Role of Pd nanoparticles in gas sensing behaviour of Pd@In2O3 yolk–shell nanoreactors

Abstract

Pd@In₂O₃ yolk–shell nanoparticles (NPs) were synthesized by a simple solution route using Pd@C core–shell NPs as template and applied for gas sensing. A glucose-assisted hydrothermal method was used for the synthesis of Pd@C core–shell NPs. Pd@In₂O₃ yolk–shell NPs were formed after calcination (450 °C for 3h) of Pd@C core–shell NPs containing indium precursor. In the Pd@In₂O₃ yolk–shell geometry, about 50–70 nm Pd NPs were present at the periphery of an In₂O₃ shell (10–20 nm thickness). The In₂O₃ shell was composed of ∼10 nm primary particles. The role of Pd NPs in gas sensing behavior of In₂O₃ has been investigated. The loading of In₂O₃ with Pd NPs improved the response for reducing gases, but reduced the response for oxidizing gases. The response of Pd@In₂O₃ yolk–shell NPs to ethanol was approximately 14 times higher than that of pure In₂O₃ hollow nanospheres at 350 °C. However, no response was recorded for NO₂ for Pd@In₂O₃ as compared to In₂O₃ (resistance ratio R_s = 2.50) at 350 °C. The maximum response of Pd@In₂O₃ yolk–shell NPs to 5 ppm ethanol was 159.02 at 350 °C, which was approximately 2.5 times higher than those for other interfering gases (NO₂, p-xylene, trimethylamine, HCHO, CO and H₂). The effect of humidity on the gas sensing characteristics of Pd@In₂O₃ yolk–shell NPs suggested that the present sensor can be used to detect ppm-level ethanol even in highly humid atmosphere (80% RH). The improved gas sensing performance of Pd@In₂O₃ yolk–shell NPs was attributed to catalytic activity of Pd NPs as well as hollow spaces that allowed the accessibility of Pd NPs to gas molecules.