Underpotential Deposition-Mediated Layer-by-Layer Growth of Thin Films

Brookhaven National Laboratory

Increase in catalytic activity for the oxygen reduction reaction (ORR) after coating palladium-on-carbon catalysts with four monolayers of platinum by underpotential deposition.

Technology Marketing Summary

Platinum is a very good, albeit expensive, electrocatalyst. In order to increase the catalytic activity of an electrocatalyst per mass of noble metal (the mass activity), nanoparticles of less expensive materials are coated with atomically thin layers of platinum. First a monolayer of a sacrificial base metal such as copper or lead is deposited onto a core particle via underpotential deposition. Then the base metal is replaced by galvanic displacement with the catalytically active more noble metal. The coated composite can be used as an electrocatalyst in place of pure platinum, for example, in fuel cells.

Description

This invention utilizes copper underpotential deposition (UPD) potential cycles to enhance the interlayer diffusion rate during a diffusion-controlled overpotential deposition of platinum on palladium nanoparticles, for example. The deposition starts at the potential near Cu bulk deposition where a full monolayer Cu covers the Pd surface. As the Cu monolayer is partially stripped in the positive potential sweep, Pt is deposited under diffusion control. When the potential sweep turns in negative direction, Cu UPD covers the deposited Pt preventing multiplayer growth before the completion of the first Pt layer. The role of Cu deposition/stripping is (1) to slow down Pt deposition rate and to enhance the Pt interlayer diffusion rate so that added Pt atoms in each potential cycle can settle down at the most energetically favored sites, which leads to layer by layer growth; (2) the current response to the potential cycles serves as an in situ monitor for the deposition processes.

Benefits

This method allows deposition of smooth, atomically thin layers of noble metal catalysts, reducing the amount of precious metal used and so the cost of the catalysts.

Applications and Industries

Fuel cell catalysts; oxygen-reduction; heterogeneous catalysis

More Information

Wang, et al., “Overpotential deposition of Ag monolayer and bilayer on Au(1 1 1) mediated by Pb adlayer underpotential deposition/stripping cycles,” Surf. Sci., 540, 230-236 (2003). DOI: 10.1016/S0039-6028(03)00792-1

Technology Status

Technology ID	Development Stage	Availability	Published	Last Updated
BSA 08-27	Prototype	Available	04/22/2011	04/22/2011

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To:	Kimberley Elcess<elcess@bnl.gov>
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