(240b) Computational Investigation of Transition Metal Alloying Effects on the Structure and Enhanced Stability of Pt-Ni Nanoparticles

We present the use of ab-initio calculations and the kinetic Monte Carlo method to calculate atomic-scale structures and properties for Pt-Ni nanoparticles, promising catalysts for the oxygen reduction reaction (ORR). Although the practical use of Pt-Ni catalysts is limited by Ni dissolution under cell operating conditions, it has recently been shown that it is possible to stabilize octahedral Pt–Ni nanoparticles by alloying them with transition metals (e.g. Mo, Cu, and Rh). We discuss two examples of alloyed Pt-Ni nanoparticles: Mo-Pt-Ni and Cu-Pt-Ni. Using a kinetic Monte Carlo (KMC) model based on cluster expansions, we demonstrate that Mo atoms are preferentially located on the vertex and edge sites of Mo-Pt-Ni in the form of oxides which are stable within the wide potential window of the electrochemical cycle. These surface Mo oxides help protect Ni in sub-surface layers against acid dissolution. KMC simulations reveal that the enhanced stability of Cu-Pt-Ni is likely due to the reduction of the number of Ni and Cu atoms on the surface during synthesis, reducing the opportunity for Ni and Cu atoms in sub-surface layers to move to the surface and dissolve. We demonstrate how our approach can be used to facilitate the rational design of nanocatalysts by predicting oxygen binding energy on the surface of Pt-Ni nanoparticles with experimentally observed sizes (~5nm), enabling the prediction of catalytic activity for the oxygen reduction reaction as a function of atomic-scale particle structure.