(304g) The Effects of Oxidation and Transition Metal-Doping on the Structure and Properties of Pt-Ni Nanoparticles

We present the use of ab-initio calculations and the cluster expansion method to build a direct bridge between atomic-scale structures and catalytic properties for Pt-Ni nanoparticles for the oxygen reduction reaction (ORR). Although the practical use of Pt-Ni catalysts is limited by Ni dissolution in operating conditions, it has been shown that it is possible to stabilize octahedral Pt–Ni nanoparticles by doping them with a small amount of Mo (around 1.6% mole fraction). Using a cluster expansion built on nanoparticles, we show that the combination of the stabilization of sites with low coordination (e.g. edge and vertex sites), and/or the reduction of equilibrium surface Ni composition due to Mo doping greatly stabilizes the shape and composition of Pt-Ni nanoparticles. Our calculations also reveal insights into the shape evolution of Pt–Ni nanoparticles: the preferential oxidation of edges can make (111) face sites more vulnerable to dissolution than edge sites, which may contribute to the observed formation of Pt-Ni nanoframes and nanoparticles with concave surfaces. To facilitate the rational design of Pt-Ni based nanoparticles with optimized structures for the ORR, we have extended our approach to model the oxygen binding energy on the surface of nanoparticles with experimentally observed sizes (~5nm), enabling the prediction of ORR current as a function of particle structure.