Development of Potentiometric Sensors for C₂H₄ Detection.

Gas exhaust emissions in vehicles are increasingly restrictive in EU and USA. Diesel engines are particularly affected by limitation in hydrocarbons and NOx concentrations. This work presents a screening of working electrode materials to develop a potentiometric sensor, with the most promising material to detect being C₂H₄ at 550 °C. The device consists of a dense 8YSZ (8 mol% Y₂O₃ stabilized ZrO₂) disk as oxide-ion conducting electrolyte, whereas platinum is screen-printed in the back face as reference electrode. As working electrode, several materials such as Fe0.7Cr1.3O₃, ZnCr₂O₄, Fe₂NiO₄, La0.8Sr0.2CrO3-δ (LSC), La0.8Sr0.2MnO₃ (LSM), and NiO+5%wt Au were tested to detect C₂H₄. Sensor voltage was measured for several concentrations of C₂H₄ and CO as these are two of the major oxidizable compounds in a diesel exhaust gas. Fe0.7Cr1.3O₃ was selected as the most promising material because of its response to C₂H₄ and CO. Not only is the response to the individual analytes important, but the C₂H₄ cross-sensitivity toward CO is also important. Fe0.7Cr1.3O₃ showed a good performance to C₂H₄, with low cross-sensitivity to CO. In addition, when 0.16 ppm of phenanthrene is added, the sensor still has a slightly better response to C₂H₄ than to CO. Nevertheless, the sensor exposure to high concentrations (>85 ppm) of polycyclic aromatic hydrocarbons led to signal saturation. On the other hand, the operation in wet conditions induces lower sensor sensitivity to C₂H₄ and higher cross-sensitivity toward CO increase, i.e., the sensor response becomes similar for C₂H₄ and CO.