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This paper deals with an impedancemetric sensor based on an yttria-stabilized zirconia (YSZ) using an oxide sensing-electrode (SE) for measuring O 2 concentration. Fourteen oxides were examined as the SE materials for selective detection of O 2 . Among the sensors examined, the YSZ-based sensor using BaFeO 3 -SE was found to be insensitive to interfering gases such as NH 3 , H 2 , C 3 H 6 , C 3 H 8 , CH 4 , NO 2 , NO or CO, while sensitive to only O 2 at 600 °C. The impedance value |Z| at 10 Hz for the sensor using BaFeO 3 -SE decreased linearly with increasing O 2 concentration on a logarithmic scale in the range of 0.05–21 vol.%. The present sensor exhibited quick and repeatable responses to the change in O 2 concentration. [ABSTRACT FROM AUTHOR]

Perovskite-type oxides of Ba x Sr 1 - x FeO 3 (x = 0, 0.1, 0.5, 0.9 and 1.0) were examined as a sensing electrode (SE) material of potentiometric yttria-stabilized zirconia (YSZ)-based oxygen sensors. The sensors using each of Ba x Sr 1 - x FeO 3 -SEs were found to be insensitive to the various examined gases (100 ppm each) such as NH 3 , H 2 , C 3 H 6 , C 3 H 8 , CH 4 , NO 2 , NO and CO, while they were sensitive to oxygen in the concentration range of 0.05-21 vol.% at 600 °C. The number of electron (n) in the electrochemical reaction of oxygen for the present sensors was estimated to be about 4.2 based on Nernst equation in the examined concentration range. The estimated n values for the present sensors are consistent with that (n = 4.2) for the conventional YSZ-based oxygen sensor using Pt-SE, being almost same as the theoretical value (n = 4). The YSZ-based sensor attached with BaFeO 3 -SE further showed excellent responses at temperatures of 450–600 °C. The electric potential difference (Δ V ) value of the present sensor was rather stable under the operating conditions (relative humidity: 20–100%, 400 ppm CO 2 , 600 °C) for the examined period of 14 days. In addition, it was found that the sensor using BaFeO 3 -SE could work well as a lambda (λ) sensor at 600 °C in the combustion gas of O 2 /C 3 H 8 , as is the case with the sensor using Pt-SE. [ABSTRACT FROM AUTHOR]

An yttria-stabilized zirconia (YSZ)-based sensor using Zn–Ta-based oxide as a sensing electrode (SE) has been previously reported to generate a highly sensitive and selective response to hydrogen (H 2 ) after the aging of 40 days at 500 °C. This study is focused on shortening such a long aging time (stabilization) for obtaining the high-performance of the sensor. Initially, different heat treatments (changing the sintering parameter and the aging temperature) were done and could not give satisfactory results. However, when the sensor was exposed to 400 ppm H 2 in N 2 (the H 2 treatment), the stabilization time was found to decrease from 40 to 24 days. Prolongation of the H 2 -treatment time from 30 to 60 min helped the sensor using Zn–Ta–O-SE to reach the stabilized level in 15 days. Extending the treatment time up to 120 min gave an adverse effect to the shortening of stabilization time. Furthermore, the sensing performance of the stabilized sensor received the 400 ppm H 2 treatment for 60 min was unaffected by this H 2 treatment, since the sensor was still able to exhibit likewise highly sensitive and selective response to H 2 after the stabilized state was achieved. [ABSTRACT FROM AUTHOR]

We are reporting here a potentiometric sensor by using yttria-stabilized zirconia (YSZ) as a solid electrolyte as well as zirconium silicate (ZrSiO 4 ) added with Au as a sensing electrode (SE), for achieving sensitive and selective detection of hydrogen (H 2 ). The addition of 10 wt.% Au into ZrSiO 4 -SE increased the sensitivity toward 100 ppm H 2 at 500 °C, while lower responses to other examined gases were observed. The ability to detect H 2 selectively was elucidated via polarization-curve measurements in air and in N 2 and confirmed via gas conversion test. It was found that the sensitive and selective H 2 behavior was due to a lower catalytic activity against the gas-phase oxidation of H 2 than that of C 3 H 6 , in combination with a higher catalytic activity to anodic reaction of H 2 than that of C 3 H 6 . The good agreement between the observed sensitivity and the estimated value from the polarization-curve measurements confirmed that the sensing mechanism is based on mixed potential model. The sensor using ZrSiO 4 (+ 10 wt.% Au)-SE demonstrated a linear relationship between sensitivity and H 2 concentration on a logarithmic scale and was capable of detecting H 2 concentration as low as 20 ppm at 500 °C under humid conditions. [ABSTRACT FROM AUTHOR]

Various metal oxides were examined for a sensing-electrode (SE) material of potentiometric yttria-stabilized zirconia (YSZ)-based oxygen sensors. Among the oxides tested, perovskite-type oxides of Ba x Sr 1 − x FeO 3 (x = 1.0, 0.9, 0.5, 0.1, 0) were found to give low responses to various gases (NH 3 , H 2 , C 3 H 6 , C 3 H 8 , CH 4 , NO 2 , NO, and CO, 100 ppm each) at 600 °C. Particularly, BaFeO 3 -SE gave the most insensitive behavior to all the gases tested even in the temperature range of 500–600 °C, as the conventional Pt-SE did. Furthermore, the sensor using this inexpensive BaFeO 3 -SE was found to be quite sensitive to oxygen in the concentration range of 0.05–21 vol.% at temperatures of 500–600 °C, as similar to the case of an expensive Pt-SE. At 600 °C, the number of electron (n) involved in the electrochemical reaction of oxygen for the sensors using each of BaFeO 3 -SE and Pt-SE was estimated to be 4.2, which was obtained from the slope of linear correlation between potential response and the logarithm of oxygen concentration. The estimated n value was in good agreement with the theoretical value (n = 4). The present sensor using BaFeO 3 -SE was also confirmed to work well as a λ (lambda) sensor at 600 °C, showing similar behavior as the sensor using Pt-SE did. [ABSTRACT FROM AUTHOR]

A selective carbon monoxide (CO) sensor was developed by the use of both of CuCrFeO 4 and CoCrFeO 4 as the sensing electrode (SE) for yttria-stabilized zirconia (YSZ)-based potentiometric sensor. The sensing-characteristic examinations of the YSZ-based sensors using each of spinel oxides as the single-SE sensor showed that CuCrFeO 4 -SE had the ability to detect CO, hydrocarbons and NO x gases, while CoCrFeO 4 -SE was sensitive to hydrocarbons and NO x gases. Thus, when both SEs were paired as a combined-SEs sensor, the resulting sensor could generate a selective response to CO at 450 °C under humid conditions. The sensor was also capable of detecting CO in the concentration range of 20–700 ppm. Its sensing mechanism that was examined via polarization-curve measurements was confirmed to be based on mixed-potential model. The CO response generated by the combined-SEs sensor was unaffected by the change of water vapor concentration in the range of 1.3–11.5 vol% H 2 O. Additionally, the sensing performance was stable during 13 days tested. [ABSTRACT FROM AUTHOR]