[Editors] MIT: First atomic–scale images of fuel-cell nanoparticles

[Teresa Herbert]

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MIT: First atomic–scale compositional images of fuel-cell nanoparticles
--Better understanding of particles could lead to better compositions
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For Immediate Release
THURSDAY, OCT. 2, 2008

Contact: Teresa Herbert, MIT News Office
E: therbert at mit.edu, T: 617-258-5403

Photo Available


CAMBRIDGE, Mass. -- In a step toward developing better fuel cells for  
electric cars and more, engineers at MIT and two other institutions  
have taken the first images of individual atoms on and near the  
surface of nanoparticles key to the eco-friendly energy storage devices.

Nanoparticles made of platinum and cobalt are known to catalyze some  
of the chemical reactions behind fuel cells, making those reactions  
run up to four times faster than if platinum alone is used as the  
catalyst.

No one, however, understands exactly why. That’s because “little is  
known about the nanoparticles’ surface atomic structure and  
chemistry,” which are key to the particles’ activity, said Yang Shao- 
Horn, an associate professor in the Department of Mechanical  
Engineering and Department of Materials Science and Engineering and  
director of the Electrochemical Energy Laboratory at MIT.

Using a new technique known as aberration-corrected Scanning  
Transmission Electron Microscopy, Shao-Horn’s team, in collaboration  
with Professor Paulo Ferreira of the University of Texas at Austin and  
Dr. Larry Allard of Oak Ridge National Laboratory, identified specific  
atomic structures near the surface of such a catalyst. That  
information in hand, the researchers propose a theory for why the  
material is so active. Perhaps most importantly, “knowing the surface  
composition will help us design even better catalysts,” Shao-Horn said.

The work was reported in the Sept. 24 online issue of the Journal of  
the American Chemical Society.

The researchers analyzed platinum and cobalt nanoparticles that were  
either treated with acid, or treated with acid then subjected to high  
heat. Nanoparticles produced both ways are known to be more active  
than platinum alone. Shao-Horn and colleagues found that each, in  
turn, also had slightly different surface structures.

For example, in the nanoparticles subjected to heat treatments, the  
platinum and cobalt atoms formed a “sandwich-like” structure. Platinum  
atoms covered most of the surface, while the next layer down was  
composed primarily of cobalt. Successive layers contained mixtures of  
the two.

The team proposes that these particular nanoparticles are up to four  
times more active than platinum alone because the platinum atoms on  
the surface are constrained by the cobalt atoms underneath. “This  
modifies the interatomic distances between the platinum atoms on the  
nanoparticle surface,” making them more effective in chemical  
reactions key to fuel cells, Shao-Horn said.

She further noted that “this work bridges the gap between our  
understanding of electrocatalysis in bulk materials and at the nano- 
scale.”

In addition to Shao-Horn, Allard, and Ferreira, who is also an MIT  
research affiliate, other members of the research team are Shuo Chen,  
first author of the paper and a postdoctoral associate in mechanical  
engineering; Wenchao Sheng, a graduate student in chemistry; and  
Naoaki Yabuuchi, a research affiliate in mechanical engineering.

The Department of Energy and the National Science Foundation, through  
its Materials Research Science and Engineering Center program, funded  
the work.

By Elizabeth Thomson, MIT News Office

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