DFT-Computed Trends in the Properties of Bimetallic Precious Metal Nanoparticles with Core@Shell Segregation

Bimetallic precious metal nanoparticles (NPs) are promising as components of heterogeneous catalytic systems; however, the synergistic effects that occur when combining multiple elements in these discrete systems are still being understood. Here, we present a systematic computational study that investigates the effect of geometry and compositional arrangements on the properties of bimetallic core@shell precious metal NPs. Combinations of the elements Ag, Au, Pd, and Pt are considered, and for surface coverages of just one monolayer, we show that the electronic properties of the NPs, such as the Fermi energy and d-band center, are strongly correlated with the element that occupies sites on the NP surface, in qualitative but not quantitative agreement with previous two-dimensional slab calculations. By contrast, strain effects from structural choices and elemental size mismatch play a minor role in altering the energetic levels. Charge transfer between the core and shell regions of the NPs is a balance between the increased electronic degrees of freedom that exist at a NP surface and the relative electronegativity of the constituent elements. We use our results to rationalize recent experimental observations and we foresee that the outcomes will assist the rational atom by-atom design of future NP catalysts.