Computational Design of Core/Shell Nanoparticles for Oxygen Reduction Reactions.

A computational strategy to design core/shell nanoparticle catalysts for oxygen reduction reactions (ORRs) is proposed based on multiscale modeling. Using a quantum mechanics/molecular mechanics (QM/MM) coupling method, we have studied the ORR on Pt-Cu core/shell nanoparticles with the size ranging from 3 to 8 nm. We have calculated the oxygen adsorption energy on the nanoparticle surface (a descriptor for ORR activity) as a function of the nanoparticle size and thickness of the Pt shell. We find that the Pt-Cu core/shell nanoparticles exhibit higher ORR activities than flat Pt(111) surfaces, consistent with experimental observations. We predict that the diameter of the core/shell nanoparticles should be larger than 7 nm to reach the peak of ORR activities. By examining the effects of ligand, quantum confinement, and surface strain, we confirm that the strain plays the dominant role on ORR activities for the core/shell nanoparticles. A universal relation between the surface strain and the oxygen adsorption energy is established based on which one can computationally screen and design core/shell nanoparticle catalysts for superior ORR activities.