The Development of Gas Sensors Based on Multivalent Cation Conducting Solid Electrolyte

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Nitrogen oxides are toxic gas species which cause air pollution, and the suppression of Nox gas emission into ambient atmosphere is an urgent issue. For an effective suppression, the on-site sensing of Nox gas at every emitting site is necessary and the development of a practical smart Nox gas sensor with a small size, a high sensitivity and a high selectivity is greatly important. In this research, we newly developed a Nox gas sensor based on trivalent Al^<3+> conducting solid electrolyte and O^<2-> anion conducting yttria stabilized zirconia (YSZ) with a water insoluble auxiliary electrode of the KNO_2 doped Gd_2O_3 solid solution.The present Nox gas sensor shows a high sensing performance according to the theoretical Nemst relationship for the NO detection at 450℃ and its response time for Nox gas concentration variation was within 15 min. On the other hand, the sensor can also respond to the NO_2 gas theoretically similar to the case for the NO gas detection. Furthermore, since the sensor outputs for total Nox gas (NO + NO_2) concentration of 2000 ppm were constant even if the ratio of NO amount in mixed gas changed, the present Nox gas sensor was found to be able to detect the total Nox gas concentration in the ambient atmosphere.In conclusion, the present sensor based on both divalent Al^<3+> and divalent O^<2-> conducting solid electrolytes with water insoluble auxiliary electrode of the KNO_2 doped Gd_2O_3 solid solution was found to be a smart NOx gas sensor which can detect not only individual nitrogen oxides of NO and NO_2 but also total NOx gas. Since the sensor also possesses both the high thermal and chemical stabilities even at elevated temperatures, the practical application of the present NOx gas sensor is greatly expected at every NOx gas emitting site.