Insight into enhanced ethanol sensing of SnOx:Ag nanoparticles by XAS

SnO2-based gas sensors have been subject of extensive academic and industrial research. The operation principle is based on the increase of material conductance in the presence of a reducing gas. Pure tin oxide suffers, however, from lack of good sensitivity and selectivity. An improvement in these two parameters has been observed by dispersing low concentrations of metallic particles (e.g. Pd, Pt, Au, Ag) in the sensing material [1, 2]. However, the role of the metal nanoparticles in the sensor response is not fully understood: chemical and electronic mechanisms are proposed. The former is focused on the ability of the metal nanoparticles to dissociate oxygen, to spill over the SnO2 surface, to catalyse the combustion of the target gas or even to reduce the SnO2 matrix. The latter on the other hand considers that the conductance changes due to the variation of contact potential at the metal nanoparticle / SnO2 interface. One of the techniques ideal for studying the sensing mechanism is XAS (X-ray Absorption Spectroscopy). Though there are reports on XAS studies of doped and undoped SnO2 thin films and nanoparticles, only few of those reports deals with the utilization of XAS for understanding the sensing mechanism of sensors based on doped SnO2. In-situ XAFS studies have been reported to get insight into the CO and H2 sensing mechanism of polycrystalline SnO2 thin films with homogeneously dispersed Pt and Pd nanoparticles. From these studies it has been concluded that whereas Pt exhibits an electronic sensing mechanism towards CO