Scientists at the University of Delaware may have developed a polymer for use in a fuel cell that has high conductivity but also does not swell, thereby 
avoiding a common problem with similar cells that have problems with mechanical integrity.
The membrane, says the developer, Yushan Yan, distinguished professor of engineering at the university, is a game-changing development that promises to revolutionize the way engineers think about traditional chemical crosslinking methods used to create strong fuel cell membranes. Until now, polymer membranes had to be strong and resistant to water swelling. To have that strength, however, polymer chains were traditionally chemically crosslinked. The catch was that chemical crosslinking hampered the membranes’ other functionalities, according to the University of Delaware announcement about Yan’s development.
Yan’s research team demonstrated that it is possible to create polymer bonds that are as effective as those that are chemically crosslinked, without the brittleness crosslinked polymers typically display. The announcement describes Yan’s innovation:
Yan explains that traditionally when engineers want to increase conductivity in a polymer, they increase the density of the ionic groups present in the polymer. However, with the high density comes membrane swelling, which can destroy the mechanical integrity of the polymer and reduce or eliminate its usefulness. By exploiting the fact that positive and negatively charged ions physically attract one another, Yan’s group was able to increase the strength of the polymer bond without any chemical crosslinking.
Yan took advantage of the van der Waals interaction, a group of weak molecular interactions. “We realized that we can play with the van der Waals interaction between the polymer chains, because a positive charge complemented by a negative charge creates what’s called a ‘dipole moment’ that polarizes the molecules and causes them to attract; and the larger the dipole moment, the stronger the interaction,” he says.
The team then designed the polymer chain to have high electron density and therefore be more influenced by the van der Waal interaction, increasing the attractive force without creating any chemical bond. “It is a bond that is created by the presence and strength of these positive and negative charges,” Yan says.
The discovery of leveraging the van der Waal force was an accident that occurred while experimenting with new polymers. “We suddenly realized that the membrane wasn’t swelling anymore, but conductivity remained high,” Yan says.
The development would reduce costs for manufacturing fuel cells, Yan says, allowing the technology to become more competitive with conventional technology that often uses expensive platinum. Yan sees the technology as one that can replicate the conventional lifespan of a vehicle’s internal combustion engine.
Source: “Opposites attract,” University of Delaware press release, 6/29/12
Image by Kathy F. Atkinson, University of Delaware, used with permission.
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.
