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Combustion produced common air pollutant, NOx associates with greenhouse effects. Its high temperature detection is
essential for protection of nature. Component-integration capable high-temperature sensors enable the control of
combustion products. The requirements are quantitative detection of total NOx and high selectivity at temperatures above
500°C.
This study reports various approaches to detect NO and NO2 selectively under lean and humid conditions at temperatures
from 300°C to 800°C. All tested electrochemical sensors were fabricated in planar design to enable componentintegration.
We suggest first an impedance-metric gas sensor for total NOx-detection consisting of NiO- or NiCr2O4-SE
and PYSZ-electrolyte. The electrolyte-layer is about 200μm thickness and constructed of quasi-single crystalline
columns. The sensing-electrode (SE) is magnetron sputtered thin-layers of NiO or NiCr2O4. Sensor sensitivity for
detection of total NOx has been measured by applying impedance analysis. The cross-sensitivity to other emission gases
such as CO, CO2, CH4 and oxygen (5 vol.%) has been determined under 0-1000ppm NO. Sensor maintains its high
sensitivity at temperatures up to 550°C and 600°C, depending on the sensing-electrode. NiO-SE yields better selectivity
to NO in the presence of oxygen and have shorter response times comparing to NiCr2O4-SE.
For higher temperature NO2-sensing capability, a resistive DC-sensor having Al-doped TiO2-sensing layers has been
employed. Sensor-sensitivity towards NO2 and cross-sensitivity to CO has been determined in the presence of H2O at
temperatures 600°C and 800°C. NO2 concentrations varying from 25 to 100ppm and CO concentrations from 25 to
75ppm can be detected. By nano-tubular structuring of TiO2, NO2 sensitivity of the sensor was increased.
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