One-pot synthesis of Pd@Pt core–shell nanocrystals for electrocatalysis: control of crystal morphology with polyoxometalate

Abstract

Pt-based bimetallic nanocrystals (NCs) are an important class of catalytic materials especially in the area of energy conversion due to their outstanding catalytic performance. The catalytic function of Pt-based bimetallic NCs toward a specific catalysis reaction can be optimized by tailoring their surface structure, which can be realized through the precise control of the NC morphology. In the present work, we developed a facile one-pot polyoxometalate (POM)-mediated synthesis approach for the synthesis of Pt-based bimetallic NCs with controlled morphologies and fine crystal structures, and investigated the influence of their morphology on their catalytic function. Pd@Pt core–shell NCs with well-defined morphologies and controlled surface structures could be prepared by the simultaneous reduction of Pt and Pd precursors in the presence of a typical Keggin-type POM (H₃PMo₁₂O₄₀) and ascorbic acid (AA). During the formation of NCs, the POMs served not only as a stabilizing agent but also a reducing agent. Notably, the presence of the POMs as well as the relative concentration of AA to metal precursors could afford fine control over the growth mode of the Pt shells on the Pd cores, and thus the final morphology of the Pd@Pt NCs. The prepared POM-passivated Pd@Pt NCs outperformed Pd@Pt NCs synthesized without the POMs as well as a commercial Pt/C catalyst for the electrooxidation of methanol, and their catalytic activity and stability distinctly depended on their Pt shell structure. We envision that this strategy will pave the way for the rational design of NC-based catalyst systems.