In Situ Characterization of Ternary Pt-Rh-SnO2/C Catalysts for Ethanol Electrooxidation

Carbon-supported ternary Pt-Rh-SnO2 electrocatalysts with two different stoichiometries (i.e. Pt23Rh5Sn26/C and Pt21Rh5Sn39/C) were synthesized using a two-step sequential approach. Characterization of the catalysts was conducted by a range of techniques. X-ray diffraction (XRD), together with high resolution transmission electron microscope (HR-TEM) studies showed that the obtained electrocatalysts were composed of two categories of nanoparticles: PtRh solid solution and SnO2. Electrochemical measurements showed that both ternary catalysts demonstrated superior performance over the conventional Pt/C and PtRu/C catalysts for ethanol electrooxidation reaction (EOR). Between the two catalysts, the one having lower SnO2 content (i.e. Pt23Rh5Sn26/C) exhibited the higher activity and greater stability. In situ X-ray absorption spectroscopy (XAS) studies revealed structural information of the nanocatalysts, including bond distances, coordination numbers, and stoichiometry consistent with independently obtained inductively coupled plasma-optical emission spectroscopy (ICP-OES) data. The results suggested that a metal-metal oxide interaction in the ternary Pt-Rh-SnO2 system with higher oxide (i.e. SnO2) content has caused the increase in oxidation state of both Pt and Rh, which may explain the lower activity of the catalyst for EOR.