Palladium@Platinum Concave Nanocubes with Enhanced Catalytic Activity toward Oxygen Reduction

We report the facile synthesis of Pd@Pt core-shell nanocubes with concave facets on the surface and their enhanced activities toward the oxygen reduction reaction. The success of this synthesis depends critically on our ability to manipulate both the deposition rate of atoms and the surface diffusion rate of the adatoms. In the first step, Pd nanocubes with side faces capped by Br- ions are transformed into concave nanocubes by seed-mediated growth. The PdCl42- precursor is added in one shot, and the growth is conducted at 40 degrees C to accelerate deposition and decelerate surface diffusion. For the synthesis of Pd@Pt core-shell concave nanocubes, the PtCl42- precursor is added dropwise into a suspension of the Pd concave nanocubes and reduced by citric acid at 90 degrees C. As such, we can deposit an ultrathin Pt shell on the surface of each Pd concave nanocube. Despite their much larger size, the Pd@Pt concave nanocubes exhibit greater specific electrochemical surface areas than a commercial Pt/C catalyst, which implies the more efficient dispersion of Pt atoms on the surface. In addition to excellent durability, the catalyst based on Pd@Pt concave nanocubes shows enhanced catalytic activities toward the oxygen reduction reaction.