Synthesis and composition evolution of bimetallic Pd–Pt alloy nanoparticles

Abstract

This paper reports a study on the synthesis of Pd–Pt alloy nanoparticles and compositionevolution of the alloys. The synthesis involves Pd and Pt acetylacetonate as the metalprecursors and trioctylphosphine (TOP) as the solvent. Thermal decomposition of thePd–TOP complex resulted in Pd nanoparticles, while substitution of Pt in the Pt–TOPcomplex by Pd allowed formation of the Pd–Pt alloys. It was observed that thePd–Pt nanoparticles formed at the very beginning in the synthesis process are Pdrich with various nanoparticle sizes ranging from 1.5 to 25 nm in diameter. Thesenanoparticles averaged out through a digestive ripening process and reached a finalsize of 3.5 nm in about 10 min. The alloy compositions evolved throughout thesynthesis process and only reached the preset Pd to Pt ratio of the precursors in120 min. It was found that Pt acetylacetonate alone in TOP cannot produce Ptnanoparticles, which was attributed to the formation of a Pt–TOP complex and astrong coordination of Pt to the phosphine. This observation led us to proposean atomic exchange process between the Pt–TOP complex and the Pd atomsat the nanoparticle surface. As a result, the alloy formation process is limitedby a substitution and diffusion rate of the Pt atoms at the surface of the alloynanoparticles.