A wet chemistry approach to manufacture palladium nanofoams overcomes the challenges inherent with traditional metallic foam manufacturing techniques: high-pressure, high-temperature, and controlled environments.
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. 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 and this requires overcoming various challenges, including demanding manufacturing conditions. In fact, traditional metallic foam manufacturing techniques tend to require high temperatures, high pressures and controlled chemical environments.
The new method, developed by UC Davis researchers, 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 team also studied the hydrogen-storage properties of the palladium nanofoam. They discovered that the material demonstrated excellent loading capacity and rate of absorption. The nanofoam exhibits excellent thermodynamic stability, as measured by specialized calorimetric techniques at the UC Davis Peter A. Rock Thermochemistry Laboratory.