Researchers at the University of Chicago Pritzker School of Molecular Engineering (UChicago PME), in collaboration with scientists at New York University (NYU), have uncovered how the molecular structure of ion-exchange membranes changes in the presence of water, providing new design principles for next-generation clean energy technologies such as fuel cells and water electrolyzers.
The study reveals that the polymer backbone of ion-exchange membranes plays a critical role in determining their nanostructure, water distribution, and ion conductivity. The findings could help engineers develop more efficient, durable, and environmentally friendly membranes for energy conversion and industrial separation technologies.
Water Reshapes Membrane Nanostructures
Ion-exchange membranes are essential components of fuel cells and electrolyzers because they allow only water and specific ions to pass through. Their efficiency largely depends on how effectively they transport ions while maintaining mechanical stability.
To better understand this process, researchers investigated how different polymer backbone chemistries influence membrane structure and performance. They discovered that the membranes’ nanostructures evolve as water moves through them, and these structural changes are strongly influenced by the stiffness and flexibility of the polymer backbone.
The study found that flexible polymer backbones create distinct ionic nanostructures that enable higher ion conductivity with lower water uptake, overcoming a long-standing trade-off between conductivity and structural stability.
“The combination of experiment and molecular simulation is key to developing a fundamental understanding of these materials and the molecular-level connections,” said Prof. Paul Nealey, who co-authored the study.
Greener Hydrocarbon-Based Membranes Show Promise
The research focused on anion-conducting polyelectrolytes (ACPs)—positively charged polymers that transport negatively charged ions through the membrane.
The team synthesized and analyzed three different ACPs with varying backbone architectures, including one provided by the Georgia Institute of Technology. Unlike conventional membranes that rely on fluoropolymers, the researchers used hydrocarbon-based polymers, which are considered more environmentally friendly and potentially more stable.
“These hydrocarbon materials are very promising, both from an environmental perspective and from a stability standpoint. But we still need fundamental research to better understand how they work,” said Mincheol Kim, a UChicago PME graduate student and lead author of the study.
Simulations Reveal Atomic-Level Insights
Using a combination of laboratory experiments and molecular dynamics simulations, the researchers observed how well-defined ionic nanostructures formed and evolved as water entered the membranes.
The simulations, led by Ge Sun of NYU and Prof. Juan de Pablo, Executive Dean of the NYU Tandon School of Engineering, provided atomic-level insights into structural differences that could not be captured through experiments alone.
The researchers found that these well-organized nanostructures create more efficient ion-conducting pathways while limiting excess water absorption—a key factor in improving membrane durability and performance.
“Rather than identifying a single optimal backbone, our work establishes design principles,” Kim explained. “Different backbone chemistries create different ionic nanostructures, and those nanostructures determine how much water the membrane actually needs to transport ions efficiently.”
Toward Better Energy and Separation Technologies
The research team will next investigate how different counterions influence water movement and membrane morphology to further optimize membrane performance.
According to Associate Professor Shrayesh Patel, the findings provide valuable molecular-level guidelines for designing future anion-conducting polyelectrolytes.
“This work offers molecular-level design guidelines for next-generation ACPs. It is the beginning of helping design more environmentally friendly membranes broadly relevant to energy conversion, separations, and critical minerals recovery.”
The study advances the understanding of ion-exchange membrane design and could contribute to the development of more efficient fuel cells, water electrolyzers, industrial separation systems, and technologies for recovering critical minerals, supporting the transition to cleaner and more sustainable energy systems.
