Selective Detection Of NO2 Research Articles

Selective detection of NO by using an amperometric sensor based on stabilized zirconia and oxide electrode

Stabilized zirconia-based devices using oxide electrode (CdCr 2O 4) were fabricated and examined for selective amperometric detection of NO at high temperature. The CdCr 2O 4-attached tubular device showed quick and selective response to NO over NO 2 at 500 and 550°C, if the potential of sensing electrode was polarized properly at +100 mV vs the reference Pt electrode. The 90% response time of the device to 100 ppm NO was as short as ≈20 s at 500°C. The current response was well correlated to the NO concentration in the range of 0–200 ppm. Furthermore, the current response was hardly affected by the presence of the other gases, such as NO 2, H 2, CO, CH 4, CO 2, and water vapor. A compact, plate-type device which required no reference gas was also fabricated and its sensing properties were confirmed to be also rather good. A plausible NO sensing mechanism of the present devices was proposed on the basis of the sensing characteristics obtained.

A high temperature amperometric NO sensor based on stabilized zirconia and CdCr2O4 electrode

The emission of nitrogen oxides (NO and NO2 abbreviated as NOx) from automobiles and boilers is one of the main sources of atmospheric pollution. Generally speaking, combustion exhausts, as emitted, usually contain ten times as much NO as NO2, so that, for emission control, the sensitive and selective detection of NO in high-temperature combustion exhausts is more important than that of NO2. Several solid-state sensors to detect NO2 and/or NO have been reported [1±8], but these have problems in applications to emission control. For example, potentiometric or amperometric sensors using NASICON (Na-superionic conductor) and nitrite auxiliary phase [2±5] cannot be operated at temperatures above 250 °C because of the low melting point of the nitrites used (e.g., NaNO2: 271 °C). We recently proposed a new type of potentiometric sensor using a stabilized zirconia and oxide electrode (typically CdCr2O4). The devices are based on a sensing mechanism involving mixed potential at the oxide sensing electrode, and detect NO or NO2 in oxygen containing atmospheres at higher temperature, for example, 500±600 °C [6±8]. Unfortunately, however, one problem is that the sensitivity to NO is far smaller than that to NO2, a problem often encountered with potentiometric devices. A solution was suggested by recent reports that zirconia oxygen pumps may be used for the amperometric detection of NO in oxygen containing atmospheres at high temperature [9±12]. The sensor developed consisted of two serial oxygen pumps, which pumped out gaseous oxygen (®rst) and measured the limiting current due to the electrochemical decomposition of NO (second), respectively. This stimulated us to test the possibility of extending our device containing stabilized zirconia and the CdCr2O4 electrode to an amperometric NO sensor. As a result, this extension has been found to be possible by polarizing the oxide electrode appropriately. The amperometric sensor obtained can detect NO selectively in the presence of oxygen at 500 °C. For this sensor, it is not necessary to pump out the coexisting oxygen beforehand, as described below. 2. Experimental details

Direct electrochemical characterization of superoxide anion production and its reactivity toward nitric oxide in solution

We report in this study, and for the first time the direct and simultaneous electrochemical measurements of both nitric oxide and superoxide anion evolution and reactivity in solution. For this purpose, we have combined the use of two electrodes: a previously developed NO-sensor for the amperometric determination of NO and a carbon microelectrode for the amperometric detection of superoxide anion. The latter electrode displayed a potential use for the selective detection of O2− (generated by the xanthine/xanthine oxidase reaction) with an acceptable selectivity against uric acid. Our electrochemical experiments were validated by the Cytochrome c method and by the use of a different procedure for the generation of the superoxide anions. Our results show that the use of the NO sensor provides the selective detection of NO without any interface of the superoxide enzymatic generator.

Measurement of nitric oxide with an antimonide diode laser

An antimonide diode laser operating near 2.65 mum was used to measure absorption lines of NO gas in the first overtone band. A blended line pair of NO that is sufficiently free of interference from H(2) O to permit the selective detection of NO under reduced pressure conditions was identified. With wavelength-modulation spectroscopy, a rms noise level equivalent to an absorbance of 3.2 x 10(-5) was achieved at a measurement integration time (for a single spectral data point) of 0.1 s. The corresponding detection sensitivity (signal-to-noise ratio of 2) for NO in air at reduced pressure was ~15 ppm m (ppm is parts in 10(6)). Antimonide diode lasers show substantial promise for gas-sensing applications because they can gain access to relatively strong absorption lines of several gases of environmental interest at operating wavelengths at which cryogenic cooling is not required.