Impedancemetric NO sensor based on YSZ/perovskite neodymium cobaltite operating at high temperatures

A solid-state planar impedancemetric NO sensor was fabricated using yttria stabilized zirconia (YSZ) for a solid electrolyte substrate and a perovskite-type oxide Nd0.9Sr0.1CoO3 − δ for thick film sensing electrodes. Electrical properties of the fabricated NO sensor were investigated, for temperature and frequency ranges of 590-810 °C and 10−2-105 Hz, respectively. The results of the impedancemetric measurements were fitted to an appropriate equivalent circuit. A large low frequency semicircular arc that was observed in complex impedance spectra (Nyquist plots) was attributed to physical processes and electrochemical reactions occurring at the sensing electrodes, while high frequency arc detectable at lower temperatures was assigned to the solid electrolyte and solid electrolyte-electrode interface. Sensitivity toward NO was investigated by exposing the impedancemetric sensor to a gas atmosphere containing 0-400 ppm NO. It was found that there is a linear correlation between the phase angle (theta) and the NO concentration to which the sensor was exposed. The highest sensitivity of the fabricated sensor toward NO was found at 750 °C and 0.46 Hz. The proposed sensing mechanism was supported by the results of the NO decomposition over NSC experiment.