Behaviour of Pt$_{10-x}$Ru$_x$/C catalysts towards the hydrogen oxidation reaction in acidic medium in the presence of adsorbed CO
Résumé
Pt$_{10-x}$Ru$_x$/C materials are synthesised using a classical polyol method and comprehensively characterised by thermogravimetric analysis, inductively coupled plasma – optical emission spectroscopy, electron transmission microscopy and x-ray diffraction. In N$_2$-saturated electrolyte, the PtRu/C catalysts display lower onset potentials for adsorbed CO (CO$_{ads}$) removal than the pure Pt/C one. Although the surface coverages of Pt by Ru are high, the PtRu/C catalysts display higher activity than the Pt/C one towards the hydrogen oxidation reaction (HOR), but the same mechanism occurs on all the catalysts. However, when the surface of the catalysts is saturated by CO$_{ads}$, the HOR starts at a lower potential on Pt/C than on PtRu/C; Pt/C displays higher activity toward the HOR in the presence of CO$_{ads}$ between 0.40 and 0.55 V vs RHE. On Pt/C, a small part of CO$_{ads}$ desorbs into CO2 from 0.40 V through an Eley-Rideal mechanism, freeing very active Pt sites for the HOR. For potentials higher than 0.55 V vs RHE, the PtRu/C catalysts display higher activity for CO$_{ads}$ removal through the bifunctional mechanism. Ru atoms also block the most active Pt sites for the CO$_{ads}$ removal and the HOR.
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