Solid-stale mixed potential gas sensors: theory. experiments and challenges

Solid-state mixed potential electrochemical sensors sense gases using diffe rential electrocatalysis on dissimilar electrode materials. The response th eory is typically expressed in terms of models invoking Butler-Volmer kinet ics at high overpotentials (Tafel behavior). This model is not adequate for describing all types of mixed potential sensor responses. For low concentr ations of analyte gas, mass transport limitations must also be considered. Experiments with sensors with air reference electrodes also demonstrate the importance of low overpotential oxygen reduction kinetics in establishing the device response. A sensor response model that predicts a linear relatio nship between response voltage and analyte gas concentration is derived. Th e development of oxide electrode based devices offers improved long-term re sponse stability over metal electrode based devices. (C) 2000 Elsevier Scie nce B.V. All rights reserved.