Mathias Christian Stranzenbach

Planar, Impedance-Metric NOX Sensor with NiO Sensing Electrode for High Temperature Applications

In this study, an innovative type of sensor configuration is used which contains an electrolyte constructed of quasi-single crystalline columns, a porous NiO sensing electrode (SE) and a conductive Pt reference electrode (RE) deposited on the backside. As electrolyte EB-PVD manufactured discs of FYSZ and PYSZ composition were used. Gas sensing characterization of the sensors was carried with typical flue-gas mixtures in various concentrations. Impedance and potential analysis were done at a frequency range of 100 kHz and 0.005 Hz. Sensors with FYSZ electrolyte could be operated at higher temperatures compared to those with PYSZ electrolytes. The highest achieved sensing temperature in this study was 600degC. NO was successfully detected under the presence of 5%vol. O2 at the maximum operating temperature.

Electrochemical high-temperature gas sensors

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.