From EMSL: “Scarcity Drives Efficiency”

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September 28, 2015 [This just became available.]
Tim Scheibe tim.scheibe@pnnl.gov at EMSL
Younan Xia younan.xia@bme.gatech.edu

Platinum can be an efficient fuel cell catalyst

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Researchers developed a new class of catalysts by putting essentially all of the platinum atoms on the surface material and minimized the use of atoms in the core, thereby increasing the utilization efficiency of precious metals for fuel cells.

The Science

Platinum is an excellent catalyst for reactions in fuel cells, but its scarcity and cost have driven scientists to look for more efficient ways to use the precious metal. In a recent study, researchers developed a new class of catalysts by putting essentially all of the platinum atoms on the surface and minimizing the use of atoms in the core, thereby increasing efficient utilization of platinum for fuel cells.

The Impact

The novel nanocage catalyst will help promote the sustainable use of platinum and other precious metals for energy and other industrial applications. The reduced costs associated with the novel nanostructures will encourage commercialization of this technology for the development of zero-emission energy sources.

Summary

Researchers from Georgia Institute of Technology and Emory University, Xiamen University, University of Wisconsin–Madison, Oak Ridge National Laboratory and Arizona State University fabricated cubic and octahedral nanocages by depositing a few atomic layers of platinum on palladium nanocrystals, and then completely etching away the palladium core. Density functional theory (DFT) calculations suggested the etching process was initiated by the formation of vacancies through the removal of palladium atoms incorporated into the outermost layer during the deposition of platinum. Some of the computational work was performed using computer resources at EMSL, the Environmental Molecular Sciences Laboratory, a Department of Energy Office of Biological and Environmental Research user facility. DFT calculations were performed at supercomputing centers at EMSL, Argonne National Laboratory and the National Energy Research Scientific Computing Center.

Based on the findings, researchers propose that during platinum deposition, some palladium atoms are incorporated into the outermost platinum layers. Upon contact with the etchant—an acid or corrosive chemical—the palladium atoms in the outermost layer of the platinum shell are oxidized to generate vacancies in the surface of the nanostructure. The underlying palladium atoms then diffuse to these vacancies and are continuously etched away, leaving behind atom-wide channels. Over time, the channels grow in size to allow direct corrosion of palladium from the core. This process leads to a nanocage with a few layers of platinum atoms in the shell and a hollow interior.

Compared to a commercial platinum/carbon catalyst, the nanocages showed enhanced catalytic activity and durability. The findings demonstrate it is possible to design fuel cell catalysts with efficient use of precious metals without sacrificing performance. Moreover, it is possible to tailor the arrangement of atoms or the surface structure of catalytic particles to optimize their catalytic performance for a specific type of chemical reaction. The researchers are testing these catalysts in fuel cell devices to determine how to further improve their design for clean energy applications.

See the full article here .

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