Advancement in heterogeneous catalysis relies on the capability of altering material structures at the nanoscale, and that is particularly important for the development of highly active electrocatalysts with uncompromised durability. Here, we report the design and synthesis of a Pt-bimetallic catalyst with multilayered Pt-skin surface, which shows superior electrocatalytic performance for the oxygen reduction reaction (ORR). This novel structure was first established on thin film extended surfaces with tailored composition profiles and then implemented in nanocatalysts by organic solution synthesis. Electrochemical studies for the ORR demonstrated that after prolonged exposure to reaction conditions, the Pt-bimetallic catalyst with multilayered Pt-skin surface exhibited an improvement factor of more than 1 order of magnitude in activity versus conventional Pt catalysts. The substantially enhanced catalytic activity and durability indicate great potential for improving the material properties by fine-tuning of the nanoscale architecture.

The development of electrocatalytic materials of enhanced activity and efficiency through careful manipulation, at the atomic scale, of the catalyst surface structure has long been a goal of electrochemists. To accomplish this ambitious objective, it would be necessary both to obtain a thorough understanding of the relationship between the atomic-level surface structure and the catalytic properties and to develop techniques to synthesize and stabilize desired active sites. In this contribution, we present a combined experimental and theoretical study in which we demonstrate how this approach can be used to develop novel, platinum-based electrocatalysts for the CO electrooxidation reaction in CO(g)-saturated solution; the catalysts show activities superior to any pure-metal catalysts previously known. We use a broad spectrum of electrochemical surface science techniques to synthesize and rigorously characterize the catalysts, which are composed of adisland-covered platinum surfaces, and we show that highly undercoordinated atoms on the adislands themselves are responsible for the remarkable activity of these materials.

LETTERfactor. 19 A hexagonal unit cell of a = b = 2.775 Å and c = 6.797 Å, where c-axis) Pt [111], was used in our measurements and analysis for convenience.' ASSOCIATED CONTENT b S Supporting Information. Details on the specular rod data and fitting as well as the resonance scattering data and fitting. This material is available free of charge via the Internet at http://pubs.acs.org.

Stability and dissolution of platinum single-crystal surfaces were investigated with atomic force microscopy and inductively coupled plasma mass spectrometry. Both low-index surfaces and nanofaceted surfaces were investigated. A clear difference was observed between the large low-index surfaces and the nanofaceted surfaces. In the low-index surfaces, the platinum oxide formation passivates the surfaces, resulting in a lower dissolution rates at higher potentials. The nanofaceted surface dissolves faster at a higher potential, indicating the edges and corners are the main sources of dissolution. The differences in the dissolution behaviors between the low-index surfaces, (111), (100), and (110), are also discussed.