Activity, mechanism, and short-term stability evaluation of PtSn-rare earth/C electrocatalysts for the ethanol oxidation reaction
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Rare earths (RE) have been studied in the literature as additives in Pt and PtSn catalysts for the ethanol oxidation reaction (EOR), but their stability and influence on the mechanism of the EOR have not been reported. In this work, PtSnRE/C (RE: La, Ce, and Pr) catalysts were obtained by the polyol method, characterized, and their stability toward the EOR evaluated by cycling at two different potential ranges. The accelerated aging tests indicated that despite the changes in the CO stripping profiles, the ternary catalysts exhibit higher current densities after aging than Pt/C and PtSn/C catalysts. Even after dissolution of the rare-earth metals, as observed by energy-dispersive X-ray spectroscopy (EDS) before and after aging, the EOR activity after short-term stability tests was found to be higher than the initial one. The addition of these metals facilitates the retention of tin in the material, contributing to the overall stability of the bimetallic catalyst. The oxidation products of the ternary catalysts were evaluated by in situ Fourier transform infrared spectroscopy (FTIR) spectroscopy and high-performance liquid chromatography (HPLC), where the major products were found to be acetaldehyde and acetic acid, with only small concentrations of CO2. The improvement in the ethanol oxidation efficiency by PtSnRE/C catalysts can be explained by a bifunctional mechanism in which the rare-earth oxides are able to provide oxygenated species at low potentials.
KeywordsRare earths Platinum Tin Ethanol oxidation reaction Short-term stability
The authors thank the São Paulo Research Foundation (FAPESP) for the resources (2013/16930-7) and for the fellowships granted (2012/12189-8; 2015/13218-0).
FAPESP grant #2013/16930-7, #2012/12189-8; and #2015/13218-0.
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