Pd-Pt alloy nanocrystals (NCs) with hollow structures such as nanocages with porous walls and dendritic hollow structures and Pd@Pt core-shell dendritic NCs could be selectively synthesized by a galvanic replacement method with uniform Pd octahedral and cubic NCs as sacrificial templates. Fine control over the degree of galvanic replacement of Pd with Pt allowed the production of Pd-Pt NCs with distinctly different morphologies. The synthesized hollow NCs exhibited considerably enhanced oxygen reduction activities compared to those of Pd@Pt core-shell NCs and a commercial Pt/C catalyst, and their electrocatalytic activities were highly dependent on their morphologies. The Pd-Pt nanocages prepared from octahedral Pd NC templates exhibited the largest improvement in catalytic performance. We expect that the present work will provide a promising strategy for the development of efficient oxygen reduction electrocatalysts and can also be extended to the preparation of other hybrid or hetero-nanostructures with desirable morphologies and functions.

The many faces of noble metals: Through the simultaneous reduction of Au and Pd ions in the presence of octahedral Au nanocrystal (NC) seeds, hexoctahedron‐like convex Au@Pd core–shell NCs, enclosed predominantly by high‐index {12 5 3} facets, were synthesized under aqueous room‐temperature conditions (see picture). The convex Au@Pd NCs showed much higher electrocatalytic properties toward ethanol oxidation than other types of Au@Pd NCs.

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Au-Pd alloy nanocrystals (NCs) with a hexoctahedral structure, enclosed exclusively by high-index {541} facets, are prepared via the simultaneous reduction of Au and Pd precursors without added seeds or additional metal ions as structure-regulating agents. Manipulating the NC growth kinetics via control of the relative amount of reductant is the key synthetic lever for controlling the morphology of the Au-Pd NCs. The hexoctahedral Au-Pd NCs exhibit higher catalytic performance toward the electro-oxidation of ethanol than low-index-faceted Au-Pd NCs.

Single-crystalline gold nanoplates with a thick- ness of less than 100 nm were synthesized by the reduction of HAuCl4 in water with cetyltrimethylammonium chloride, and their structures were confirmed by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction measurements. The formation and surface structures of octanethiol (OT) self-assembled monolayers (SAMs) on gold nanoplates were examined by means of atomic force microscopy and scanning tunnelling microscopy (STM). Molecularly resolved STM observation showed that OT SAMs on gold nanoplates at 25 °C for 24 h were composed of two mixed phases containing well-ordered (√3 × √3)R30° and c(4 × 2) domains and disordered domains, which are comparable to the formation of fully covered (√3 × √3)R30° or c(4 × 2) structures on conventional Au(111) films. After thermal annealing of the precovered OT SAMs on gold nanoplates at 70 °C for 30 min, we clearly observed the structural transitions of OT SAMs from the two mixed phases to the loosely packed, uniform 6 × √3 phase, which is mainly driven by the optimization of van der Waals interactions between alkyl chains via the rearrangement of OT molecules in the two mixed domains to reach thermodynamically stable SAMs. Our results herein provide new insights into the formation and structural behaviors of alkanethiol SAMs on size-confined gold nanostructures.