Impedancemetric NO[sub x] Sensing Using YSZ Electrolyte and YSZ∕Cr[sub 2]O[sub 3] Composite Electrodes

Abstract

An impedancemetric method for sensing using an yttria-stabilized zirconia (YSZ)-based electrochemical cell is described. The sensor cell consists of a planar YSZ electrolyte and two identical composite electrodes exposed to the test gas. The sensor response to a sinusoidal ac signal applied between the two electrodes is measured via two parameters calculated from the complex impedance, the modulus and phase angle Θ. While either of these parameters can be correlated to the concentration in the test gas, Θ was found to provide a more robust metric than . At frequencies below approximately , Θ is sensitive to both the and concentrations. At higher frequencies, Θ is predominantly affected by the concentration. A dual frequency measurement is demonstrated to compensate for changes in the background between 2 and 18.9%. Excellent sensor performance is obtained for concentrations in the range of in background. An equivalent-circuit model was used to extract fitting parameters from the impedance spectra for a preliminary analysis of -sensing mechanisms.