Synthesis of single crystalline Ru@Pt core-shell nanoparticles
Fabricating subnanometre-thick core-shell nanocatalysts is effective for obtaining high surface area of an active metal with tunable properties. The key to fully realize the potential of This approach is a reliable synthesis method to produce atomically ordered core-shell nanoparticles. Here we report new insights on eliminating lattice defects in core-shell syntheses and opportunities opened for achieving superior catalytic performance. Ordered structural transition from ruthenium hcp to platinum fcc stacking sequence at the core-shell interface is achieved via a green synthesis method, and is verified by X-ray diffraction and electron microscopy techniques coupled with density functional theory calculations. The single crystalline Ru cores with well-defined Pt bilayer shells resolve the dilemma in using a dissolution-prone metal, such as ruthenium, for alleviating the deactivating effect of carbon monoxide, opening the door for commercialization of low-temperature fuel cells that can use inexpensive reformates (H2 with CO impurity) as the fuel.
Atomic resolution STEM (CFN) shows crystalline order for Pt shell (red dots) on Ru core nanocrystals (blue dots).
We developed a scalable green-synthesis method that produces single crystalline Ru@Pt nanoparticles with uniform Pt shell 1 to 3 atomic layers thick. Ru cores were found disordered in previously synthesized Ru@Pt core-shell nanoparticles based on much weakened Ru XRD intensities. In the absence of surfactant and metal template, we synthesized Ru cores with narrow particle size distribution and coated them with a uniform Pt shell using solvent ethanol as the reductant via fine tuning its reducing power. Via in-depth structural analysis coupled with DFT calculations, we identified the cause as defect-induced partial alloying, which resulted in smaller Ru cores with thicker Pt-rich shells. By minimizing the defects in the Ru cores and fine-tuning the conditions for Pt coating, we avoided partial alloying and demonstrated an ordered hcp-fcc phase transition at the Ru-Pt core-shell interface. Attaining a sharp, uniform core-shell interface is crucial for optimizing activity via tuning Pt-shell thickness and for protecting the Ru core from dissolution at high potentials.
Nature Comm. 2013 DOI: 10.1038/ncomms3466
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Last Modified: October 25, 2013