Planar impedancemetric NO sensor with thick film mixed dy-based oxides sensing electrodes

The pastes destined for sensing electrodes were prepared by mixing Dy-based oxides powders with organic vehicle. The sensing electrodes of interdigitated structure were screen printed onto yttria stabilized zirconia substrates, fabricated from commercially available solid electrolyte green tape. The fabricated sensor was placed in a vertical type gas flow apparatus equipped with heating elements. Impedance spectroscopy was performed upon exposing the sensor to gas mixtures containing NO gas in the concentration range from 0 to 400 ppm, while temperature and gas flow rate were kept constant throughout the measurements. For frequencies spanning from 30 mHz to 100 kHz, the impedance response of the fabricated sensor to the NO gas presence was investigated at temperatures in the range from 600 to 750 °C. The study confirmed that the sensor fabricated in thick film technology is sensitive to nitric oxide in the concentration range of measurements, 0-400 ppm, and when phase angle is chosen for a sensing parameter, linear dependency is observed at certain frequencies. The frequencies, at which maximum sensitivity is observed, as well as NO sensitivity values, are found to be dependent on the operating temperature. Impedance arcs found on Nyquist plots were fitted to an equivalent circuit and values of corresponding parameters were determined.