The SCR changes the harmful nitrogen oxides by adding the solution AdBlue which reduces environmental pollution and protects the exhaust system.
The YSZ is compacted into a dense ceramic and conducts oxygen ions (O2−) at the high temperatures of a tailpipe such at 400 °C and above.
To get a signal from the sensor a pair of high-temperature electrodes such as noble metals (platinum, gold, or palladium) or other metal oxides are placed onto the surface and an electrical signal such as the change in voltage or current is measured as a function of NOx concentration.
The main challenges in the sensor development are selectivity, sensitivity, stability, reproducibility, response time, limit of detection, and cost.
In addition due to the harsh environment of combustion the high gas flow rate can cool the sensor which alters the signal or it can delaminate the electrodes over time and soot particles can degrade the materials.
High amount of cross sensitivity has been observed in gas sensors due to similarity in electron exchange mechanism between target gases and water molecules.