Pt-Based Icosahedral Nanocages: Using a Combination of {111} Facets, Twin Defects, and Ultrathin Walls to Greatly Enhance Their Activity toward Oxygen Reduction

Engineering the surface structure of noble-metal nanocrystals offers an effective route to the development of catalysts or electrocatalysts with greatly enhanced activity. Here, we report the synthesis of Pt-based icosahedral nanocages whose surface is enclosed by both {111} facets and twin boundaries while the wall thickness can be made as thin as six atomic layers. The nanocages are derived from Pd@Pt_4.5L icosahedra by selectively etching away the Pd in the core. During etching, the multiply twinned structure can be fully retained whereas the Pt atoms in the wall reconstruct to eliminate the corrugated structure built in the original Pt shell. The Pt-based icosahedral nanocages show a specific activity of 3.50 mA cm^-2 toward the oxygen reduction reaction, much greater than those of the Pt-based octahedral nanocages (1.98 mA cm^-2) and a state-of-the-art commercial Pt/C catalyst (0.35 mA cm^-2). After 5000 cycles of accelerated durability test, the mass activity of the Pt-based icosahedral nanocages drops from 1.28 to 0.76 A mg^-1_Pt, which is still about four times greater than that of the original Pt/C catalyst (0.19 A mg^-1_Pt).