Water‐Based Synthesis of Sub‐10 nm Pt Octahedra and Their Performance towards the Oxygen Reduction Reaction

Abstract We report a facile, aqueous‐phase synthesis of sub‐10 nm Pt octahedral nanocrystals. The success of this synthesis relies on the use of poly(vinyl pyrrolidone) (PVP) as a mediator. By tracking the evolution of the Pt nanocrystals throughout the growth process, we found that single‐crystal seeds with a pseudo‐spherical shape are formed in the early stage of the synthesis, followed by growth through the preferential deposition of Pt atoms onto the {100} facets, directing the seeds to evolve into octahedra enclosed by {111} facets. We have manipulated the atom deposition rates by tuning various experimental parameters in an effort to support the mechanism for the formation of Pt octahedra. In addition, we have investigated the catalytic activity of these Pt nanocrystals towards oxygen reduction. For the 9‐nm Pt octahedra enclosed by {111} facets, they show a specific activity of 1.5 mA cm −2 , much greater than that of Pt nanocubes enclosed by {100} facets, which only has a specific activity of 0.28 mA cm −2 .