DFT study of chlorine adsorption on bimetallic surfaces - Case study of Pd3M and Pt3M alloy surfaces

• Cl adsorption was analyzed on various Pd3M and Pt3M alloy surfaces.
• The Pd-based surfaces bind chlorine more strongly than the Pt-based surfaces.
• Charge transfer to Cl adsorbate depends on the nature of solute metals.
• The degree of bond ionicity is below 20% in all studied cases.
• Adsorption trends were related to charge transfer and surface electronic structure.

Chlorine adsorption on Pd3M and Pt3M alloy surfaces (M = Fe, Co, Ni, Rh, Pd, Pt) with ideal bulk surface composition and Pt and Pd-skin type surfaces was analyzed by means of spin-polarized periodic Density Functional Theory calculations. The Pd-based surfaces tended to adsorb chlorine more strongly than the Pt-based surfaces. On bimetallic surfaces, Cl preferred to adsorb on the high-coordination sites. The ratio of surface stabilities, that is the preference of non-segregated surfaces or the skin-type ones, can be inverted under chlorine chemisorption conditions. The relative surface stability was linked to catalytic activity of Pt3Ni surfaces towards the oxygen reduction reaction in chloride-containing solutions. The charge transfer from metallic substrate to the Cl adatom was found to become more pronounced when the position of the solute M in the Periodic Table of Elements moved upward and left. However, the degree of bond ionicity did not exceed 20% in any case. In order to contribute to the comprehension of the adsorption trends, the Cl adsorption energy was correlated to the charge transfer parameters and to the electronic structure of the investigated bimetallic surfaces.

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