PERFORMANCE OF PROTECTED OXYGEN SENSORS .2. SHORT-CIRCUITED ELECTROCHEMICAL FILTERS

This work reports on the performance of YSZ oxygen sensors protected b y ''electrochemical filters'' based on ionic conductors under external short circuit, or composite materials including one ionic and one ele ctronic conductor. In both cases it is assumed that the electronic con ductor will provide the pathway for electrons or electron holes while the ionic conductor provides the pathway for oxygen ions. These soluti ons were envisaged to overcome the limited performance of single phase mixed conducting filters which exhibit relatively low electrochemical permeabilities. A simplified model has been derived to relate the ste ady state and transient behavior of these devices to the most relevant system and materials parameters determining the sensor performance. T heoretical predictions are compared with experimental data obtained wi th different types of materials combinations and qualitative agreement is found between predicted and effective role of different parameters on protected sensor performance. In these concepts the sensor transie nt response depends strongly on the ionic resistance of the filter, al though for high temperatures this will become negligible and identical to the electronic component.