A novel mixed potential NH3 sensor based on TiO2@WO3 core–shell composite sensing electrode

The TiO2@WO3 core-shell composite with mass ratio of core and shell4:1 was prepared by a hydrothermal synthesis method using sodium tungstate dehydrate, nitric acid and commercial TiO2 powder as raw materials. A novel mixed potential NH3 sensor was fabricated by using above-mentioned TiO2@WO3 as sensing electrode and La10Si5.5Al0.5O27 as solid electrolyte. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and structure of the samples. The sensor response to NH3 was examined at 400∼550 °C. The experimental results indicated that the sensor based on TiO2@WO3 sensing electrode possessed greatly enhanced NH3 sensing properties including higher and more stable response value and faster response rate compared to the sensor using TiO2, WO3 or TiO2-WO3 mixture sensing electrode under the same conditions. The responding potential values of the sensor with TiO2@WO3 sensing electrode exhibited a linear dependence on the logarithm of the NH3 concentrations. The highest NH3 sensitivity of 74.8 mV/decade was achieved at 450 °C. In the meantime, the sensors also showed well anti-interference capability to CH4, CO2 and H2, but noticeable cross sensitivity toward NO2 was observed. O2 effect on responding signal could be calibrated by predetermining O2 content.