Development of a solid state sensor for nitrogen oxides with a nitrate electrolyte

Nitrogen oxides play an important role in combustion processes, as a metabolite in the human body, and in air in troposphere as well as in stratosphere. Solid electrolytes are well-suited for high-temperature electrochemical devices and have shown high potential for many applications in industry and automotive applications. Such NOx sensors mostly based on alkaline nitrate electrolyte are used in potentiometric mode, so far. In this paper, the newly developed NOx sensor is described which is based on barium nitrate composites as an electrolyte which works in an amperometric mode. That sensor made of thick film technique was investigated respecting the chemical and thermodynamic stability of the barium nitrate solid electrolyte, the optimal operation temperature, sensitivity and long-term stability. Due to the required high accuracy in temperature determination and regulation, three different temperature measurement techniques in the range of 100–1000 °C have also been investigated. The sensor works in the NOx concentration range of 1–90 ppm between 320 and 480 °C. The cross sensitivity towards oxygen was observed, whereas CO2 in small concentrations does not influence the sensor signal at 360 °C.