Compact electrochemical bifunctional NOx/O2 sensor with metal/metal oxide internal reference electrode for high temperature applications

Simultaneous measurement of total NOx and O2 using two electrochemical methods are demonstrated using metal/metal oxide internal oxygen reference electrode-based sensors at high temperatures. The Pd/PdO-containing reference chamber was sealed within a stabilized zirconia superstructure by a high pressure/temperature plastic deformation bonding method exploiting grain boundary sliding between the ceramic components. Amperometric and potentiometric NOx sensing devices were assembled on the outside of the sensor. Pt-loaded zeolite Y was used to obtain total NOx capability. Both the amperometric and potentiometric type sensors showed total NOx response, with the potentiometric device showing better NOx/O2 signal stability and lower NOx–O2 cross-interference. Since these sensors do not require plumbing for reference air, there is more flexibility in the placement of such sensors in a combustion stream.