Ultrasmall (<2 nm) Au@Pt Nanostructures: Tuning the Surface Electronic States for Electrocatalysis.

The ability to tune the electronic properties of nanomaterials has played a major role in the development of sustainable energy technologies. Metallic nanocatalysts are at the forefront of these advances. Their unique properties become even more interesting when we can control the distribution of the electronic states in the nanostructure. Here, we provide a comprehensive evaluation of the electronic surface states in ultrasmall metallic nanostructures by combining experimental and theoretical methods. The developed strategy allows the controlled synthesis of bimetallic nanostructures in the core-shell configuration, dispensing of the use of any surfactant or stabilizing agents, which usually inactivate important surface phenomena. The synthesized ultrasmall Au@Pt nanoarchitecture (∼1.8 nm) presents an enhanced performance catalyzing the hydrogen evolution reaction. First-principles calculations of projected and space-resolved local density of states of Au55@Pt92 (core-shell), Au55Pt92 (alloy), and Pt147 nanoparticles show a prominent increase in the surface electronic states for the core-shell bimetallic nanomaterial. It arises from a more-effective charge transfer from gold to the surface platinum atoms in the core-shell configuration. In pure Pt147 or Au55Pt92 alloy nanoparticles, a great part of the electronic states near the Fermi level is buried in the core atoms, disabling these states for catalytic applications. The proposed experimental-theoretical approach may be useful for the design of other systems composed of metallic nanoparticles supported on distinct substrates, such as two-dimensional materials and porous matrices. These nanomaterials find several applications not only in heterogeneous catalysis but also in sensing and optoelectronic devices.

Engineering two-dimensional gold nanostructures using graphene oxide nanosheets as a template.

The rich plasmon resonance modes and local field enhancements of two-dimensional (2D) noble metal nanostructures have boosted their application in distinct areas like catalysis, photonics, medicine and sensing. Here, we develop a unique strategy for the controlled growth of asymmetric 2D gold nanostructures in aqueous media using graphene oxide as a template. By performing mild reduction of gold ions on the surface of Au seeds (∼2 nm) attached to graphene oxide nanosheets, the anisotropic growth of 2D gold nanostructures can be carried out through a simple procedure with a tunable control of the final size, shape and thickness, and consequently on their optical properties, without using surfactants.