Exploring characteristics of palladium-loaded tin (IV) oxide nanohybrids towards chemiresistive gas sensing

Nanocrystalline pristine and Pd-loaded tin (IV) oxide (SnO2) nanocomposites with different loadings were synthesized via facile impregnation and in-situ reduction, followed by annealing. The crystal structure and morphology of the samples were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. X-ray photoelectron spectroscopy, Raman spectroscopy and ex-situ extended X-ray absorption fine structure (EXAFS) confirm PdO nanoclusters stabilized on SnO2 surface. Results revealed that Pd/ SnO2 with 2.8 wt% loading exhibits the best sensing performance, including high sensitivity to CO with a low detection limit, fast response, and good selectivity to CO against interfering gases. Its enhanced sensing performance is attributed to both fine structure of PdO, and the synergy between PdO and SnO2 as well as dissimilar defect structures and concentrations. In-situ FTIR measurements unraveled CO adsorption kinetics on Pd/SnO2 under reaction conditions, based on which a possible sensing mechanism is put forth. Namely, Pd and PdO on edges, steps, and terraces of (100) and (111) facets provide favorable adsorption and activation sites for CO, from which activated fragments are spilled over onto SnO2 to react with ionosorbed oxygen, locally decreasing depletion layer and sensor resistance; and concurrently, carbon-related species are formed and decomposed into CO2.