Influence of Mono- and Bimetallic PtOx, PdOx, PtPdOx Clusters on CO Sensing by SnO₂ Based Gas Sensors.

To obtain a nanocrystalline SnO₂ matrix and mono- and bimetallic nanocomposites SnO₂/Pd, SnO₂/Pt, and SnO₂/PtPd, a flame spray pyrolysis with subsequent impregnation was used. The materials were characterized using X-ray diffraction (XRD), a single-point BET method, transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The electronic state of the metals in mono- and bimetallic clusters was determined using X-ray photoelectron spectroscopy (XPS). The active surface sites were investigated using the Fourier Transform infrared spectroscopy (FTIR) and thermo-programmed reduction with hydrogen (TPR-H₂) methods. The sensor response of blank SnO₂ and nanocomposites had a carbon monoxide (CO) level of 6.7 ppm and was determined in the temperature range 60⁻300 °C in dry (Relative Humidity (RH) = 0%) and humid (RH = 20%) air. The sensor properties of the mono- and bimetallic nanocomposites were analyzed on the basis of information on the electronic state, the distribution of modifiers in SnO₂ matrix, and active surface centers. For SnO₂/PtPd, the combined effect of the modifiers on the electrophysical properties of SnO₂ explained the inversion of sensor response from n- to p-types observed in dry conditions.