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Highlights: [•] La5/3Sr1/3NiO4–YSZ composite powders have been synthesized by a simple method. [•] The effect of YSZ addition on the electrode microstructure and performance was investigated. [•] The effect of sintering temperature on the electrode microstructure and performance was investigated. [Copyright &y& Elsevier]

SCR catalysts V 2 O 5 –WO 3 –TiO 2 (VWT) with various V 2 O 5 content (0–5 wt.%) were prepared by impregnation method in this work. Crystalline structures of the synthesized powder were analyzed by X-ray powder diffraction. Different VWT catalysts were used as sensing materials to prepare mixed potential ammonia sensors based on 5YSZ (ZrO 2 doped 5 mol% Y 2 O 3 ) solid electrolyte. The sensing electrodes were characterized by XRD and environmental scanning electron microscopy. NH 3 sensitivity was tested at 550 °C for the sensors with different V 2 O 5 content sensing electrodes. With the increment of V-content, the slope of semi-logarithmic characteristic curves increased but began to fall when V-content was more than 2 wt.%. High-contented V 2 O 5 promoted anatase TiO 2 grains growing up to be rod-shaped and block-shaped morphology in sintering, leading to the reduction of specific surface area. The decreased dispersion of V 2 O 5 , resulting from the growing up of the carrier TiO 2 , was responsible for the reduced activity of sensing electrode catalytic. The suitable content of V 2 O 5 in VWT catalysts for NH 3 sensors is 1–2 wt.% based on various factors. [ABSTRACT FROM AUTHOR]

NiFe 2 O 4 was synthesized using sol-gel method for sensing electrode material of YSZ based ammonia sensor. NiFe 2 O 4 -SEs sintered at 1100 °C, 1150 °C and 1200 °C were characterized by XRD, the BET method and ESEM. By testing the NH 3 response of different sensors at 650 °C, it was observed that the 1150 °C sintered sensor had the largest response value (−104.3 mV for 320 ppm NH 3) and the highest sensitivity (−77.56 mV/decade), which were related to the most TPB sites and the moderate gas phase catalytic reaction. The response values of the sensor varied almost linearly with the logarithm of 20–320 ppm NH 3 at 600–750 °C, which was consistent with mixed-potential mechanism testified by polarization and EIS tests. When the oxygen concentration was at 7–10 vol %, its effect on the response value was within 3%. When the water vapor concentration was 3, 6 and 9 vol %, the ammonia response value was 95.1%, 92.9% and 88.7% of the values when there was no water vapor, respectively. The sensor showed very weak cross sensitivities to NO x , but non-negligible SO 2 cross sensitivity. It also displayed slight signal drifts in weekly tests in eight weeks, which showed that the sensor attached with NiFe 2 O 4 -SE has a good long-term stability. Image 1 • NiFe 2 O 4 was firstly used as sensing electrode of potentiometric NH 3 sensor based on the proposed novel concept. • NH 3 sensor based on NiFe 2 O 4 -SE exhibits good selectivity and long term stability. • NiFe 2 O 4 material has a good application prospect for NH 3 detection in diesel vehicle exhaust. [ABSTRACT FROM AUTHOR]

In order to improve the microstructure and sensing property for electrode material BiVO 4 of potentiometric ammonia sensor, different MgO-doped (0, 1, 3, 5 and 8 at.%) BiVO 4 powders were synthesized by solid-state reaction method. There is no significant difference in XRD spectrum for the different powders, but the particle size of the sensing electrode has an obvious refinement with the doping of MgO. The NH 3 sensitivity of the sensor had a enhancement from 41.7 mV/decade to the highest value of 61.8 mV/decade when Mg-content reaches 5 at.%. The interfacial resistance R i between the electrode and YSZ decreases with the increment of NH 3 concentration and the Mg-doping based on impedance spectroscopy. The reduction of interface resistance is due to the enhancement of electrode reactions. The dopant MgO improves the conductivity of BiVO 4 and the TPB area, and leads to a greater charge exchange rate for the electrode electrochemical reactions. The increased specific surface area due to the grain size refinement gets more NH 3 involved in the reactions. This eventually leads to the increased sensitivity and decreased interface resistance. The optimal operating temperature is 600 °C based on the synthetical effects of various factors such as conductivity, the catalytic and gas adsorption performances of the sensing material. [ABSTRACT FROM AUTHOR]

Mixed potential ammonia sensors based on 5YSZ (ZrO 2 doped 5 mol% Y 2 O 3 ) were prepared, with ferrite CoFe 2 O 4 as sensing electrode material. Co-sintering of electrode and electrolyte has been realized. Sensors with different electrode microstructure characterized by Environmental Scanning Electron Microscope (ESEM) were made by different sintering process, and its influences on the sensors’ performance were investigated. The co-sintered sensor, with a porous three dimensional network structure electrode and great adhesion with electrolyte, exhibits the largest response (about 81 mV for 320 ppm NH 3 ) and the highest NH 3 sensitivity (55 mV/decade) with the response time (8–10 s) and recovery time (10–12 s) at 450 °C, it also shows satisfying NH 3 selectivity compared with NO x , and O 2 has few influence on the sensor responses. The enhancement of the NH 3 sensitivity may owe to the porous three dimensional network structures, which is beneficial to adsorption and diffusion of the target gas, and better bonded interface between the electrode and electrolyte also provides more quantity of triple-phase boundary (TPB). [ABSTRACT FROM AUTHOR]

