Zirconia-based mixed potential sensors using precursor Bi 2 W 2 O 9 and tungsten nanoplate sensing electrode for detection of NO 2

Sensing electrodes with two different materials (precursor Bi 2 W 2 O 9 and the tungsten oxide) were synthesized. The tungsten oxide with high specific surface area (78 m 2 g −1 ) was prepared by acid leaching of Bi 2 W 2 O 9 under microwave processing and the ultrasonic exfoliation reaction. The structure and morphology of the precursor Bi 2 W 2 O 9 and the tungsten oxide were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and the Brunauer–Emmett–Teller method. The mixed potential NO 2 sensors based on yttria-stabilized zirconia and sensing electrodes with the two materials were fabricated and compared and then their sensing properties were examined. All sensors showed good response to 30–500 ppm NO 2 at their best operation temperature. The sensor equipped with exfoliated tungsten oxide exhibited the better sensing performance than the sensor equipped with precursor Bi 2 W 2 O 9 , which shows the sensitivity of 64.61 mV decade −1 to NO 2 at the minimum operation temperature of 450 °C. In addition, the stability, repeatability, and cross-sensitivity of the two sensors were analyzed in details. Furthermore, the mixed potential sensing mechanism of NO 2 for the tungsten oxide was also discussed.