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Posted: Jun 21, 2011
Stretching improves efficiency of material used in batteries, fuel cells and water purification
(Nanowerk News) Researchers at Virginia Tech in Blacksburg, Va. recently found a way to improve electricity generating fuel cells, potentially making them more efficient, powerful and less expensive. Specifically, they discovered a way to speed up the flow and filtering of water or ions, which are necessary for fuel cells to operate.
Simply put, the researchers stretched Nafion, a polymer electrolyte membrane, or PEM, commonly used in fuel cells and increased the speed at which it selectively filters substances from ions and water.
This image illustrates how the channels in a polymer electrolyte membrane material change when you stretch it. On the left is an unstretched sample of the material. The middle sample has been stretched at a ratio of 2:1, while the sample on the right, which shows the most channel alignment, has been stretched at a ratio of 4:1. (Image: Dr. Jing Li and Prof. Louis Madsen of Virginia Tech)
The resulting process could be important to a number of energy and environment-related applications such as any of several industrial processes that involve filtering, including improving batteries in cars, water desalination and even the production of artificial muscles for robots.
"I got the idea for some of these experiments after I saw Bob Moore give a talk at the University of North Carolina about Nafion when I was a post-doc there working with liquid crystals," said Madsen, an assistant professor of physical, polymer and materials chemistry who led the study.
In order to improve PEMs, Madsen and Virginia Tech Chemistry Professor Robert Moore studied exactly how water moves through Nafion at the molecular level and measured how changes in the structure of the material affected water flow. They found stretching it caused channels in the PEM material to align in the direction of the stretch, allowing water to flow through faster.
This image shows water molecules (red and white) inside ionic nanochannels (blue). (Image: Dr. Jing Li and Prof. Louis Madsen of Virginia Tech)
"Stretching drastically influences the degree of alignment," said Madsen. "So the molecules move faster along the direction of the stretch, and in a very predictable way. These materials actually share some properties with liquid crystals--molecules that line up with each other and are used in every LCD television, projector and screen."
"This is a very clever approach which demonstrates the advantages of interdisciplinary materials research and which may offer important benefits to both energy technologies and sustainability of our natural resources," said Andy Lovinger, polymers program director in the National Science Foundation's Division of Materials Research, which funded the study.
Nafion was discovered in the 1960's and is made up of molecules that combine the non-stick and tough nature of Teflon with the conductive properties of an acid. It is one of many PEMs used to filter water and ions that the researchers say could benefit from the stretching process.