Gold-platinum nanoparticles: Alloying and phase segregation

The ability to control nanoscale alloying and phase segregation properties is important for the exploration of multimetallic nanoparticles for the design of advanced functional materials and catalysts. This report highlights recent insights into the nanoscale phase properties of gold-platinum (AuPt) nanoparticles, which serves as an example to shine a light on the importance of changes in physical and chemical properties in which nanoscale multimetallic materials may differ from their bulk counterparts. In contrast to the wide miscibility gap well known for the bulk gold-platinum system, the bimetallic nanoparticles have been demonstrated to exist in phases ranging from alloy, partial alloy, to phase segregation depending on the preparation conditions, the bimetallic composition, and the supporting materials. For AuPt nanoparticles supported on carbon materials, the nanoscale alloying or phase segregation is shown to be controllable by thermal treatment temperatures, which is not only evidenced by detailed analysis of the phase and surface properties, but also supported by theoretical modeling based on thermodynamic and density function theory. The understanding of the nanoscale phase properties can be correlated with the electrocatalytic activities for fuel cell reactions such as methanol oxidation reaction and oxygen reduction reaction. Implications of the new insights to designing and nanoengineering the phase properties of multimetallic nanoparticles and catalysts are also briefly discussed.