MIT creates improved material for fuel cells with lower
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 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 is that the 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 exploring if 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 his colleagues have begun exploring the new
material’s potential use in photovoltaics. That work is funded by the
MIT Energy Initiative. For more information, please visit http://web.mit.edu/mitei.