| Summary: | Perovskite-type mixed-metal oxides are of particular interest as semiconductor gas sensors due to the variability in the material composition and the stability of sensing parameters. LaFeO<sub>3</sub> is a <i>p</i>-type semiconductor with relatively high conductivity and gas sensitivity. However, less is known about the sensitivity and sensing mechanisms of LaFeO<sub>3</sub> modified by catalytic noble metals. In this work, we used a microwave-assisted sol–gel method to synthesize perovskite LaFeO<sub>3</sub> nanoparticles with an average size of 20–30 nm and a specific surface area of 6–8 m<sup>2</sup>/g. LaFeO<sub>3</sub> was modified by 2–5 wt.% Ag and Pd nanoparticles via the impregnation route. Using X-ray photoelectron spectroscopy, the additives were observed in the partially oxidized states Ag<sub>2</sub>O/Ag and PdO/Pd, respectively. Electric conduction and sensitivity to noxious gases were characterized by electrophysical measurements. It was shown that LaFeO<sub>3</sub> modified by Ag and Pd had improved sensitivity and selectivity to CO, and the sensing behavior persisted in a wide range of relative humidity. Pristine and Ag-modified LaFeO<sub>3</sub> had the maximum sensitivity to CO at a temperature of 200 °C, while modification with Pd resulted in a decreased optimal operating temperature of 150 °C. In situ infrared spectroscopy revealed that supported Pd nanoparticles specifically catalyzed CO oxidation at the surface of LaFeO<sub>3</sub> at room temperature, which was the likely reason for the improved sensitivity and decreased optimal operating temperature of LaFeO<sub>3</sub>/Pd sensors. On the other hand, Ag nanoparticles were deduced to activate CO oxidation by lattice oxygen at the surface of LaFeO<sub>3</sub>, providing enhanced CO sensitivity at a higher temperature.
|
|---|
