Serge Zhuiykov

Impedancemetric gas sensor based on zirconia solid electrolyte and oxide sensing electrode for detecting total NOx at high temperature

Abstract A solid-state electrochemical NOx sensor was fabricated by using a closed-one-end yttria-stabilized zirconia (YSZ) tube, an oxide sensing electrode (SE) and a Pt counter electrode (CE). The complex impedance of the device using each of several oxide SEs was measured in the frequency and the temperature ranges of 0.1xa0Hz to 100xa0kHz and 600–700xa0°C, respectively. In most cases, a large semicircular arc was observed in complex impedance spectra (Nyquist plots) in the lower frequency range examined in dry-air flow. Only in the case of the device using ZnCr2O3 SE, the semi-arc shrank to some extent upon exposure to NOx gas. The resistance value (Z′) at the intersection of the semi-arc with the real axis at lower frequencies (around 0.1xa0Hz) varied with concentration of both NO and NO2 in the sample gas. The impedance value at 1xa0Hz of the present device was found to vary almost linearly with the concentration of NO (or NO2) from 50 to 400xa0ppm. The 90% response and 90% recovery times were as short as less than few seconds at 700xa0°C. Furthermore, it is noted that the sensitivity of NO is almost equal to that of NO2. This indicates that the present device can detect the total NOx at higher temperatures.

Mixed potential type sensor using stabilized zirconia and ZnFe2O4 sensing electrode for NOx detection at high temperature

Abstract Electrochemical sensors using tubular yttria-stabilized zirconia (YSZ) and the spinel-type oxide sensing-electrode (SE) were fabricated and examined for NO x detection at high temperatures. For a mixed-potential type NO x sensor, ZnFe 2 O 4 has been found to give the highest NO x sensitivity among the other spinel-type oxides tested and reported to date. The ZnFe 2 O 4 -attached device gave a linear correlation between emf and the logarithm of NO 2 (NO) concentration from 50 to 436xa0ppm in the high temperature range 600–700xa0°C. The sensing mechanism of the sensor has been discussed on the basis of the gas adsorption–desorption behavior and the catalytic activity for the oxides examined.

High-temperature NOx sensors using zirconia solid electrolyte and zinc-family oxide sensing electrode

Abstract Yttria-stabilized zirconia (YSZ) electrochemical sensors attached with the zinc-family oxide (ZnFe 2 O 4 and ZnCr 2 O 4 ) sensing electrode (SE) were fabricated and examined for NOx sensing properties at high temperatures. These oxide-SE-attached devices gave a linear correlation between EMF and the logarithm of NO 2 (or NO) concentration from 50 to 436 ppm in the temperature range 600–700 °C. The sensor using the combination of ZnFe 2 O 4 and ZnCr 2 O 4 was found to give the highest sensitivity to NO 2 in air at 700 °C among the oxide-SEs tested and reported in the literatures to date. Furthermore, addition of Pt to ZnFe 2 O 4 was found to improve the sensing characteristics towards quick response. It was confirmed that the sensing performances to NO 2 were roughly related to those to O 2 for the devices tested here.

A review of mixed-potential type zirconia-based gas sensors

A robust and reliable gas sensing device is considered as a convenient and practical solution for gas concentration monitoring that has become a mandatory requirement in different field of applications. For in situ hazardous gases detection, a mixed-potential type gas sensor has been regarded as a promising solid-state gas sensor. For the past three decades, there has been a significant progress in achieving high performance in mixed-potential type sensors. Therefore, this review is focused on reporting the development of mixed-potential type gas sensors with combined yttria-stabilized zirconia (YSZ) as the base solid electrolyte material and various classes of electrode materials for their potential utilization as a high-performance sensing electrode. The underlying sensing mechanism of a mixed-potential type YSZ-based sensor is elaborated here in detail. Transformation in design and configuration of this type of sensor is also covered in this report. In addition, recent progresses on mixed-potential type gas sensors development for detection of several target gases, such as carbon monoxide, hydrocarbons, nitrogen oxides, hydrogen, and ammonia, are reviewed. Strategies to improve the sensing characteristic, particularly gas sensitivity and selectivity, are also reported. Based on the understanding of the fundamental sensing mechanism and the requirements for high-performance gas sensors, challenges and future trends for this type of gas sensor development are discussed.

