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 conduct ive whiskers, iron phthalocyanine and PbSnF4), shows a linear I-sc (short-c ircuit current)-{P-O2(O-2 partial pressure)}(1/2) relation and a Nernst-typ e emf-P-O2 relation (the number of the associated electrons approximate to 2). The SE-reaction thus occurs as follows: O-2 --> 2O, O + e(-) --> O-. Un der short-circuit (sc) condition, the rate-determining step is the charge-t ransfer step of the reduction, because the I-E characteristics of the SE ex hibit 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 additio n to this, the very low level of I-sc permits the reproducible response wit h a long-term stability. (C) 2000 Elsevier Science S.A. All rights reserved .