Study identifies path to design stable, durable polymer membranes for clean energy

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Electrolytes that convert chemical to electrical energy underlie the search for new power sources with zero emissions. Among these new power sources are fuel cells that produce electricity.

Fuel cells are often heavy, which is a problem because lighter power sources enable more energy-efficient fuel cell-powered vehicles. Therefore, scientists have been hard at work designing lightweight electrolytes—such as polymers that form electrolytic membranes—that are stable under the conditions in which electricity is generated.

By studying a model system using a combination of neutron scattering and computational models, the team of researchers from the Department of Energy's Oak Ridge National Laboratory and Sandia National Laboratories and Clemson University discovered a way to control the structure of polymeric electrolyte membranes. These findings, published in Macromolecules, could enhance the efficiency and longevity of clean energy–generating devices.

"Within these membranes, ions form clusters that allow the transport of the protons," said Lilin He, a neutron scattering scientist at ORNL and instrument scientist at the lab's High Flux Isotope Reactor (HFIR). "Better understanding the changes that occur in these clusters as they are exposed to solvents will help the development of optimized materials for better clean energy solutions."

The team found that when they added ethanol, a solvent and a potential fuel for clean energy generation, they could manipulate the ionic clusters, thus controlling the conductivity and mechanical properties of the polymers.

"With common solvents, we essentially control the formation of ionic clusters," said Dvora Perahia, a professor of chemistry and physics at Clemson University. "The ability to form controlled size and shape clusters is a key to designing effective lightweight membrane electrolytes for clean energy applications, with neutron scattering being crucial to determining the behavior of these clusters."

The unique properties of neutrons allow researchers to identify the changes that occur while electricity is generated as protons and water diffuse across these membranes. Researchers come from all over the world to use neutrons produced at HFIR to better understand materials such as polymeric electrolyte membranes. HFIR provides a steady-state neutron beam and is the strongest reactor-based neutron source in the U.S.

To obtain their results, the team combined small-angle neutron scattering at HFIR on the GP-SANS instrument with computational studies performed at the National Energy Research Scientific Computing Center (NERSC), located at Lawrence Berkeley National Laboratory.

These computations allowed the team to visualize how ethanol changes the ionic clusters. The computations helped determine that the alcohol molecules wrapped around the ions and opened the clusters just enough to allow the material to organize in a more stable way.

"When we can measure any property of materials in computations and then compare the results to those obtained from neutron scattering, it gives us confidence that the simulations are correct and can be used to understand the small-scale atomic details that enable predicting properties of new materials," said Gary S. Grest, a computational physicist at the Center of Integrated Nanotechnologies at Sandia National Laboratories.

More information: Chathurika Kosgallana et al, Clustering Effects on the Structure of Ionomer Solutions: A Combined SANS and Simulations Study, Macromolecules (2024). DOI: 10.1021/acs.macromol.3c01646

Provided by Oak Ridge National Laboratory