Response mechanism of amperometric oxygen sensors with PbSnF4 electrolyte and whisker-containing sensing electrode

The sensor, Ag|Ag6I4WO4|PbSnF4|sensing electrode (SE: a mixture of conductive whiskers, iron phthalocyanine and PbSnF4), shows a linear Isc (short-circuit current)–{PO2 (O2 partial pressure)}1/2 relation and a Nernst-type emf–PO2 relation (the number of the associated electrons≈2). The SE-reaction thus occurs as follows: O2→2O, O+e−→O−. Under short-circuit (sc) condition, the rate-determining step is the charge-transfer step of the reduction, because the I–E characteristics of the SE exhibit a Tafel relation in −400 to +100 mV vs. Ag|Ag6I4WO4. The SE-potential is always fixed at that of the Ag electrode under SC condition. In addition to this, the very low level of Isc permits the reproducible response with a long-term stability.