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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]

V 2 O 5 -WO 3 -TiO 2 mixed metal oxide catalyst was synthesized by impregnation method for fabricating sensing electrodes of potentiometric ammonia sensor in this paper. The sensing electrodes were sintered from 650 °C to 900 °C to obtain different electrode microstructures. Crystalline structures of the sensing materials were analyzed by X-ray powder diffraction, and the sensing electrode microstructures were characterized by environmental scanning electron microscopy. Sintering temperature strongly affects the microstructure and the sensitivity of the sensing electrode. With the increment of sintering temperature, the slope of semi-logarithmic characteristic curves increased but began to fall when temperature was more than 750 °C. The effect of sintering temperature on the response and recovery property has similarities, the sensors sintered at 750 °C and 700 °C show the shortest response/recovery times. The increase of the sintering temperature is beneficial for a stronger bond between sensing electrode and YSZ electrolyte, and this could increase the amount of three-phase boundary, and improve the sensor performance. High temperature promotes the V 2 O 5 volatilization, anatase TiO 2 grains growing up and the anatase to rutile phase transition, further cause the reduction of the electrode specific surface area. The volatilization of V 2 O 5 and the destruction of high dispersion V 2 O 5 resulted from the growing up of the carrier TiO 2 , are responsible for the degraded properties of sensing electrode. The suitable operating temperature for this type NH 3 sensor is 550 °C based on the compromise of various factors which could influence the sensor performance. [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]

• 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]

• The NH 3 sensing properties are affected by operating temperature and oxygen content. • The sensing property is greatly enhanced after the electrode morphology regulation. • The broken line-shaped sensitivity curve is caused by the gas-phase consumption of ammonia with oxygen. The influences of sensing electrode morphology, operating temperature and the oxygen content on NH 3 sensing properties for the potentiometric gas sensor attached with CeVO 4 sensing electrode were studied. With the increase of electrode sintering temperature, CeVO 4 grains grow up gradually. The response/recovery time shows a decreasing trend, but the NH 3 sensitivity reaches the highest when the sintering temperature reaches 1000 °C, this was determined by the amount of TPB and the ammonia concentration involved in the electrode electrochemical reactions. The NH 3 sensitivity enhances with the increase of operating temperature in the range of 450–550 °C and presents the mixed-potential characteristic. When the temperature exceeds 600 °C, the curve between ΔV and logarithm of NH 3 concentration presents a broken line relationship, and the concentration corresponding to the inflection point increases with the increase of operating temperature. The response and recovery rates accelerate but the NH 3 sensitivity decreases with the increase of oxygen content in testing gas. When the oxygen is above 10 vol.% and NH 3 is below 80 ppm, the response value is almost unaffected by the change of oxygen concentration. The broken line feature of the sensitivity curve under high operating temperatures and oxygen concentrations is mainly related to the gas phase catalytic reaction of NH 3 by oxygen. [ABSTRACT FROM AUTHOR]