Palladium is one of the keys to jump-starting a hydrogen-based energy economy. The silvery metal is a natural gatekeeper against every gas except hydrogen, which it readily lets through. For its exceptional selectivity, palladium is considered one of the most effective materials at filtering gas mixtures to produce pure hydrogen.

Today, palladium-based membranes are used at commercial scale to provide pure hydrogen for semiconductor manufacturing, food processing, and fertilizer production, among other applications in which the membranes operate at modest temperatures. If palladium membranes get much hotter than around 800 Kelvin, 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 made from palladium that is deposited as “plugs” into the pores of an underlying supporting material. At high temperatures, the snug-fitting plugs remain stable and continue separating out hydrogen, rather than degrading as a surface film would.

The thermally stable design opens opportunities for membranes to be used in hydrogen-fuel-generating technologies such as compact steam methane reforming and ammonia cracking—technologies that are 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 Ph.D. ’24, a former graduate student in MIT’s Department of Mechanical Engineering.

Kim and his colleagues report details of the new membrane in a study appearing today 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 Ph.D. ’23; 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.

Compact future

The team’s new design came out of a MITEI project related to fusion energy. Future fusion power plants, such as the one MIT spinout Commonwealth Fusion Systems is designing, will involve circulating hydrogen isotopes of deuterium and tritium at extremely high temperatures to produce energy from the isotopes’ fusing. The reactions inevitably produce other gases that will have to be separated, and the hydrogen isotopes will be recirculated into the main reactor for further fusion.

Similar issues arise in a number of 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—an expensive and energy-intensive step that 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 looked for ways to improve 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 temporarily break apart into its respective atoms. The individual atoms then diffuse through the metal and join back up 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 Kelvin before the film starts to form holes or clumps 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 up. In engineering terms, the material is acting to reduce surface energy. To do this, palladium, and most other materials and even 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 essentially grow the palladium into the pores, and polished down the surface to remove the palladium layer and leave palladium only inside the pores.

They then placed samples in a custom-built apparatus in which 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 after experiencing temperatures of up to 1,000 Kelvin for over 100 hours—a significant improvement over conventional film-based membranes.

“The use of palladium film membranes are generally limited to below around 800 Kelvin, at which point they degrade,” Kim says. “Our plug design therefore extends palladium’s effective heat resilience by roughly at least 200 Kelvin 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 has required 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 a methane gas would directly flow, and the membrane inside would filter out pure hydrogen.

Such reactors would significantly cut down the size, complexity, and cost of producing hydrogen from steam methane reforming, and Kim estimates a membrane would have to work reliably in temperatures of up to nearly 1,000 Kelvin. 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. As ammonia is very stable in liquid form, scientists envision that it could be used as a carrier for hydrogen and be safely transported to a hydrogen fuel station, where ammonia could be fed into a membrane reactor that again 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 of around 800 Kelvin—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 story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Yan Yao, a professor at University of Houston’s Cullen College of Engineering, along with collaborators from Singapore, Zhejiang University and Seoul National University, have published a review in the journal Science eying alternative metals for battery anodes.

If Yao and his fellow collaborators succeed, it could lead to longer-lasting batteries for electric vehicles, smartphones, laptops and more.

“I think the most exciting part of this is the global interest in this new battery,” Yao said. “But we still have a lot of challenges ahead; there’s still a lot of learning that needs to be done.”

The review highlights the similarities and differences in monovalent metals such as lithium, sodium and potassium, and multivalent metals, including magnesium, calcium and aluminum.

The impetus for this review is that graphite, the standard anode for lithium-ion batteries, is reaching its practical limits. Lithium metal could be a strong alternative as it offers 10 times the charge storage capacity of graphite, but it tends to form tiny spikes called dendrites that can short-circuit batteries.

Meanwhile, multivalent metals present promising alternatives because they are more abundant, safer and potentially able to store more energy at a lower cost. The downside to these metals is multivalent ions move more slowly, which can slow charging, but are less prone to forming dendrites.

To overcome these barriers, researchers are exploring textured electrode surfaces that guide smooth metal growth and developing new electrolytes that optimize ion movement and protective film formation.

“This work underscores the need for continued research to overcome the technical barriers of multivalent metal batteries,” Yao said. “Advances in electrode design, electrolyte chemistry, and battery architecture are crucial to harness the full potential of these materials.”

The study also identifies emerging design principles, such as using locally high salt concentrations and weakly solvating electrolytes for monovalent systems, and strongly solvating, weakly ion-pairing electrolytes for multivalent systems, offering a roadmap for next-generation electrolyte development.

Other contributors include Yuanjian Li, Sonal Kumar, Gaoliang Yang and Zhi Wei Seh from the Institute of Materials Research and Engineering (IMRE) in Singapore; Jun Lu from Zhejiang University; and Kisuk Kang from Seoul National University.

With global demand for high-performance, sustainable batteries growing, this research provides critical guidance for scientists and engineers striving to develop the next generation of energy storage technologies.

Hi. it turns out Prime Day is only really a suggestion on the calendar. A lot of brands like to kick out early Prime Day deals before getting lost in the big din of Prime Big Deal Days on October 7-8. (See here for early Prime Day deals on laptops, earbuds, and more.)

The two most popular espresso machines on Earth—as judged by Amazon sales, anyway–are both on sale for $100 off this week, ahead of Amazon Prime Day’s October reprise. These are a couple of the best early Prime Day Deals.

$100 off Ninja Luxe Cafe Premier Before Prime Day

The most exciting deal of the pair is probably the Ninja Luxe Cafe Premier ($500), on sale for the lowest price we’ve ever seen it.

When Ninja announced it was jumping into the semiautomatic espresso market, I didn’t know quite what to make of it. But Ninja seems to have applied its general flair for multipurpose machines to this beautifully beginner-friendly espresso machine with a 25-setting conical burr grinder, a built-in scale (thank you), and options for cold brew and drip coffee.

WIRED contributing reviewer Tyler Shane was likewise skeptical of Ninja’s first espresso device when it arrived but ended up loving the excellent milk steaming and the fact that this Ninja grinds espresso shots by weight. (Why doesn’t everybody?) She also appreciated the reasonable price—a price that’s even more reasonable ahead of Prime Day.

$100 off Breville Barista Express

Courtesy of Breville

Breville’s Barista Express ($600) semiautomatic espresso machine has been Amazon’s best-selling espresso machine for years—so long it’s hard to remember a time when it wasn’t the top-selling pick.

Why’s it so popular? It’s a Goldilocks thing—a mix of accessible price, Breville’s excellent reputation for customer service on high-ticket items, and beautiful ease of use on a semiautomatic machine with a built-in grinder that makes full-flavored, well-extracted espresso. This $100 discount isn’t quite the lowest price we’ve seen on it—it’s been down to $550 before—but it’s a very good price.

And besides, this Breville has the merit of being a tried-and-true machine. WIRED reviewer Julian Chokkattu has been pulling shots from his Barista Express for six years now, and it’s still going strong. No wonder the Express has been among WIRED’s top espresso machine picks for ages.