Adsorption of Carbon Monoxide on Platinum–Ruthenium, Platinum–Osmium, Platinum–Ruthenium–Osmium, and Platinum–Ruthenium–Osmium–Iridium Alloys

Abstract

Ternary and quaternary PtRuOs and PtRuOsIr alloys are promising alternatives to the binary PtRu alloys that serve as efficient anode catalysts for methanol and hydrogen air fuel cells. The efficiency of these catalysts is correlated to the adsorption of CO molecules on their surfaces. In this work, we study CO adsorption on a series of PtRu, PtOs, PtRuOs, and PtRuOsIr alloys and on pure Pt, Os, Ir, and Ru using periodic density functional theory. Systematically, we vary the location of the alloy atoms in the substrate and the alloy Pt mole percent. As CO is adsorbed on PtRu, PtRuOs, and PtRuOsIr alloys, the CO internal adsorbate bond and the C–Pt surface bond weaken on average (for alloy configurations of the same Pt mole percent) along with the decrease of the Pt mole fraction in the alloy. However, the frozen substrate calculations show that these bonds are about invariant of alloying Pt with Os atoms, with the exception of PtOs configurations with Os atoms in the middle layer, whereas relaxing the substrate surface may lead to stronger C–O and C–Pt bonds due to alloying Pt with Os. The C–O and C–Pt overlap populations are correlated with the carbon s-type vacancies and the overall s, p, and d vacancies of the adsorbing metal, for the C–O and C–Pt bonds, respectively: Hybridization defects are attributed to the cases of concomitant increase of the overlap populations and downshifts of the corresponding stretching frequencies. Changes in the CO internal adsorbate bond are explained using a phenomenological model based on the modified π-attraction σ-repulsion scheme and is compared with the traditional 5σ donation–2π* back-donation mechanism. This model successfully ascribes the C–O internal adsorbate bond strength to the carbon and oxygen atom contributions of the σ and π hybrid CO-substrate orbitals for the majority of the systems examined here.

A quantum chemical study of substituent effects on CN bonds in aryl isocyanide molecules adsorbed on the Pt surface

“…Therefore, we examine the electron transfer process during the formation of a chemical bond This newly presented model has been used to explicitly explain the C−O and C−metal bond strengths of CO adsorbed on Pt−Os binary alloy and Pt−Ru−Os tertiary alloy, 82 and PtRuOsIr quaternary, 83 on PtRu alloys, 84 and Pt(100) and Ru(0001) surfaces, 85 as well as water and CO coadsorbed on Pt(111) surface at various coverages. 86 To characterize the substituent effect on the NC stretching frequency and bond order concisely, we discuss the donation and back-donation strengths based on a localized perspective of chemical bonding in a quantitative manner.…”

Li and Na Adsorption on Graphene and Graphene Oxide Examined by Density Functional Theory, Quantum Theory of Atoms in Molecules, and Electron Localization Function

“…Here, we only report BSSE corrected E ads and E c values. Calculated E ads and E c values using the counterpoise correction are less negative in energy than corresponding uncorrected values [ 17 , 49 , 67 ].…”

Structural Evolution and Magnetic Properties of Gd2Hf2O7 Nanocrystals: Computational and Experimental Investigations

“…Details regarding the Brillouin zone integrations grids can be found in the Supplementary Materials . SCF energy convergence and geometry optimization parameters are described in our past work [ 66 , 67 ].…”