Effects of Ag Additive in Low Temperature CO Detection with In₂O₃ Based Gas Sensors.

Nanocomposites In₂O₃/Ag obtained by ultraviolet (UV) photoreduction and impregnation methods were studied as materials for CO sensors operating in the temperature range 25⁻250 °C. Nanocrystalline In₂O₃ and In₂O₃/Ag nanocomposites were characterized by X-ray diffraction (XRD), single-point Brunauer-Emmet-Teller (BET) method, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The active surface sites were investigated using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy and thermo-programmed reduction with hydrogen (TPR-H₂) method. Sensor measurements in the presence of 15 ppm CO demonstrated that UV treatment leads to a complete loss of In₂O₃ sensor sensitivity, while In₂O₃/Ag-UV nanocomposite synthesized by UV photoreduction demonstrates an increased sensor signal to CO at T < 200 °C. The observed high sensor response of the In₂O₃/Ag-UV nanocomposite at room temperature may be due to the realization of an additional mechanism of CO oxidation with participation of surface hydroxyl groups associated via hydrogen bonds.