Mitsunobu Nakatou

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.

NO x Sensing Characteristics of Mixed-Potential-Type Zirconia Sensor Using NiO Sensing Electrode at High Temperatures

A stabilized-zirconia-based NO x sensor attached with oxide sensing-electrode (SE) was tested for the detection of NO x at temperatures higher than 800°C for car-emission control applications. Among various oxide SEs tested, NiO was found to give the highest sensitivity to NO 2 even at high temperatures. It was found that the sensor using NiO-SE showed quicker recovery in the presence of water vapor, compared with that in the dry sample gas. Electromotive force values of 57 and 75 mV were observed, respectively, under dry and wet (5 vol % water vapor) conditions with 400 ppm NO 2 at 850°C.

Impedancemetric zirconia-based sensor for detection of propene at high temperature

We report here that impedancemetric sensor based on yttria-stabilized zirconia (YSZ) can detect propene (C/sub 3/H/sub 6/) sensitively and selectively under wet condition, if the selection of sensing-electrode (SE) material and operating condition is made properly. Among the various single-oxide SEs examined, ZnO was found to give rather high sensitivity to C/sub 3/H/sub 6/ at 600/spl deg/C in the presence of 1 vol.% H/sub 2/O as well as negligible sensitivity to CH4 which is not regulated as an air pollutant. In addition, when 1.5 wt.% Pt was loaded on ZnO-SE and the potential of +50 mV vs. Pt counter-electrode (CE) was applied to this SE, the present sensor was found to detect C/sub 3/H/sub 6/ rather sensitively with little interference of other gases, such as CO, NO, NO/sub 2/, H/sub 2/, CH/sub 4/, CO/sub 2/, H/sub 2/O and O/sub 2/, at 600/spl deg/C.