Influence of Mono- and Bimetallic PtO(x), PdO(x,) PtPdO(x) Clusters on CO Sensing by SnO(2) Based Gas Sensors

To obtain a nanocrystalline SnO(2) matrix and mono- and bimetallic nanocomposites SnO(2)/Pd, SnO(2)/Pt, and SnO(2)/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-H(2)) methods. The sensor response of blank SnO(2) 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 SnO(2) matrix, and active surface centers. For SnO(2)/PtPd, the combined effect of the modifiers on the electrophysical properties of SnO(2) explained the inversion of sensor response from n- to p-types observed in dry conditions.