Pt-Au alloying at the nanoscale

The formation of nanosized alloys between a pair of elements, which are largely immiscible in bulk, is examined in the archetypical case of Pt and Au. Element specific resonant high-energy X-ray diffraction experiments coupled to atomic pair distribution functions analysis and computer simulations prove the formation of Pt-Au alloys in particles less than 10 nm in size. In the alloys, Au-Au and Pt-Pt bond lengths differing in 0.1 Å are present leading to extra structural distortions as compared to pure Pt and Au particles. The alloys are found to be stable over a wide range of Pt-Au compositions and temperatures contrary to what current theory predicts. The alloy-type structure of Pt-Au nanoparticles comes along with a high catalytic activity for electrooxidation of methanol making an excellent example of the synergistic effect of alloying at the nanoscale on functional properties.