Gas sensing properties of amperometric NH3 sensors based on Sm2Zr2O7 solid electrolyte and SrM2O4 (M = Sm, La, Gd, Y) sensing electrodes

The work showed a novel amperometric NH3 sensor based on SrM2O4 (M = Sm, La, Gd, Y) with CaFe2O4 type structural sensing electrode. A distinct B-site strategy was developed to prepare a series of semiconductor oxides SrM2O4 (M = Sm, La, Gd, Y) to establish the relationships between the band structure and sensing properties of the optimized sensing electrode. The structural analyses carried out by X-ray diffraction, scanning electron microscopy and Mott-Schottky curves confirm that four metal oxides SrM2O4 (M = Sm, La, Gd, Y) are all n-type semiconductors, and a preferential sensing mechanism of NH3 sensor was proposed by the combination of mass spectrometry track. The electrochemical results indicate that NH3 sensing properties are closely related to the band structure of the metal semiconductor oxides. Compared with the conduction band obtained from Mott-Schottky curves, it is the most negative for SrM2O4 sensing electrode, suggesting that electrons are easier to overcome energy barriers over SrM2O4. Consequently, the NH3 sensor with SrM2O4 sensing electrode exhibits high sensitivity, quicker response/recovery speed, excellent selectivity and stability compared to other three sensors, exhibiting a great application prospects for SrM2O4 sensing electrode used in the automotive equipments.