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Abstract: This paper focuses on the gas sensing properties of the mixed-potential-type NO2 sensor based on yttria stabilized zirconia (YSZ) and NiO electrode. The sensing performance of the sensor was improved by modifying the three-phase boundary (TPB). Hydrofluoric acid with different concentrations (10%, 20% and 40%) was used to corrode YSZ substrate to obtain large superficial area of TPB. The scanning electron microscope and atomic force microscopic images showed that the 40% HF could form the largest superficial area at the same corroding time (3h). The sensitivity of the sensor using the YSZ plate corroded with 40% hydrofluoric acid to 20–500ppm NO2 was 76mV/decade at 850°C, which was the largest among the examined HF concentrations. It was also seen that the sensor showed a good selectivity and speedy response kinetics to NO2. On the basis of the measurements of anodic and cathodic polarization curves, as well as the complex impedance of the device, the sensing mechanism was confirmed to involve a mixed potential at the oxide sensing electrode. [Copyright &y& Elsevier]

Abstract: The mixed-potential NOx sensor based on yttria-stabilized zirconia (YSZ) and oxide electrode is considered as a potential device used for the on-board diagnostics. Over the past decades, many researchers have paid their attentions on such YSZ based potentiometric NOx sensors and gotten a lot of achievement in developing new type electrode materials. Recently, in order to enhance the sensing performance of the mixed potential type NOx sensor, we have been focusing on modifying the triple-phase-boundary (TPB) by various techniques, including chemical corroding, the double-tape casting, the pore-forming and laser fabrication method. We also designed and prepared the microstructure of the oxide electrodes by controlling the sintering process for increasing the sensitivity of the NOx sensor. This paper reviews our works with regard to the above-mentioned two aspects. [Copyright &y& Elsevier]

Abstract: A series of mixed W/Cr oxides with different ratio of W and Cr (1:6, 1:2 and 3:2) have been prepared by using polymeric precursor method. By comparing their sensitivities to 20–300ppm NO2, it was found that the sensor using oxide with 3:2 W/Cr gave the largest response value. For 3:2 W/Cr oxide, the effect of the sintering temperature on the electrode microstructure was also investigated. As a result, the device sintered at 1000°C showed the best performance. The response value to 100ppm NO2 is 51.6mV, the response time is within 20s and the sensing device also shows an excellent selectivity against other coexisting gases. The characteristics of SEM and TEM revealed that the special microstructure of oxide electrode formed by sintering plays a significant role in better sensing performance. [Copyright &y& Elsevier]

Abstract: A series of tungstate MWO4 (M=Co, Zn and Ni) has been prepared by the polymeric precursor method. Meanwhile, yttria stabilized-zirconia (YSZ) based sensors using these oxides as sensing electrodes were investigated, and among the oxides tested, CoWO4 was found to be the most suitable for the sensing electrode (SE) of the ammonia sensor. The sensor attached with CoWO4 shows the fast response and recovery characteristics (not more than 5s respectively) and large sensitivity (−51mV/decade) at elevated temperature. The electric potential difference (∆V) of the sensor varies almost linearly with the NH3 concentrations in the examined range of 50–1000ppm. The SEM observation reveals that the special microstructure of CoWO4-SE, bulky rod-like crystals coated by tiny particles, plays a significant role in sensing performance. [Copyright &y& Elsevier]