Nitrogen Monoxide Gas Sensor with Nitrosonium Ion (NOィイD1+ィエD1) Conducting Solid Electrolytes

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Nitrogen oxides are one of predominant pollutant gas species in the world wide scale. In particular, nitrogen monoxide (NO) is a main pollutant. The suppression of the NO exhaustion has been becoming an urgent issue. An accurate NO sensing method is important for the control of the exhaust amount into the atmosphere. Up to now, various types of compact and inexpensive sensors like semiconducting, solid electrolyte, and organic compound types, have been proposed. Sensing with a semiconductor type has the advantage of detecting gas content by the simple principle of conductivity measurements, but the sensing characteristics are not quantitative or selective.In contrast, the NO detection with a solid electrolyte is specific to only one ion. If the content of the ionic species is directly related to the migrating ion in the solid electrolyte, the solid electrolyte sensor is expected to possess a high selectivity. Furthermore, the sensor output with the solid electrolyte sensor directly fol … More lows the Nernst theoretical relation and a quantitative gas detection can be successfully realized. Because nitrogen monoxide (NO) to be detected, the most suitable ionic species of nitrogen monoxide gas detection is nitrosonium ion (NOィイD1+ィエD1). Therefore, the best solid electrolyte candidate for nitrogen monoxide sensing is the NOィイD1+ィエD1 conducting solid electrolyte.In this research, a nitrosonium (NOィイD1+ィエD1) ion conducting gallate solid electrolyte is applied since the ionic conductivity of NaィイD1+ィエD1-β-GaィイD22ィエD2OィイD23ィエD2 is higher than that of NaィイD1+ィエD1-β-AlィイD22ィエD2OィイD23ィエD2. The NO sensing characteristics of the compact NO sensor with the NOィイD1+ィエD1 ion conductor was clearly demonstrated.The NO gas content was changed from 50 to 250 ppm which is one of typical of NO content in the emitted gas such as from boiler. The response was reasonably reproducible and the time necessary for obtaining 90% response was about 1.5 min. The output of the sensor was directly proportional to the logarithm of the NO gas pressure. The sensor output obtained as an electromotive force increased with an increase in the NO gas content. The slope of the line was 1.06, in excellent accordance with that calculated from the Nernst theoretical equation.In conclusion, the compact NO sensor composed of NOィイD1+ィエD1 ion conductor of NOィイD1+ィエD1-GaィイD211ィエD2OィイD217ィエD2 and NaNOィイD22ィエD2 as the reference electrode was found to theoretically respond to the NO gas concentration. The detection was accurate, quantitative, rapid, and also reproducible. Less