Construction and Working Mechanism of Sulfur Dioxide Sensor Utilizing Stabilized Zirconia and Metal Sulfate

Abstract

An exploratory study was carried out to elucidate the fabrication principles of a potentiometric sensor utilizing stabilized zirconia (solid electrolyte) and a metal sulfate (auxiliary phase). Among the MgO‐, CaO‐, ‐stabilized zirconia (abbreviated as MSZ, CSZ, or YSZ) tested, only MSZ samples which contained 15 mole percent (m/o) MgO and were partially stabilized gave a stable sensor by being attached with , whereas almost fully stabilized MSZ (15 m/o MgO), partially stabilized MSZ (9 m/o MgO), CSZ (11 m/o CaO), or YSZ (8 m/o ) gave a stable device only when attached with a mixed auxiliary phase of . These facts indicated an active role by MgO, either segregated from the stabilized zirconia or added intentionally, for the devices. It is estimated that, together with and , MgO is an essential component of the interfacial compound which acts as an ionic bridge between stabilized zirconia ( conductor) and auxiliary phase ( conductor). The electromotive force (EMF) response of each device to followed Nernst's equation well for a two‐electron reaction per molecule, while the EMF dependence on oxygen concentration deviated slightly from the Nernstian behavior for the four‐electron reduction of . Such behavior is discussed based on the sensing mechanism proposed.