New Research Identifies “Bottleneck” in Ion Filtering Membranes

New research out of Lawrence Berkeley National Lab (Berkeley Lab) is helping pave the way for polymer membranes that can filter specific ions—a task that has been a significant challenge in the past. Isolating and recovering specific ions, like lithium, from complex mixtures is important for new applications like lithium mining, battery and magnet recycling, and microelectronics. The study has just been published in the journal Matter.

The Berkeley Lab team was led by faculty scientist Eric Hoek and postdoctoral researcher Ryan Kingsbury in Berkeley Lab’s Energy Storage & Distributed Resources Division. Kingsbury, who is now an assistant professor at Princeton, said, “we set out to locate the ‘bottleneck' that occurs when dissolved minerals such as lithium transport through filtration membranes. It has long been thought that the bottleneck occurs inside the filter, but we showed that it actually occurs at the interface, as the ion moves from the water into the filter (at least for some membranes).”

Using Berkeley Lab’s signature facilities, including the Molecular Foundry, Lawrencium computing cluster, and a novel polymer membrane previously developed by the group of senior scientist Brett Helms, the research team combined kinetic theory, systematic experiments, and first-principles simulations to show that crossing the solution/membrane interface has a higher energy barrier than diffusion. This finding suggests that engineering selective interfaces would be an effective direction for further research.

“Because membrane selectivity appears to be governed primarily by the interactions of different species with the membrane at its interface with the electrolyte, we're now exploring ways to improve transport selectivity through functionalization of the outer membrane surface,” said Brett Helms, senior scientist in Berkeley Lab’s Molecular Foundry.

The findings from this study could have significant ramifications for the future of polymer membrane technology, according to Hoek. “We might be able to develop ion conducting membranes with selective barriers that dramatically enhance fluxes, reduce electrical resistance and lower the cost in the near future,” he said.

This project was supported by the Department of Energy, Laboratory Directed Research and Development program at Lawrence Berkeley National Laboratory. Work at the Molecular Foundry—including polymer synthesis, characterization, membrane fabrication, and testing—was supported by the Department of Energy, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy.