Palladium is a key to jumpstarting a hydrogen-based energy economy. The silvery metal acts as a natural gatekeeper against every gas except hydrogen, which it readily allows through. For its exceptional selectivity, palladium is considered one of the most effective materials for filtering gas mixtures to produce pure hydrogen.

Today, palladium-based membranes are used on a commercial scale to provide pure hydrogen for semiconductor manufacturing, food processing, and fertilizer production, among other applications where the membranes operate at modest temperatures. If palladium membranes get much hotter than 800 kelvins, they can break down.

Now, MIT engineers have developed a new palladium membrane that remains resilient at much higher temperatures. Rather than being made as a continuous film, as most membranes are, the new design is composed of palladium deposited as “plugs” into the pores of an underlying supporting material. At high temperatures, the snug-fitting plugs remain stable and continue separating hydrogen rather than degrading as a surface film would.

The thermally stable design opens up opportunities for membranes to be used in hydrogen fuel-generating technologies such as compact steam methane reforming and ammonia cracking—technologies designed to operate at much higher temperatures to produce hydrogen for zero carbon-emitting fuel and electricity.

“With further work on scaling and validating performance under realistic industrial feeds, the design could represent a promising route toward practical membranes for high-temperature hydrogen production,” says Lohyun Kim, a graduate student in MIT’s Department of Mechanical Engineering.

Kim and his colleagues report details of the new membrane in a study published in the journal Advanced Functional Materials. The study’s co-authors are Randall Field, director of research at the MIT Energy Initiative (MITEI); former MIT chemical engineering graduate student Chun Man Chow; Rohit Karnik, the Jameel Professor in the Department of Mechanical Engineering at MIT and the director of the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS); and Aaron Persad, a former MIT research scientist in mechanical engineering who is now an assistant professor at the University of Maryland Eastern Shore.

Palladium plug membrane at the end of the membrane fabrication process (left). Dashed green lines outline the membrane. Scanning electron microscopy image of the membrane shows the palladium plugs embedded inside the pores of the silica support (right). Credit: Lohyun Kim 

Compact future

The team’s new design emerged from an MITEI project related to fusion energy. Future fusion power plants—like the one being designed by MIT spinout Commonwealth Fusion Systems—will circulate hydrogen isotopes of deuterium and tritium at extremely high temperatures to produce energy from the isotopes’ fusing.

The reactions inevitably produce other gases that must be separated, and the hydrogen isotopes will be recirculated into the main reactor for further fusion.

Similar issues arise in several other processes for producing hydrogen, where gases must be separated and recirculated back into a reactor. Concepts for such recirculating systems would require first cooling down the gas before it can pass through hydrogen-separating membranes. This expensive and energy-intensive step would involve additional machinery and hardware.

“One of the questions we were thinking about is: Can we develop membranes which could be as close to the reactor as possible, and operate at higher temperatures, so we don’t have to pull out the gas and cool it down first?” Karnik says. “It would enable more energy-efficient, and therefore cheaper and compact fusion systems.”

The researchers sought ways to enhance the temperature resistance of palladium membranes. Palladium is the most effective metal used today to separate hydrogen from a variety of gas mixtures. It naturally attracts hydrogen molecules (H₂) to its surface, where the metal’s electrons interact with and weaken the molecule’s bonds, causing H₂ to break apart into its respective atoms temporarily. The individual atoms then diffuse through the metal and reassemble on the other side as pure hydrogen.

Palladium is highly effective at permeating hydrogen, and only hydrogen, from streams of various gases. But conventional membranes typically can operate at temperatures of up to 800 kelvins before the film starts to form holes or clump up into droplets, allowing other gases to flow through.

Plugging in

Karnik, Kim, and their colleagues took a different design approach. They observed that at high temperatures, palladium will start to shrink. In engineering terms, the material acts to reduce surface energy. To do this, palladium and most other materials, as well as water, will pull apart and form droplets with the smallest surface energy. The lower the surface energy, the more stable the material can be against further heating.

This gave the team an idea: If a supporting material’s pores could be plugged with deposits of palladium—essentially already forming a droplet with the lowest surface energy—the tight quarters might substantially increase palladium’s heat tolerance while preserving the membrane’s selectivity for hydrogen.

To test this idea, they fabricated small chip-sized samples of membrane using a porous silica supporting layer (each pore measuring about half a micron wide), onto which they deposited a very thin layer of palladium. They applied techniques to grow the palladium into the pores, essentially, and then polished the surface to remove the palladium layer, leaving palladium only inside the pores.

They then placed samples in a custom-built apparatus where they flowed hydrogen-containing gas of various mixtures and temperatures to test its separation performance. The membranes remained stable and continued to separate hydrogen from other gases, even at temperatures up to 1,000 kelvins for more than 100 hours —a significant improvement over conventional film-based membranes.

“The use of palladium film membranes is generally limited to below around 800 kelvins, at which point they degrade,” Kim says. “Our plug design therefore extends palladium’s effective heat resilience by at least 200 kelvins and maintains integrity far longer under extreme conditions.”

These conditions are within the range of hydrogen-generating technologies such as steam methane reforming and ammonia cracking.

Steam methane reforming is an established process that requires complex, energy-intensive systems to preprocess methane to a form where pure hydrogen can be extracted. Such preprocessing steps could be replaced with a compact “membrane reactor,” through which methane gas would flow directly, and the membrane inside would filter out pure hydrogen. Such reactors would significantly reduce the size, complexity, and cost of hydrogen production from steam methane reforming. Kim estimates a membrane would have to work reliably at temperatures up to nearly 1,000 kelvins. The team’s new membrane could work well within such conditions.

Ammonia cracking is another way to produce hydrogen, by “cracking,” or breaking apart, ammonia. Because ammonia is very stable in its liquid form, scientists envision that it could be used as a carrier for hydrogen and safely transported to a hydrogen fuel station, where ammonia can be fed into a membrane reactor that pulls out hydrogen and pumps it directly into a fuel cell vehicle. Ammonia cracking is still largely in pilot and demonstration stages, and Kim says any membrane in an ammonia cracking reactor would likely operate at temperatures around 800 kelvins—within the range of the group’s new plug-based design.

Karnik emphasizes that their results are just a start. Adopting the membrane into working reactors will require further development and testing to ensure it remains reliable over much longer periods of time.

“We showed that instead of making a film, if you make discretized nanostructures you can get much more thermally stable membranes,” Karnik says. “It provides a pathway for designing membranes for extreme temperatures, with the added possibility of using smaller amounts of expensive palladium toward making hydrogen production more efficient and affordable. There is potential there.”

This effort was supported by Eni SpA via the MIT Energy Initiative. The work used facilities at the MIT Materials Research Laboratory (MRL), the MIT Laboratory for Manufacturing and Productivity (LMP), and MIT.nano.

Published Oct. 1, 2025, by MIT News.