Mixed-potential-type NOx sensor based on YSZ and zinc oxide sensing electrode

Abstract

Abstract. 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 ~ The response of the ZnOattached 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.

Electrochemical NOx sensors based on stabilized zirconia: comparison of sensing performances of mixed-potential-type and impedancemetric NOx sensors

“…Figure 4 depicts the dependence of emf (NOx sensitivity) on logarithm of NOx concentration for all the thicknesses of ZnCr 2 O 4 -SE at 700 • C. Here, the NOx sensitivity is defined as: emf = emf Nox -emf air . It is noted that the sensitivity to NO is opposite to and much lower than that to NO 2, as reported previously [2][3][4][5][6][7][8][9][10][11][12]. It is seen that in each case the | emf | value increases almost linearly with increasing NOx concentration on a logarithmic scale.…”

“…Based on our previous experience, the sensing mechanism of the potentiometric YSZ-based sensor can be explained by mixed-potential model as reported elsewhere [6,[8][9][10][11][12]. The non-electrochemical gas-phase reaction (2) occurring in the SE matrix also plays an important role in deciding the NOx sensitivity of the sensor [9,12,14].…”

“…Table 1 summarizes various types of oxide-SEs and their NOx sensing characteristics for the mixed-potential-type sensors reported by us over a decade. We have extensively investigated several oxide-SEs, such as CdMn 2 O 4 [2,3], CdCr 2 O 4 [4,5], WO 3 [6,7], NiCr 2 O 4 [8], ZnFe 2 O 4 [9,10], ZnCr 2 O 4 [11], ZnO [12]. For the first time in this sensor field, we have currently reported that NiO can detect NO 2 even at high temperature of 900 • C under wet condition [13,14].…”

“…The advantages of the sensor are fast response, portability, low cost and operation at elevated temperatures in a harsh environment. Significant progress has been made towards the development of mixed-potential-type NOx sensors based on YSZ and catalytically active metal-oxide SE [2][3][4][5][6][7][8][9][10][11][12]. Table 1 summarizes various types of oxide-SEs and their NOx sensing characteristics for the mixed-potential-type sensors reported by us over a decade.…”

“…Apart from the mixed-potential-type NOx sensors, we have proposed and examined quite recently a new-type impedancemetric NOx sensor based on YSZ and ZnCr 2 O 4 -SE [25,26]. For the mixed-potential type sensors, it is known that the sensitivity to NO 2 is much higher than that to NO and in addition the sensitivity to NO 2 is opposite to that to NO [2][3][4][5][6][7][8][9][10][11][12]. In contrast, this tendency is completely different for the impedancemetric sensor, as has been reported elsewhere [25,26]: the complex-impedance value at rather low frequency decreases with an increase in concentration of both NO and NO 2 .…”