Sensing Characteristics of YSZ-Based Mixed-Potential-Type Planar NO x Sensors Using NiO Sensing Electrodes Sintered at Different Temperatures

The correlation between the sintering temperature and the NO 2 sensing performances of the planar mixed-potential-type yttria-stabilized zirconia (YSZ)-based NO x sensor attached with NiO sensing electrode (SE) was studied by materials characterization techniques, such as impedance analysis, polarization analysis, scanning electron microscopy, and transmission electron microscopy. The sensing properties of the planar YSZ-based NO x sensors were investigated in the operating temperature range of 700-900°C. The NO 2 sensitivity of the present sensor was found to be modulated by changing the sintering temperature of NiO-SE. Rather large sensitivity (43 mV) to 100 ppm NO 2 was obtained even at 800°C for the sensor using the NiO-SE sintered at 1400°C. A sensing mechanism that involves mixed potential at SE as well as catalysis in gas-phase reaction was discussed based on the results obtained.

Potentiometric NOx sensor based on stabilized zirconia and NiCr2O4 sensing electrode operating at high temperatures

Abstract The two types of electrochemical sensors using stabilized zirconia and the oxide sensing electrode (SE) were developed for NOx detection at high temperatures. For the mixed-potential-type sensor, NiCr2O4 was found to give fairly excellent NOx sensing characteristics in air among several spinel-type oxides tested. This NOx sensor provided a linear correlation between EMF and the logarithm of NO or NO2 concentration in the range 25–436 ppm and in the temperature range 550–650°C. With fixed bias voltage being applied between the SE (oxide) and the counter (Pt) electrode (CE), the EMF between SE and the reference (Pt) electrode (RE) was measured as a sensing signal. The NiCr2O4-attached tubular device was found to provide selective response to NO over NO2 if SE was polarized at +175 mV versus RE. It was also found that this device gave selective response to NO2 over NO, if SE was polarized at −250 mV versus CE. The new design of the planar device was proposed to avoid the cross-sensitivities to the others gases usually coexisting in car exhausts.

Impedance-based total-NOx sensor using stabilized zirconia and ZnCr2O4 sensing electrode operating at high temperature

Abstract We report here a new-type zirconia-based sensor that can detect total NOx content at high temperatures such as 700 °C. A closed-one-end yttria-stabilized zirconia (YSZ) tube was used as a base sensor material. An oxide sensing electrode (SE) and a Pt counter electrode (CE) were formed on the outer and inner surfaces of the YSZ tube, respectively. The complex impedance of the device using a ZnCr2O4-sensing electrode was measured with an impedance analyzer in the frequency and the temperature ranges 0.1 Hz–100 kHz and 600–700 °C, respectively. A large semicircular arc was observed in complex impedance plots (Cole–Cole plots) in the lower frequency range examined and it seemed to correspond to the electrolyte/electrode interface. The impedance value at 1 Hz of the present device was found to vary almost linearly with the concentration of NO (or NO2) from 50 to 400 ppm in the sample gas at 600–700 °C. Furthermore, it is noted that the sensitivity of NO is almost equal to that of NO2. This means that the present device can detect the total NOx at higher temperatures.

Mixed-Potential-Type NOx Sensor Based on YSZ and Zinc Oxide Sensing Electrode

Electrochemical sensors using tubular yttria-stabilized zirconia (YSZ) and oxide sensing electrode (SE) were fabricated and examined for NOx detection at high temperatures. The mixed-potential-type NOx sensor using ZnO-SE gave the highest sensitivity to NOx among other single-type oxides tested as SEs in the temperature range of 600–700 °C. The response of the ZnO-attached device was a linear for the logarithm of NO2 (NO) concentrations from 40 to 450 ppm. The sensing mechanism of the sensor was discussed on the basis of the gas adsorption-desorption behavior, the catalytic activity data, and electrochemical behavior for oxides examined.

High Temperature NOx Sensor Based on Stabilized Zirconia and ZnFe 2 O 4 Electrode

Electrochemical sensors using tubular yttria-stabilized zirconia (YSZ) and the spinel-type oxide sensing-electrode (SE) were fabricated and examined for NOx detection at high temperatures. The ZnFe2O4-attached device gave a linear correlation between EMF and the logarithm of NO2 (NO) concentration from 50 ppm to 436 ppm in the temperature range 550–700°C. This sensor was found to give the highest sensitivity to NO2 in air among the spinel-type oxides tested and reported to date. The sensing mechanism of the sensor was discussed on the basis of the catalytic activity and the TPD data for the oxides examined.