Non-Nernstian planar YSZ-based electrochemical sensors using semiconducting oxide electrodes

New gas sensing devices based on solid state electrochemistry with a planar geometry are presented. The complete devices combine an improved processing technology of yttria-stabilized zirconia (YSZ) foils with platinum and semiconducting oxide electrodes. The microstructural and catalytic properties of the electrodes defined the sensing response, which exhibited a nonNernstian electrochemical nature, as expected. Sensors with WO ₃-based electrodes showed the best sensitivity to NO _x among other options, with the highest selectivities in respect to CO at the lowest temperatures. In the case of Al ₂O ₃:Pt sensing electrodes, a differential gas diffusion principle of operation was considered, detecting CO without much selectivity to NO _x.