Electrochemical NOx Sensors for Emission Control of Automotive Exhaust Gas

Electrochemical NO_x sensors for emission control of automotive exhaust gas were prepared coupling pellets of yttria-stabilized zirconia (YSZ), an oxygen ion conductor, with thick films of a semiconducting oxide (WO₃) as an auxiliary phase. The obtained sensors were wholly exposed to the same atmosphere. Electromotive force (EMF), polarization curves and amperometric measurements were performed in air and at different concentrations of NO₂ in air, at selected temperatures. Stable EMF values and fast response times were obtained. The sensors showed non-linear polarization curves. The role played by the electrolyte/electrode interface was determined by electrochemical impedance spectroscopy (EIS) tests: exposure to NO₂ did not affect the bulk but only the electrolyte/electrode interface.