Ethanol oxidation reaction (EOR) investigation on Pt/C, Rh/C, and Pt-based bi- and tri-metallic electrocatalysts: A DEMS and in situ FTIR study

Abstract

The ethanol oxidation reaction (EOR) was studied on Pt/C, Rh/C, Pt-Rh/C, Pt-SnO2/C and Pt-Rh-SnO2/C using on-line differential electrochemical mass spectrometry (DEMS) in a flow-cell system and in situ Fourier transform infrared spectroscopy (in situ FTIR). The electrocatalysts were synthesized by a modified polyol method and physically characterized by inductively-coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrocatalytic activity of the materials was tested for the EOR and the electrooxidation of a monolayer of adsorbed CO (COad being an intermediate of the EOR). Both in situ FTIR and DEMS investigations revealed that COad electrooxidation occurs at lower potentials on Pt-SnO2/C and Pt-Rh-SnO2/C than on Pt/C, Rh/C and Pt-Rh/C. A good correspondence was found between the (intensity vs. potential) variations of the m/z=22 mass-to-charge signal and of the IR band at 2343cm−1, both strictly assigned to CO2. The addition of Rh to Pt enhances the tolerance to adsorbed CO molecules during the EOR (CO2 molecules were detected at more negative potentials in FTIR on Rh-containing electrocatalysts), and the simultaneous presence of Pt, Rh and SnO2 in the catalysts resulted in enhanced EOR selectivity towards CO2. The CO2 current efficiency (CCE) calculations indicate quantitatively that the tri-metallic Pt-Rh-SnO2/C electrocatalyst yields more complete ethanol electrooxidation into CO2. Finally, FTIR experiments enabled to detect high-potential (E>0.95V vs. RHE) CO2 formation, which likely originates from the oxidation of either CHx- or ethoxy-adsorbates that only oxidize at high potential.