Amperometric NOx Sensor Based on Oxygen Reduction

A novel ceria-based amperometric NO
_x
and NH
₃
sensor was investigated. The sensor consisted of gadolinium-doped ceria electrolyte membrane with (La
_0.60
Sr
_0.40
) (Co
_0.20
Fe
_0.80
)O
_3-δ
(LSCF) electrodes applied to opposite sides. The assembly operated in combustion exhaust streams with higher sensitivity to both NO
_x
and NH
₃
, less dependence on oxygen partial pressure, and faster response than previously reported. The sensor had an operational temperature range of 200 °C-550 °C and was resistant to common exhaust gas contaminants, such as steam, CO
₂
, and sulfur oxides. Electrochemical testing and in-situ DRIFTS studies showed NOx adsorption on the sensor causing accelerated kinetics for oxygen reduction reaction (ORR) whereby adsorbed NOx species acted as a catalyst for an alternative ORR pathway, thus enabling an amperometric sensing mechanism.