[Editors] MIT creates new material for fuel cells

[Elizabeth Thomson]

For Immediate Release
THURSDAY, MAY 15, 2008
Contact: Elizabeth A. Thomson, MIT News Office -- Phone: 617-258-5402  
-- Email: thomson at mit.edu

PHOTOS, VIDEO AVAILABLE

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MIT creates new material for fuel cells

--Increases power output by more than 50 percent

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CAMBRIDGE, Mass.--MIT engineers have improved the power output of one  
type of fuel cell by more than 50 percent through technology that  
could help these environmentally friendly energy storage devices find  
a much broader market, particularly in portable electronics.

The new material key to the work is also considerably less expensive  
than its conventional industrial counterpart, among other advantages.

“Our goal is to replace traditional fuel-cell membranes with these  
cost-effective, highly tunable and better-performing materials,” said  
Paula T. Hammond, Bayer Professor of Chemical Engineering and leader  
of the research team. She noted that the new material also has  
potential for use in other electrochemical systems such as batteries.

The work was reported in a recent issue of Advanced Materials by  
Hammond, Avni A. Argun and J. Nathan Ashcraft. Argun is a  
postdoctoral associate in chemical engineering; Ashcraft is a  
graduate student in the same department.

Like a battery, a fuel cell has three principal parts: two electrodes  
(a cathode and anode) separated by an electrolyte. Chemical reactions  
at the electrodes produce an electronic current that can be made to  
flow through an appliance connected to the battery or fuel cell. The  
principal difference between the two? Fuel cells get their energy  
from an external source of hydrogen fuel, while conventional  
batteries draw from a finite source in a contained system.

The MIT team focused on direct methanol fuel cells (DMFCs), in which  
the methanol is directly used as the fuel and reforming of alcohol  
down to hydrogen is not required. Such a fuel cell is attractive  
because the only waste products are water and carbon dioxide (the  
latter produced in small quantities). Also, because methanol is a  
liquid, it is easier to store and transport than hydrogen gas, and is  
safer (it won't explode). Methanol also has a high energy density-a  
little goes a long way, making it especially interesting for portable  
devices.

The DMFCs currently on the market, however, have limitations. For  
example, the material currently used for the electrolyte sandwiched  
between the electrodes is expensive. Even more important: that  
material, known as Nafion, is permeable to methanol, allowing some of  
the fuel to seep across the center of the fuel cell. Among other  
disadvantages, this wastes fuel-and lowers the efficiency of the cell- 
because the fuel isn't available for the reactions that generate  
electricity.

Using a relatively new technique known as layer-by-layer assembly,  
the MIT researchers created an alternative to Nafion. “We were able  
to tune the structure of [our] film a few nanometers at a time,”  
Hammond said, getting around some of the problems associated with  
other approaches. The result is a thin film that is two orders of  
magnitude less permeable to methanol but compares favorably to Nafion  
in proton conductivity.

To test their creation, the engineers coated a Nafion membrane with  
the new film and incorporated the whole into a direct methanol fuel  
cell. The result was an increase in power output of more than 50  
percent.

The team is now exploring whether the new film could be used by  
itself, completely replacing Nafion. To that end, they have been  
generating thin films that stand alone, with a consistency much like  
plastic wrap.

This work was supported by the DuPont-MIT Alliance through 2007. It  
is currently supported by the National Science Foundation.

In addition, Hammond and colleagues have begun exploring the new  
material's potential use in photovoltaics. That work is funded by the  
MIT Energy Initiative. This Institute-wide initiative includes  
research, education, campus energy management and outreach  
activities, an interdisciplinary approach that covers all areas of  
energy supply and demand, security and environmental impact. For more  
information, please visit http://web.mit.edu/mitei/.

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Written by Elizabeth Thomson, MIT News Office