Electrically biased NO_x sensing elements with coplanar electrodes

Fabrication and characterization of electrically biased NO₂ sensing elements operative at 500-600°C 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), with voltage changes on the order of 10% observed as the sensing response to 450 ppmv NO at 600°C 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 O ₂ 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 600°C.