Wet-Chemical Synthesis of Concave Hexoctahedral Pd and Pd@Pt Nanocrystals for Methanol Electrooxidation.

Nanocrystals (NCs) exposed with high-index facets usually show enhanced electrocatalytic performances. However, it is a great challenge to persevere with high-index facets against their high surface energy during the synthesis. Herein, we successfully synthesize concave hexoctahedral (c-HOH) Pd NCs exposed with 48 high-index {741} facets using a facile one-pot wet-chemical protocol. Control experiments illustrate that l-ascorbic acid plays a critical role in the formation of the c-HOH morphology, acting as both reducing and capping agents. Moreover, we can extend the synthesis for fabricating c-HOH Pd@Pt core-shell NCs by simply introducing a Pt precursor into the reaction solution, attaining remarkably boosted electrocatalysis for methanol electrooxidation reaction (MOR). Integrating the merits of {741} facets, concave structure, and ligand and strain effect of the core-shell structure, c-HOH Pd@Pt core-shell NCs showed an excellent MOR mass activity of 1.18 A mg or 3.60 A mg, which is 3.80 or 11.61 times higher than that of commercial Pt/C, respectively.