Development of Planar Potentiometric Gas Sensors for Automotive Exhaust Application

Abstract

In the past, we have deeply investigated the development of a b-alumina potentiometric sensor with two coplanar metallic electrodes. Recently, many papers have demonstrated an interest for similar non-Nernstian devices based on stabilised zirconia (YSZ) electrolyte. The common particularity of such sensors is related to the use a dissymmetry of electrodes on an electrolyte and to work in a single gas cell. Our main experimental results obtained with b-alumina sensors are reported with the special attention to develop gas sensors for exhaust applications. The sensors are evaluated under CO, HC and NO x CO. The selectivity depends on the sensor temperatures. The performances appear sufficient to satisfy in the future automotive applications like the control of NOxTrap or DeNOx devices. The measure of NH 3 concentrations seems also possible. The comparison of performances of sensors replacing b-alumina electrolyte by YSZ is also presented. Similar behaviours are obtained for both types of sensors. These comparisons reinforce our proposal of a capacitive model mainly based on the difference of reactivity of the electrodes. It is pointed out that mixed potentials cannot explain the behaviour of our sensors under oxygen. Very good agreements are obtained between this capacitive model and the experimental results, not only versus oxygen, but also with mixture of oxygen and CO.

Half-Cell Potential Analysis of an Ammonia Sensor with the Electrochemical Cell Au | YSZ | Au, V2O5-WO3-TiO2

“…According to mixed potential theory, two electrochemical reactions compete at the TPB and form a mixed electrode potential [22,23,31,32]. A mixed potential establishes if the reaction rates of the anodic and the cathodic electrochemical reaction are equal, i.e.…”

“…The reaction rates of the electrochemical reactions, catalytic properties of the electrodes, and adsorption properties of the electrodes are not included [10,27,34–36]. More comprehensive approaches for theoretical description of the mixed potential can be found in References [10,27,32,34]. The classic mixed potential theory [10,22,34] bases on the Butler-Volmer equation, which can be investigated with I - V -curves.…”