First principles study of oxygen adsorption on Se-modified Ru nanoparticles

Area of Science:

• Computational materials science
• Surface chemistry
• Electrocatalysis

Background:

• Selenium/Ruthenium (Se/Ru) nanoparticles are investigated as potential electrocatalysts for the oxygen reduction reaction (ORR) in direct methanol fuel cells.
• Oxygen binding energy is a key descriptor for catalyst activity in the ORR.

Purpose of the Study:

• To investigate the electronic and geometric structures and energetics of Se and O adsorption on Ru nanoparticles using density-functional theory (DFT).
• To understand the effect of Se modification on O binding and its implications for ORR activity.

Main Methods:

• Density-functional theory (DFT)-based calculations.
• Simulation of Se and O adsorption on 93- and 105-atom Ru nanoparticles.

Main Results:

• Se bonding on flat Ru facets is ionic, similar to Se/Ru(0001) surfaces, while low-coordinated Ru sites show some covalent contribution, increasing Se binding energy.
• Co-adsorption of Se and O leads to charge transfer from Ru on flat facets, but complex valence charge redistribution on low-coordinated sites.
• Se modification weakens O bonding to Ru particles, yet overall O binding energies on nanoparticles are higher than on Se/Ru(0001) surfaces.

Conclusions:

• The high reactivity observed in Se/Ru nanoparticles due to Se modification is unfavorable for ORR.
• Larger Ru nanoparticles with well-developed flat facets are expected to be more efficient ORR catalysts than smaller nanoparticles with many under-coordinated sites.