Amperometric NO_X sensor based on oxygen pumping current by using LaGaO_3-based solid electrolyte for monitoring exhaust gas

摘要

An amperometric NO sensor using a LaGaO_3 base solid electrolyte was investigated based on the difference of catalytic activity of the electrode. It was found that oxygen pumping current increased upon exposure to NO when Sr_(0.6)La_(0.4)Mn_(0.8)Ni_(0.2)O_3 and La_(0.5)Sr_(0.5)MnO_3 (LSM 55) were used as active and inactive electrodes for NO oxidation, respectively. Effects of electrolyte on the sensitivity were investigated and the sensitivity to NO becomes higher with increasing oxide ion conductivity for electrolyte. By applying LaGaO_3 doped with Ni or Co, the sensitivity of the sensor becomes 1842 μA per decade of NO concentration at 823 K. The oxygen pumping current linearly increased with increasing NO concentration and the sensor responded NO and recovered to the original level within 1 min. The appearance of mixed potential in potentiometric study suggests that oxidation of NO to NO_2 mainly occurs on Sr_(0.6)La_(0.4)Mn_(0.8)Ni_(0.2)O_3 electrode. Although oxygen pumping current of this sensor was slightly affected by change in oxygen partial pressure (P_(O_2), influence by P_(O_2) change is negligibly small. Cross-sensitivity study revealed that NO in exhaust gas can be selectively detected in presence of coexisting gases.