A Mechanistic Study on the Nucleation and Growth of Au on Pd Seeds with a Cubic or Octahedral Shape

This article reports a systematic study on the seed-mediated growth of Pd-Au bimetallic nanocrystals with a variety of controlled morphologies. The key to the success of this synthesis is to manipulate the reaction kinetics by controlling a set of experimental parameters, which include the amount of ascorbic acid used as a reductant, the amount of HAuCl ₄ as a precursor to elemental Au, the reaction temperature, and the type of seeds employed. Starting from Pd nanocubes of 18nm in edge length, Pd-Au bimetallic nanocrystals with a number of morphologies, which includes hybrid dimers, core-shell nanocubes with flat faces, and core-shell nanocubes with concave faces could all be obtained by simply speeding up the reduction of HAuCl ₄. The same synthesis and control could also be extended to seeds based on Pd octahedrons. For the first time, it was possible to generate Pd@Au core-shell nanocubes and octahedrons with concave faces. The Pd@Au core-shell nanocubes with concave faces exhibited enhanced activity in catalyzing the oxidization of ascorbic acid relative to their counterparts with flat faces or the cubic Pd seeds.