One-Pot Synthesis of Pd@Pt_nL Core-Shell Icosahedral Nanocrystals in High Throughput through a Quantitative Analysis...

The rational design and implementation of a one-pot method is reported for the facile synthesis of Pd@Pt_nL (nL denotes the number of Pt atomic layers) core-shell icosahedral nanocrystals in a single step. The success of this method relies on the use of Na₂ PdCl₄ and Pt(acac)₂ as the precursors to Pd and Pt atoms, respectively. Our quantitative analysis of the reduction kinetics indicates that the Pd^II and Pt^II precursors are sequentially reduced with a major gap between the two events. Specifically, the Pd^II precursor is reduced first, leading to the formation of Pd-based icosahedral seeds with a multiply-twinned structure. In contrast, the Pt^II precursor prefers to take a surface reduction pathway on the just-formed icosahedral seeds. As such, the otherwise extremely slow reduction of the Pt^II precursor can be dramatically accelerated through an autocatalytic process for the deposition of Pt atoms as a conformal shell on each Pd icosahedral core. Compared to the conventional approach of seed-mediated growth, the throughput for the one-pot synthesis of Pd@Pt_nL core-shell nanocrystals can be increased by more than 30-fold. When used as catalysts, the Pd@Pt_4.5L core-shell icosahedral nanocrystals show specific and mass activities of 0.83 mA cm^-2 and 0.39 A mg_Pt ^-1 , respectively, at 0.9 V toward oxygen reduction. The Pt-based nanocages derived from the core-shell nanocrystals also show enhanced specific (1.45 mA cm^-2 ) and mass activities (0.75 A mg_Pt ^-1 ) at 0.9 V, which are 3.8 and 3.3 times greater than those of the commercial Pt/C, respectively.