A Pathway for the Growth of Core−Shell Pt−Pd Nanoparticles

The aging of both Pt−Pd nanoparticles and core− shell Pt−Pd nanoparticles has been reported to result in alloying of Pt with Pd. In comparison to monometallic Pt catalysts, the growth of Pd−Pt bimetallics is slower; however, the mechanism of growth of particles and the mechanism by which Pd improves the hydrothermal durability of bimetallic Pd−Pt particles remains uncertain. In our work on hydrothermal aging of core−shell Pt−Pd nanoparticles, synthesized by solution methods, with varying Pd:Pt ratio of 1:4, 1:1, and 4:1, we compare the growth of core−shell Pt− Pd nanoparticles and find that particles grow by migrating and joining together. The unique feature of the observed growth is that Pd shells from both particles open up and join, thereby allowing the cores to merge. At high temperatures, alloying occurs in good agreement with reports by other workers.