This is a microscope image of the palladium nanofoam developed by the UC Davis-led team. Image: Dustin Gilbert and Kai Liu, UC Davis.
This is a microscope image of the palladium nanofoam developed by the UC Davis-led team. Image: Dustin Gilbert and Kai Liu, UC Davis.

A simple method for manufacturing extremely low-density palladium nanofoams could help advance hydrogen storage technologies, say researchers at the University of California (UC), Davis. The researchers report their findings in a paper in Chemistry of Materials.

A nanofoam is what it sounds like – a foamy version of a material, filled with very small pores. First developed about 20 years ago, metallic nanofoams have potential for use in a diverse range of applications. The porous structures are strong and lightweight – like their natural counterparts of bone and cork. Palladium and certain other metal nanofoams can also rapidly store and release hydrogen, making them an ideal candidate for hydrogen fuel cells.

In order for cars to be refueled with nanofoams, however, they need to be produced on an industrial scale. This requires overcoming various challenges, including demanding manufacturing conditions, contamination and poor crystallinity, said senior author Kai Liu, professor of physics in the UC Davis College of Letters and Science. It is also difficult to produce extremely lightweight foams without compromising their stability, Liu noted.

Traditional metallic foam manufacturing techniques tend to require high temperatures, high pressures and controlled chemical environments. By contrast, the manufacturing method developed by the UC Davis-led team relies on a wet chemistry approach that is well-suited for industrial applications and adaptable to other types of lightweight metal foams as well.

"This opens up a whole new platform for exciting materials explorations," Liu said.

Their new method uses nanowires of palladium as building blocks. These nanowires are put in water and mixed into a slurry using ultrasonic vibrations; the slurry is then quickly immersed in liquid nitrogen to freeze the wires in place. Finally, the ice-nanowire mix is placed in a vacuum until the ice vaporizes, leaving behind a pure palladium nanowire foam. The density of the foam is as low as one-thousandth of the density of palladium in its bulk metal form and can be tuned for different applications, the team found.

The researchers also studied the hydrogen storage properties of their palladium nanofoam, finding that the material demonstrated excellent loading capacity and rate of absorption. The nanofoam also exhibits excellent thermodynamic stability, as measured by specialized calorimetric techniques at the UC Davis Peter A. Rock Thermochemistry Laboratory.

This story is adapted from material from the University of California, Davis, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.