Abstract
Nickel oxide and chromium-doped nickel oxide (Ni0.95Cr0.03O1−δ ) were prepared by thermal decomposition of nitrates. The obtained NiO and Ni0.95Cr0.03O1−δ samples were utilized as sensing electrodes (SEs) in yttria-stabilized zirconia (YSZ)-based sensors for detection of NO2 at 800 °C under wet condition (5 vol.% H2O). While the mixed-potential-type planar sensor attached with NiO-SE gave rather large NO2 sensitivity, the sensor attached with Ni0.95Cr0.03O1−δ -SE exhibited fast recovery rate with an acceptable sensitivity. The Δemf (electromotive force) of the sensors varied linearly with NO2 concentration in the examined range of 50–400 ppm on a logarithmic scale. Based on the results of measurements for polarization, complex impedance and gas phase catalysis, the fast recovery was attributable to the high rate for the anodic reaction of O2 at the Ni0.95Cr0.03O1−δ /YSZ interface, and the lower NO2 sensitivity was caused by both the high rate for the anodic reaction of O2 and the high degree for the gas phase conversion of NO2 to NO.
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