Ethanol and Methanol Electrolysis at Core-Shell Ru@Pt and PtRu@Pt Catalysts with Different Pt Shell-Thickness

Abstract

One of the attractive methods used to prepare hydrogen gas is the electrolysis of alcohols such as methanol and ethanol in a proton exchange membrane (PEM) cell. Platinum is the most common catalyst used to provide high selectivity for C-C bond cleavage for ethanol, leading to an increase in the amount of hydrogen gas produced. However, the cost of the Pt and poisoning of the surface by the adsorbed CO intermediate limit its use. Combining Pt with other metals such as ruthenium in the form of core-shell nanoparticles enhances its ability for alcohol oxidation [1,2]. Therefore, more hydrogen gas is evolved in a PEM electrolysis cell, especially at lower applied potentials. In addition, these modified catalysts can be used in the anodes of direct alcohol fuel cells.Here, we aimed to prepare Pt-based core-shell nanoparticles in which commercial catalysts PtRu and Ru were used as the core, and different amounts of Pt were deposited on their surface as a shell (PtRu@Pt and Ru@Pt). These catalysts were prepared using the polyol method without adding any stabilizer that would block their surface and affected their alcohol oxidation activity. The formation of these core-shell nanoparticle catalysts was confirmed by using thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy with an energy dispersive X-ray analyzer, X-ray diffraction and X-ray photoelectron spectroscopy. Moreover, the effect of the Pt thickness on methanol and ethanol electrochemical oxidation was studied using cyclic voltammetry at room temperature and a PEM electrolysis cell at 80 °C.Results show that methanol and ethanol oxidation activity increased greatly as the thickness of the Pt shell was increased, although the half potential was shifted to a higher potential. Moreover, the addition of the Pt to the shell increased the limiting current, indicating that the selectivity toward CO2 formation increased and that more hydrogen was being produced. Finally, Ru as a core showed a lower improvement for methanol oxidation than PtRu. However, Ru@Pt catalysts with more than one Pt monolayers gave higher ethanol oxidation performances than the PtRu@Pt catalysts. Acknowledgments This work was supported by the Natural Science and Engineering Research Council of Canada and Memorial University.