Time-dependence of the conductance of SnO 2: Pt: Sb in atmospheres containing oxygen, carbon monoxide and water vapour I. Non-oscillatory behaviour

Abstract

The time-dependence of the conductance G( t) of SnO 2: Pt: Sb gas sensors after introducing CO in atmospheres containing oxygen and water vapour was investigated. Depending on experimental conditions, different G( t) behaviours were observed over different temperature ranges: either monotonic increases towards steady-state values, or self-sustained oscillations. Part I describes and analyzes the non-oscillatory behaviour, Part II the oscillatory behaviour. A unitary model is proposed, which offers a qualitative explanation for both, by taking into account an assembly of interdependent surface phenomena, including adsorption, desorption, spill-over and chemical reactions of oxygen, carbon monoxide and water. The role of water vapour is emphasized. Though speculative, the model is consistent with a broad range of experimental results and it also allows for some general considerations about utilizing the SnO 2: Pt: Sb material as CO sensor and as oxidation catalyst.