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

Yttria-stabilized zirconia (YSZ)-based amperometric NO(2) sensors comprised of an In(2)O(3) sensing-electrode (SE), a Pt counter-electrode (CE) and a Mn(2)O(3) reference-electrode (RE) in both tubular and rod geometries were fabricated and their sensing characteristics were examined. For comparative purposes, the performance of the In(2)O(3)-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 Mn(2)O(3)-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 Mn(2)O(3)-RE can successfully replace the Pt/air-RE in an amperometric gas sensor. Similarly, rod-type sensors utilizing an In(2)O(3)-SE and a Mn(2)O(3)-RE were observed to have almost identical NO(2) sensing characteristics to that of the tubular sensor. Furthermore, both sensors (tubular or rod geometry) exhibited a linear response to increasing NO(2) concentration in the range of 20-200 ppm at 550°C.