A Novel Highly Sensitive NO₂ Sensor Based on Perovskite Na_0.5+xBi_0.5TiO_3-δ Electrolyte

NO_x is one of dangerous air pollutants, and the demands for reliable sensors to detect NO_x are extremely urgent recently. Conventional fluorite-phase YSZ used for NO_x sensor requires higher operating temperature to obtain desirable oxygen ion conductivity. In this work, perovskite-phase Na_0.5Bi_0.5TiO₃ (NBT) oxygen conductor was chosen as the solid electrolyte to fabricate a novel highly sensitive NO₂ sensor with CuO as the sensing electrode and Pt as reference electrode. Na dopped Na_0.5Bi_0.5TiO₃ greatly improved the sensing performance of this sensor. The optimal sensor based on Na_0.51Bi_0.50TiO_3-δ exhibited good response-recovery characteristics to NO₂ and the response current values were almost linear to NO₂ concentrations in the range of 50-500 ppm at 400-600 °C. The response current value towards NO₂ reached maximum 11.23 μA at 575 °C and the value on NO₂ is much higher than other gases (CH₄, C₂H₄, C₃H₆, C₃H₈, CO), indicating good selectivity for detecting NO₂. The response signals of the sensor were slightly affected by coexistent O₂ varying from 2 to 21 vol% at 575 °C. The response current value decreased only 4.9% over 2 months, exhibiting the potential application in motor vehicles.