Two Developments in DMFC Output: New MIT Membrane Boosts Power More Than 50% and Sharp Achieves Highest Power Density Yet
MIT engineers have developed an alternative membrane for direct methanol fuel cells (DMFC) that can increase power output by more than 50%. The new material is also considerably less expensive than its conventional industrial counterpart, among other advantages.
Separately, Sharp Corporation announced that it achieved the world’s highest power density for direct methanol fuel cells (DMFC) for mobile equipment to date—0.3W/cc, or about 7 times greater than previous Sharp technology. This new technology would enable efficient power generation from a small cell volume making it possible to develop fuel cells that have almost the same volume but a longer continuous-use lifespan than lithium-ion batteries in use in mobile equipment.
MIT. The MIT work was reported in a recent issue of Advanced Materials by Paula T. Hammond, Bayer Professor of Chemical Engineering and leader of the research team, Avni A. Argun and J. Nathan Ashcraft. Argun is a postdoctoral associate in chemical engineering; Ashcraft is a graduate student in the same department.
“Our goal is to replace traditional fuel-cell membranes with these cost-effective, highly tunable and better-performing materials,” said. She noted that the new material also has potential for use in other electrochemical systems such as batteries.
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, especially for portable devices, because methanol has a high energy density, and the only waste products are water and carbon dioxide (the latter produced in small quantities).
The material currently used for the electrolyte in DMFC’s is expensive and 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.
Using a 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.
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%. 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.
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.
Sharp. Sharp developed a three-dimensional highly integrated stack structure through the use of thin cells made by microfabrication. This structure can be created by the alternate lamination of reed-shaped thin cells arranged in parallel at fixed intervals and reed-shaped (porous) spacers, with the cells and spacers running perpendicular to each other like a grid. With this structure, uniform and continuous spaces are secured, making it possible to increase the cell surface area per unit volume and smoothly circulate the air that is one of the sources for power generation.
In the future, through continuing to pursue the development of this elemental technology, cell volume can be further miniaturized, and the creation of cells with the same volume but a longer lifespan than the currently mainstream lithium-ion batteries can be achieved, according to Sharp.
Avni A. Argun, J. Nathan Ashcraft, Paula T. Hammond (2008) Highly Conductive, Methanol Resistant Polyelectrolyte Multilayers. Advanced Materials Vol. 20, No. 8, pp 1539-1543 doi: 10.1002/adma.200703205