Electrically Biased NOx Sensing Elements with Coplanar Electrodes

Fabrication and characterization of electrically biased NOx sensing elements operative at 500-600DGC are described. The sensing elements were produced by screen-printing Pt and transition metal oxide electrodes on yttria-stabilized zirconia substrates. DC electrical biasing greatly enhanced the response of the sensing elements to nitric oxide (NO)x with voltage changes on the order of 10% observed as the sensing response to 450 ppmv NO at 600.DGC and 7 vol % O2. Voltage and current biasing techniques were employed with a sensing element using NiCr2O4 as the oxide, and the computed changes in resistance due to NO were nearly identical, suggesting that the response mechanism of the elements is a change in dc electrical resistance. The sensing response was minimally affected by O2 concentrations between 7 and 20 vol % at [NO] concentration levels from 0 to 1500 ppmv. These sensing elements and techniques may be useful in sensors for measuring [NO] at temperatures near 600DGC.