Palladium filters can enable cheaper, more efficient generation of hydrogen fuel

Palladium is one of the keys to start a hydrogen-based energy economy. The silver metal is a natural gatekeeper against any gas except hydrogen, which easily lets through. For its exceptional selectivity, Palladium is considered one of the most effective materials in filtering gas mixtures to produce pure hydrogen.

Nowadays, palladium -based membranes are used on a commercial scale to offer pure hydrogen for the production of semiconductors, food processing and production of fertilizers, in addition to other applications in which the membranes work at modest temperatures. If palladium membranes become much hotter than around 800 Kelvin, they can break.

Now MIT ingieurs have developed a new palladium membrane that remains resilient at much higher temperatures. Instead of being made as a continuous film, as most membranes are, the new design is made of palladium that is deposited as “plugs” in the pores of an underlying supporting material. At high temperatures, the close -fitting plugs remain stable and continue to separate hydrogen, instead of breaking down as a surface film would do.

The thermally stable design opens opportunities for membranes to use in hydrogen-generating technologies such as compact steam methane reform and ammonia cracks that are designed to work at much higher temperatures to produce hydrogen-carbon-carbon-emittering fuel.

“With further work on scaling and validating performance under realistic industrial feeds, the design could be a promising route to practical membranes for hydrogen production at high temperature,” says Lohyun Kim Ph.D. ’24, a former graduate student in the Mituankiektie Department of MIT.

Kim and his colleagues report details of the new membrane in one Study that appears today in the diary Advanced functional materials. The co-authors of the study are Randall Field, director of research at the MIT Energy Initiative (Mitei); Former graduate Mit Chemical Engineering student Chun Man Chow Ph.D. ’23; Rohit Karnik, the Jameel professor at the Mechanical Engineering department 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 that is now a university teacher at the Eastern Shore of the University of Maryland.

Compact future

The new design of the team came from a Mitei project with regard to Fusion Energy. Future merger -power plants, such as the One with Spinout Commonwealth Fusion Systems designswill relate to circulating hydrogen isotopes from Deuterium and Tritium at extremely high temperatures to produce energy through the combination of the isotopes. The reactions inevitably produce other gases that must be separated, and the hydrogen isotopes will be recirculated in the main reactor for further merger.

Similar problems occur in a number of other processes for producing hydrogen, where gases must be separated and recovered in a reactor. Concepts for such recirculation systems should first cool the gas before it can go through hydrogen separation membranes-an expensive and energy-intensive step that would include extra machines and hardware.

“One of the questions we thought about: can we develop membranes that can be as close as possible to the reactor and can work at higher temperatures, so we don’t have to pull the gas out and cool it first?” Says Karnik. “It would make it more energy-efficient and therefore make cheaper and compact merging systems possible.”

The researchers were looking for ways to improve the temperature resistance of palladium membranes. Palladium is the most effective metal that is nowadays used to separate hydrogen from different gas mixtures. It naturally attracts hydrogen molecules (H₂) To the surface, where the electrons of the metal interact with and the bonds of the molecule weaken, through which H₂ To temporarily break apart in his respective atoms. The individual atoms then diffuse through the metal and join again on the other side as pure hydrogen.

Palladium is very effective in penetrating hydrogen, and only hydrogen, of streams of different gases. But conventional membranes can usually work at temperatures of up to 800 Kelvin before the film starts to form holes or lumps in drops, so that other gases can flow through it.

Connect

Karnik, Kim and their colleagues took a different design approach. They saw that palladium will start shrinking at high temperatures. The material works in technical terms to reduce the surface energy. To do this, palladium and most other materials and even water will pull apart and form drops 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 the pores of a supporting material can be “connected” with deposits of palladium – which are essentially a drop with the lowest surface energy – the tight quarters could considerably increase the heat tolerance of palladium, while retaining the selection of the membrane for hydrogen.

To test this idea, they manufactured small chip-format samples of membrane using a porous silica-supporting layer (every pore that was about half a micron wide), on which they deposit a very thin layer of palladium. They brought techniques to allow the palladium to grow in the pores and polished through the surface to remove the palladium layer and leave palladium only in the pores.

They then placed samples in a tailor -made device in which they flowed hydrogen -containing gas from different mixtures and temperatures to test the separation performance. The membranes remained stable and continued to separate hydrogen from other gases, even after experiencing temperature up to 1,000 Kelvine for more than 100 hours a significant improvement compared to conventional film-based membranes.

“The use of palladium film membranes is generally limited to under about 800 Kelvin, at what point they break down,” says Kim. “Our plug design therefore expands the effective heating power of Palladium with at least 200 Kelvin and maintains integrity for much longer under extreme conditions.”

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

Reforming steam methane is a set process that requires complex, energy-intensive systems to process methane for a form where pure hydrogen can be extracted. Such pre -processing steps can be replaced by a compact “membrane reactor”, so that a methane gas would flow directly, and the membrane inside would filter pure hydrogen.

Such reactors would significantly reduce the size, complexity and costs for producing hydrogen by steam methane reform and Kim estimates that a membrane should work reliably on temperatures up to almost 1,000 Kelvin. The new membrane of the team could work well within such circumstances.

Ammonia cracking is another way to produce hydrogen, by “cracking” ammonia apart or breaking apart. Because ammonia is very stable in liquid form, scientists propose that it can be used as a hydrogen carrier and are transported safely to a hydrogen station, whereby ammonia can be used in a membrane reactor that again pulls out hydrogen and pumps it directly into a fuel cell vehicle.

Ammonia Kraken is still largely in pilot and demonstration stages, and Kim says that every membrane in an ammonia crack reactor would probably work at temperatures of around 800 Kelvin-the range of the new plug-based design of the group.

Karnik emphasizes that their results are just a start. Taking over the membrane in working reactors requires further development and testing to ensure that it remains reliable for much longer time.

“We have shown that instead of making a movie, if you make discreted nanostructures, you can get much more thermally stable membranes,” says Karnik. “It offers a path for designing membranes for extreme temperatures, with the extra possibility of using smaller quantities of expensive palladium, to make hydrogen production more efficient and more affordable. There is potential there.”

This story has been re -published thanks to MIT News (Web.mit.edu/newsoffice/), A popular site that deals with news about MIT research, innovation and education.