Facile syntheses and enhanced electrocatalytic activities of Pt nanocrystals with {hkk} high-index surfaces

Platinum (Pt) is an outstanding catalyst for many important industrial products. Because of its high cost and scarce reserves, it is very important to improve the performance of Pt catalysts. As the metal nanocrystals (NCs) with high-index surfaces usually show very good catalytic activity because of their high density of atomic steps and kinks, the preparation of Pt NCs with high-index facets has become a very important and hot research topic recently. In this article, we report a facile synthesis of high-yield Pt NCs with a series of {hkk} high-index facets including {211} and {411} via a solvothermal method using Pt(II) acetylacetonate as the Pt source, 1-octylamine as the solvent and capping agent, and formaldehyde as an additional surface structure regulator. Multipod Pt NCs with dominant {211} side surfaces were produced without formaldehyde, while concave Pt NCs with dominant {411} surfaces formed under the influence of formaldehyde. By analyzing the products by IR spectroscopy, we found the presence of CO on the surface of concave Pt NCs with {411} surfaces prepared from the solution containing formaldehyde. It was concluded that amine mainly stabilized the monoatomic step edges, resulting in the {211} exposed surface; with addition of formaldehyde, it decomposed into CO, leading to the formation of {411} surfaces by the additional adsorption of the CO on the {100} terraces. In addition, it was found that the as-prepared Pt NCs with high-index {211} and {411} surfaces exhibited much better catalytic activity in the electro-oxidation of ethanol than a commercial Pt/C catalyst or Pt nanocubes with low-index {100} surfaces, and the catalytic activities of Pt crystal facets decreased in the sequence {411}>{211}>{100}.