Microwave Intercalation Synthesis of WO₃ Nanoplates and Their NO-Sensing Properties

Tungsten(VI) oxide (WO₃) nanoplates were successfully synthesized by microwave intercalation. Through microwave processing, an intermediate product H₂W₂O₇·xH₂O was prepared quickly to greatly decrease the time used to prepare WO₃ nanoplates. The crystal structure and morphology of WO₃ were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The morphology of WO₃ changed with an increase in calcining temperature. A mixed-potential NO_x sensor using planar yttria-stabilized zirconia and WO₃ as the sensing electrode (SE) was fabricated, and its performance in NO_x detection at high temperature was examined. It was determined that at 500 °C, the sensor with the WO₃-nanoplate SE had higher sensitivity to NO than the sensor with a SE consisting of WO₃ microparticles. The response of the NO sensor with a WO₃-nanoplate SE was linear with the logarithm of NO concentration in the range of 100-1000 ppm. The electrochemical impedance measurements indicate that the electrode reaction that occurred at the triple-phase boundary (TPB) of the sensor with WO₃-nanoplate SE was stronger than the reaction that occurred at the TPB of the sensor with WO₃-microparticle sensing electrode.