"Total N Ox " sensing elements with compositionally identical oxide electrodes

N Ox sensing elements consisting of coplanar, compositionally identical oxide electrodes on a yttria-stabilized zirconia substrate are reported. During operation, a dc current (or voltage) is applied to the element, and the resultant voltage (or current) is used as a sensing signal. With the appropriate applied dc current level, these sensing elements can be nearly "total N Ox, " with responses to NO and N O2 of the same algebraic sign and similar magnitude. For example, when an element with La0.85 Sr0.15 Cr1.01 O3 electrodes was operated at 600°C with a fixed dc current of 2.5 μA and fixed [O2] of 7 vol %, 77 ppmV NO and N O2 produced voltage changes of -37 and -40%, respectively. The elements displayed an [O2] sensitivity that was a decreasing function of [N Ox], the dc electrical resistance of the elements varied exponentially with temperature, and the magnitude of the N Ox responses decreased approximately linearly with temperature. Similar N Ox sensing performance was obtained with either constant-current or constant-voltage operation and several different oxides were observed to exhibit qualitatively identical behavior with respect to N Ox sensing and [O2] sensitivity.