Compact electrochemical bifunctional NO sub(x)/O sub(2) sensor with metal/metal oxide internal reference electrode for high temperature applications

Simultaneous measurement of total NO sub(x) and O sub(2) 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 NO sub(x) sensing devices were assembled on the outside of the sensor. Pt-loaded zeolite Y was used to obtain total NO sub(x) capability. Both the amperometric and potentiometric type sensors showed total NO sub(x) response, with the potentiometric device showing better NO sub(x)/O sub(2) signal stability and lower NO sub(x)-O sub(2) 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.