Mixed-potential type NH3 sensor based on CoWO4-PdO sensing electrode prepared by self-demixing

CoWO 4 -PdO dual phase composites were successfully prepared by self-demixing of the precursor CoPd x WO 4+x (x = 0, 2%, 5%, 10%) calcined at 800 °C and used as sensing electrodes for mixed-potential type NH 3 sensors based on yttria stabilized-zirconia (YSZ) electrolyte. The materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Field-emission scanning electron microscopy (FESEM), respectively. NH 3 response performance of the sensors to different concentrations of NH 3 (20–300 ppm) was evaluated at 350–500 °C. It was found that the sensors attached with CoWO 4 -PdO sensing electrode are much more sensitive to NH 3 than the CoWO 4 -based sensor. Among them, CoWO 4 -5%PdO based sensor gives the highest sensitivity (−76.8 mV/decade at 400 °C), the response signals (Δ V ) of the sensor vary linearly with the logarithm of the NH 3 concentrations in the range of 50–300 ppm at a given temperature. The sensor also exhibits well reproducibility, stability and long-term stability. Furthermore, compared with CoWO 4 -based sensor, the introduction of PdO in CoWO 4 makes the interference of NO 2 on the sensor significantly reduced from 100% to 50%, which is attributed to the fact that the second phase PdO depresses the adsorption of NO 2 .