Managing H2O Cross‐Sensitivity Using Composite Electrolyte NOx Sensors

Abstract

NO x sensors composed of partially stabilized zirconia (PSZ), fully stabilized zirconia (FSZ), and PSZ-FSZ composite electrolytes were investigated using impedance spectroscopy under dry and humidified gas conditions. The impedance data were used to interpret the electrochemical behavior of the various sensors as the water concentration in the gas stream varied. The sensors were operated in the presence of 0-100 ppm NO with 1-18% O 2 and 3-10% H 2 O with N 2 as the balance gas. The operating temperature of the sensors ranged from 600 to 700 C. The impedance response for sensors containing ≥ 50 vol% PSZ slightly decreased under humidified gas conditions, in comparison to dry gas conditions; whereas, a significant increase in impedance occurred for sensor largely containing FSZ. This indicated water cross-sensitivity was substantial at FSZbased sensors. The microstructural properties, NO x sensitivity, oxygen partial pressure and temperature dependence, as well as the response time of the sensors composed of the various electrolytes were characterized in order to interpret the electrochemical response with respect to water cross-sensitivity. Analysis of the data indicated that sensors composed of a PSZ-FSZ composite electrolyte with 50 vol% PSZ were more suitable for detecting NO x while limiting water cross-sensitivity.

Investigation of an Impedimetric LaSrMnO3-Au/Y2O3-ZrO2-Al2O3 Composite NOx Sensor

“…Such a defect pair may influence the free vacancy concentration and, thus, affect the ionic conductivity of the FSZ composite electrolyte [ 32 ]. As the ionic conductivity of FSZ was about 50% higher than that of PSZ [ 24 ], oxygen ion transport would not be as rapid via the PSZ particles within the FSZ composite electrolyte. Therefore, limited oxygen ion transport at PSZ particles, along with the presence of Al 2 O 3 particles, may restrict electrochemical reactions with interfering gases in the composite electrolyte.…”

“…Increasing the Al 2 O 3 concentration beyond 2 wt% adversely impacted sensor sensitivity to NO as the insulating properties of Al 2 O 3 became apparent [ 23 ]. Related composite electrolyte studies suggested that the presence of PSZ in the sensor electrolyte may be beneficial for reducing water cross-sensitivity, thereby promoting NO x sensor accuracy [ 24 ].…”

“…The composite NO x sensors included a porous composite electrolyte composed of fully stabilized and partially stabilized ZrO 2 (i.e., FSZ and PSZ) along with Al 2 O 3 . The authors selected these materials, as prior studies suggested that composite electrolytes contributed to greater NO x sensing capabilities, along with reduced water cross-sensitivity [ 22 , 24 ]. To the authors’ knowledge, other studies have not evaluated the behavior of NO x sensors entirely composed of composite materials.…”

Development of an Activity-based Windowing Approach to Evaluate Real-World NOx Emissions from Modern Medium and Heavy-Duty Diesel Trucks

“…Substantial developments in stringent emissions regulations and advancements in MD and HD diesel engine/aftertreatment technology are the primary driving force for improvements in accuracy and sensitivity/selectivity of NOx sensor technology. (Frobert et al, 2013;Murray et al, 2017;Sakai et al, 2003;Soltis et al, 2006;Todo et al, 2018). Therefore, to be implemented as a feasible, cost-effective alternative for NOx monitoring, it is essential to gain an in-depth understanding of the impact of cross-sensitivity on sensor-based measurements.…”

“…Therefore, to be implemented as a feasible, cost-effective alternative for NOx monitoring, it is essential to gain an in-depth understanding of the impact of cross-sensitivity on sensor-based measurements. (Moos, 2005;Murray et al, 2017). The sensor includes a heater that is used to keep the sensor element at high temperatures (i.e., above 600 °C) to collect measurements with high resolution.…”