Sri Ayu Anggraini

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.

Insight into the Aging Effect on Enhancement of Hydrogen-Sensing Characteristics of a Zirconia-Based Sensor Utilizing a Zn–Ta–O-Based Sensing Electrode

A significant enhancement in the hydrogen (H2) sensitivity as well as selectivity after aging for more than 40 days has been observed for a mixed-potential-type sensor using ZnO (+84 wt % Ta2O5) as the sensing electrode (SE) and yttria-stabilized zirconia (YSZ) as the solid electrolyte. The effect of the aging process in enhancing the sensing characteristics of the sensor using ZnO (+84 wt % Ta2O5)-SE was studied here by investigating the changes in the morphology, crystal structure, chemical surface state, and catalytic properties of the SE material before and after aging at 500 °C for 80 days. X-ray diffraction measurements confirmed that the crystal structure of the SE material was found to be unaffected by aging, while the morphological change observed via scanning electron microscopy imaging indicated a decrease in the porosity and an increase in the particle size after aging. A significant change, particularly in the binding energy of Ta 4f, was also observed for the SE material after long-term aging. Although the catalytic activities toward the anodic reaction of H2 and the other examined gases were moderately stable after aging, a significant decrease in the heterogeneous catalytic activity of the gas-phase reaction (oxidation) of H2 was observed. Such a trend presumably resulted in a higher fraction of H2 reaching the triple-phase boundary, where the electrochemical reactions generate a sensing signal (mixed potential), resulting in high H2 sensitivity as well as high H2 selectivity after long-term aging of the present sensor.

6.5.1 Sensitive and Selective Detection of Hydrogen Using YSZ-based Sensor with Zn-Ta-based Oxide Sensing-electrode

An yttria-stabilized zirconia (YSZ)-based sensor utilizing a Zn-Ta-based oxide sensing electrode (SE) is reported herein as being capable of generating sensitive and selective response toward hydrogen (H2). The addition of 84 wt.% Ta2O5 into ZnO brought about the highest response toward H2, when compared with other examined Zn-Ta-based oxide SE materials. After a stabilization period of about 50 days, the sensor exhibited a stable and high sensitivity (Δemf) of approximately -600 mV toward 100 ppm H2 and low cross-sensitivity towards other examined gases (< ± 80 mV) at 500 o C under humid operating conditions (20 vol.% O2 and 5 vol.% H2O). An almost linear relationship between sensitivity and H2 concentration (10-100 ppm) was observed for the developed sensor.