Sensing behavior of YSZ-based amperometric NO2 sensors consisting of Mn-based reference-electrode and In2O3 sensing-electrode

Yttria-stabilized zirconia (YSZ)-based amperometric NO2 sensors comprised of an In2O3 sensing-electrode (SE), a Pt counter-electrode (CE) and a Mn2O3 reference-electrode (RE) in both tubular and rod geometries were fabricated and their sensing characteristics were examined. For comparative purposes, the performance of the In2O3-SE and Pt-CE were also examined against an internal Pt/air-RE. Experimental observations of tubular YSZ-based gas sensors revealed that a three-electrode system exhibited better electrical signal stability, when compared with a two-electrode system. Additionally, replacing the internal Pt/air-RE with an external Mn2O3-RE (exposed to the sample gas), was found to have a negligible effect on the gas sensing characteristics of the tubular sensor. This gas sensing equivalence indicates that Mn2O3-RE can successfully replace the Pt/air-RE in an amperometric gas sensor. Similarly, rod-type sensors utilizing an In2O3-SE and a Mn2O3-RE were observed to have almost identical NO2 sensing characteristics to that of the tubular sensor. Furthermore, both sensors (tubular or rod geometry) exhibited a linear response to increasing NO2 concentration in the range of 20–200 ppm at 550 °C.