Electrochemical Characterization of Electrode Materials for Mixed-Potential Sensors

The Sensors and Electrochemical Devices group at LANL along with Electro-Science Laboratories (ESL) have developed a reproducible mixed potential NO_x sensor for application in automotive emission control systems. The pre-commercial sensor has a perovskite working electrode (La_1-xSr_xCrO₃) and a platinum counter electrode, and an Yttrium Stabilized Zirconium (YSZ) electrolyte layer on one side; with a resistive platinum heater on the other side. While the planar sensor that was developed has been extensively studied, several fundamental questions still need to be answered. This study will attempt to answer the question as to how the performance of the sensor changes as the composition of the working electrode is varied. This study uses a button cell in place of the stick sensor. This cell is constructed using the same materials and processes that formed the stick sensors except that it uses a dense YSZ disk with the electrodes on printed on opposite sides. The rationale for using the button cell is so that there is a reference electrode, in this case the platinum electrode, exposed to a controlled reference gas. In this study, we will investigate the change in the sensitivity and selectivity when the Strontium content of the perovskite electrode is changed. The changes will be characterized by using various electrochemical techniques. Information obtained from characterizing varying electrode materials in the button cell configuration will provide insight for tuning selectivity and sensitivity of future planar mixed-potential sensors.