Abstract
NOx is one of dangerous air pollutants, and the demands for reliable sensors to detect NOx are extremely urgent recently. Conventional fluorite-phase YSZ used for NOx sensor requires higher operating temperature to obtain desirable oxygen ion conductivity. In this work, perovskite-phase Na0.5Bi0.5TiO3 (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 Na0.5Bi0.5TiO3 greatly improved the sensing performance of this sensor. The optimal sensor based on Na0.51Bi0.50TiO3−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.
Highlights
As one of the most dangerous air pollutants NOx has attracted great attention of environmentalists and researchers during the past decades due to its severe effect on human health and environment[1]
Based on the principle of amperometric-type NO2 sensor, the following electrochemical reactions occurred at three phase boundary (TPB) of cathode and the anode (Pt reference electrode, RE) have been proposed[4, 5]: (SE)Cathode: NO2 + 2e− → NO + O2−
In whole process of the electrode catalytic reaction, the rate-determining step is closely related to the adsorption of the sensing electrode towards NO2 at TPB, the formation rate of O2−, and the transmission speed of O2− generated at the cathode that is depended on the electrolyte material
Summary
As one of the most dangerous air pollutants NOx has attracted great attention of environmentalists and researchers during the past decades due to its severe effect on human health and environment[1]. Electrochemical sensor is one of reliable appliance which has drawn considerable attention for its advantage to detect NOx accurately in high temperature and harsh operation of exhaust gases[1, 2]. The amperometric-type sensor can realize fast detection to NOx concentration through monitoring in-suit current signal[3, 4]. This sensor mainly consists of solid electrolyte, sensing electrode and reference electrode, whereas the matching of solid electrolyte and sensing electrode would directly impact the sensing performance of NO2 sensor. Based on the principle of amperometric-type NO2 sensor, the following electrochemical reactions occurred at three phase boundary (TPB) of cathode (sensitive electrode, SE) and the anode (Pt reference electrode, RE) have been proposed[4, 5]:. Compared to YSZ, perovskite oxide (ABO3) can adapt to variation by different substituents both A site and B site, offering more possiblities of vacancy oxygen which can be greatly improved by doping modification[12, 13]
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