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.

It’s official: AOL’s dial-up internet has taken its last bow.

AOL previously confirmed it would be pulling the plug on Tuesday (Sept. 30)—writing in a brief update on its support site last month that it “routinely evaluates” its offerings and had decided to discontinue dial-up, as well as associated software “optimized for older operating systems,” from its plans.

Dial-up is now no longer advertised on AOL’s website. As of Wednesday, former company help pages like “connect to the internet with AOL Dialer” appeared unavailable—and nostalgic social media users took to the internet to say their final goodbyes.

AOL, formerly America Online, introduced many households to the World Wide Web for the first time when its dial-up service launched decades ago, rising to prominence particularly in the 90s and early 2000s.

The creaky door to the internet was characterized by a once-ubiquitous series of beeps and buzzes heard over the phone line used to connect your computer online—along with frustrations of being kicked off the web if anyone else at home needed the landline for another call, and an endless bombardment of CDs mailed out by AOL to advertise free trials.

Eventually, broadband and wireless offerings emerged and rose to dominance, doing away with dial-up’s quirks for most people accessing the internet today—but not everyone.

A handful of consumers have continued to rely on internet services connected over telephone lines. In the U.S., according to Census Bureau data, an estimated 163,401 households were using dial-up alone to get online in 2023, representing just over 0.13% of all homes with internet subscriptions nationwide.

While AOL was the largest dial-up internet provider for some time, it wasn’t the only one to emerge over the years. Some smaller internet providers continue to offer dial-up today. Regardless, the decline of dial-up has been a long time coming. And AOL shutting down its service arrives as other relics of the internet’s earlier days continue to disappear.

Microsoft retired video calling service Skype just earlier this year—as well as Internet Explorer back in 2022. And in 2017, AOL discontinued its Instant Messenger—a chat platform that was once lauded as the biggest trend in online communication since email when it was founded in 1997, but later struggled to ward off rivals.

AOL itself is far from the dominant internet player it was decades ago—when, beyond dial-up and IMs, the company also became known for its “You’ve got mail” catchphrase that greeted users who checked their inboxes, as famously displayed in the 1998 film starring Tom Hanks and Meg Ryan by the same name.

Before it was America Online, AOL was founded as Quantum Computer Services in 1985. It soon rebranded and hit the public market in 1991. Near the height of the dot-com boom, AOL’s market value reached nearly $164 billion in 2000. But tumultuous years followed, and that valuation plummeted as the once-tech pioneer bounced between multiple owners. After a disastrous merger with Time Warner Inc., Verizon acquired AOL—which later sold AOL, along with Yahoo, to a private equity firm.

AOL now operates under the larger Yahoo name. A spokesperson for Yahoo didn’t have any additional statements about the end of AOL’s dial-up when reached by The Associated Press on Wednesday—directing customers to its previous summer announcement.

At the time Verzion it sold AOL in 2021, an anonymous source familiar with the transaction told CNBC that the number of AOL dial-up users was “in the low thousands”—down from 2.1 million when Verzion first moved to acquire AOL in 2015, and far below peak demand seen back in the 90s and early 2000s. But beyond dial-up, AOL continues to offer its free email services, as well as subscriptions that advertise identity protection and other tech support.

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