Palladium embedded in SnO2 enhances the sensitivity of flame-made chemoresistive gas sensors

Abstract

Palladium is used commonly to enhance the performance of chemoresistive metal-oxide gas sensors. Typically, this enhancement is attributed to the presence of Pd clusters on the surface of their metal-oxide support (i.e. SnO₂). Possible Pd incorporation or embedding into the support rarely has been considered. Here, SnO₂ particles (15 - 21 nm in diameter measured by N₂ adsorption) with different Pd contents (0 - 3 mol%) were prepared by flame spray pyrolysis (FSP). Leaching these particles with HNO₃ and characterization by inductively coupled plasma - optical emission spectrometry (ICP-OES) indicated that only 36 - 60% of Pd have been removed (e.g., from the SnO₂ surface). The rest was embedded within the SnO₂ particles. Annealing prior to leaching decreased by ~30% that Pd surface content. Most interestingly, such SnO₂ particles (with only embedded Pd) show higher sensor response to acetone, ethanol and CO at 350 °C compared to SnO₂ particles containing both surface and embedded Pd (i.e. before leaching). As a result, such sensors can detect acetone with high (> 25) signal-to-noise ratio at levels down to 5 ppb at 50% relative humidity. Graphical abstractFlame-made SnO₂ nanoparticles with embedded and surface Pd (triangles) exhibit lower sensor response to acetone, ethanol and CO than SnO₂ from which the surface Pd had been removed by leaching (circles).

Keywords: Breath analysis; Doping; Environmental monitoring; Flame spray pyrolysis; Noble metal; Semiconductor; Solid-state, chemiresistive gas sensors; Surface clusters.