Mg 2 Cu 0.25 Fe 1 O 3.75 mixed metal oxides have been synthesized by a co-precipitation method for fabricating NH 3 sensors electrodes. The sensor electrodes were sintered at 1000 °C, 1100 °C, 1200 °C, and 1300 °C to obtain different electrode microstructures. The electrodes were characterized by X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method and Environmental Scanning Electron Microscope (ESEM). NH 3 response performances of the NH 3 sensors to different concentrations of test gases (20–400 ppm NH 3 ) were evaluated at 400 °C. The influences of sintering temperature on the microstructures, NH 3 sensing performances, and electrochemically catalytic activity of Mg 2 Cu 0.25 Fe 1 O 3.75 electrodes were investigated. The electrode sintered at 1200 °C exhibited the biggest response (about 110 mV for 400 ppm NH 3 ) and the highest NH 3 sensitivity (72 mV/decade NH 3 ) of all the electrodes. Moreover, the response time and recovery time were within 8–4 s and 8–14 s, respectively. The enhanced NH 3 sensing performances of the Mg 2 Cu 0.25 Fe 1 O 3.75 electrodes may be attributed to electrodes׳ larger electrochemically catalytic activity and more quantity of triple-phase boundary (TPB) of the sintered three-dimensional network electrode structure. [ABSTRACT FROM AUTHOR]

In this work, a (La0.8Sr0.2)2FeNiO6−δ (LSFN) powder semiconductor oxide with a double-perovskite structure was synthesized by a polymeric precursor method to fabricate a sensitive electrode (SE) for a NO x sensors based on yttria-stabilized zirconia (YSZ). The LSFN powder and the LSFN-SEs sintered at different temperatures (1000, 1100 and 1200°C) were characterized by X-ray diffraction (XRD). The morphologies of LSFN-SEs were observed by environmental scanning electron microscopy (ESEM). The sensors with LSFN-SEs were tested over a temperature range of 550–800°C. Electrochemical impedance spectroscopy (EIS) was also performed to investigate the electrochemical processes that are affected by the NO2 concentration. The results demonstrated that the double-perovskite type electrode material possessed good thermal stability. The NO2 sensitivity of the sensor was found to be modulated by the morphology of LSFN–SE. The sensor showed a higher sensitivity and a better selectivity to NO2 than that to NO. The impedance changed when the NO2 concentration was varied, which was attributed to the interaction of the NO2 with the SE. [ABSTRACT FROM AUTHOR]

LaNbO 4 powder was synthesized and first used as sensing material to fabricate potentiometric sensor in the field of carbon monoxide (CO) detecting. The XRD spectrums of LaNbO 4 electrodes sintered at different temperatures showed basically no obvious difference, while the porous network and the most TPB sites were obtained at 1100 °C, bringing the best sensing performance which includes sensitivity of −87.25 mV/decade and a swift response/recovery process within 47/52 s to 400 ppm CO. The response values all take on an approximately linear trend with logarithm of CO concentration from 50 ppm to 400 ppm, which agrees well with the mixed-potential mechanism. The sensor exhibited the most comprehensive sensing properties to CO when operating at 400 °C, and polarization and EIS measurements were then evaluated for the analysis of response mechanism. Moreover, the slight sensitivities to interfering gases like NO x indicated a good selectivity of the sensor, and the response value was also less affected by the oxygen concentration and water vapor. Given the satisfied response signal and swift response/recovery processes, good CO selectivity, adequate stability in repetitive and prolonged test, LaNbO 4 is promising in monitoring CO as a sensing material adopted by potentiometric sensor. • LaNbO 4 was firstly used as an electrode material of mixed-potential CO gas sensor. • The sensor based on LaNbO 4 electrode exhibited fast response/recovery process, excellent selectivity and long-term stability. • LaNbO 4 material has a promising application prospect in the field of CO detection in automobile exhaust. [ABSTRACT FROM AUTHOR]

• InVO 4 was first applied to the sensing electrode for potentiometric ammonia sensor. • The sensor has considerable sensitivity of -86.7 mV/decade and response value of −143 mV to 320 ppm NH 3 at 600 °C. • The sensor with InVO 4 electrode exhibits good NH 3 sensitivity, selectivity and durability. Orthorhombic InVO 4 powder was synthesized by precipitation method and sintered at 900, 1000 and 1100 °C to prepare the sensing electrodes for potentiometric ammonia sensors. The influence of sintering temperature on electrode morphology and NH 3 sensing properties was investigated at 600 °C operating temperature. With the increase of sintering temperature, the layer thickness decreases and porosity increases for InVO 4 electrode. The resulting reduction of gas-phase consumption of NH 3 and the increment of three-phase boundary (TPB) enhance the NH 3 sensitivity from −79.9 mV/decade of 900 °C to −86.7 mV/decade of 1000 °C. The 1100 °C-sintered sensor has the lowest sensitivity of −25.9 mV/decade due to the TPB reduction caused by over-loosened electrode from more intense sintering. The response and recovery times decrease from 68 s and 151 s for 900 °C-sintered sensor to 19 s and 29 s for 1100 °C-sintered sample. The highest NH 3 response is obtained at 600 °C with the response values of −143 mV to 320 ppm and −13 mV to 10 ppm NH 3. The recovery rate accelerates with increase of operating temperature from 550 to 650 °C, but response rate slows down. The low cross-sensitivity to various gases especially NO x indicates good NH 3 selectivity of the sensor due to the outstanding electrocatalytic activity of InVO 4 for NH 3 oxidation electrode reaction. Considered the good NH 3 sensitivity, selectivity, repeatability, durability and resistance to oxygen/vapor interference, it is believed that InVO 4 is a promising ammonia sensing electrode material. [ABSTRACT FROM AUTHOR]