 concentration in the ranges of 0.005-0.2 ppm and 0.2-5 ppm, and the slopes were −8 and −86 mV/decade, respectively. Otherwise, the low detection limit of the present sensor even could reach to 5 ppb with an accurate response value (-8.4 mV). Meanwhile, the sensor also showed good repeatability, long-term stability and selectivity toward other interfering gases. Furthermore, the electrochemical impendence curves indicated the reason that the sensor attached with La0.5Sm0.5FeO3-SE displayed the higher response values than the other sensors. The result indicated that differences of electrocatalytic activity was caused by diverse La3+ doping content in sensing electrode. The sensing mechanism related to the mixed potential was demonstrated by the polarization curve.