Analysis of the selectivity of PtRh/C and PtRhSn/C to the formation of CO₂ during ethanol electrooxidation

Highlights: • Ethanol oxidation on PtRh produces proportionally more CO₂ on Rh richer surfaces. • However, ethanol oxidation currents decrease upon these conditions. • This deactivation is probably due to a slow kinetics of adsorption of ethanol on Rh. • Conversely, PtRhSn shows higher activity toward ethanol oxidation compared to PtRh. • However, Sn promotes a non-selective oxidation rather than a driven CO₂ production. - Abstract: PtRh and PtRhSn electrocatalysts of different atomic compositions were prepared by dispersion on carbon Vulcan XC-72R using the polyol reduction method and characterized by energy dispersive X-ray analysis, X-ray diffraction and transmission electron microscopy. The electrooxidation of ethanol was investigated in acid medium by cyclic voltammetry, chronoamperometry and in situ Fourier transform infrared spectroscopy (FTIR) experiments. Results showed that the electrochemical response in presence of ethanol is strongly influenced by the composition of the catalyst. The in situ FTIR results allowed correlating the electrochemical response with the formation of CO₂ and acetic acid and suggest that although there is anticipation in the formation of both species, the presence of Rh is deleterious for the electrocatalytic activity of the binary electrodes (at least for the compositions range investigated), probably due to the slow kinetics of adsorption of ethanol on Rh. Conversely, the ternary catalyst (Pt₆₁Rh₀₉Sn₃₀/C) facilitates both adsorption and oxidation steps which explain the higher currents observed in the voltammetric and chronoamperometric experiments. However, Sn seems not to drive the reaction toward the production of CO₂, and the electrocatalysis is better explained by a non-selective oxidation process