Hydrogen society could be one step closer after storage tech breakthrough

Oliver Trebilcock

Hyundai's ix35 hydrogen car (Credit: iStock)
Hyundai's ix35 hydrogen car (Credit: iStock)

Researchers may have solved a key technical challenge with hydrogen storage, paving the way for industrial applications and widespread hydrogen cars.

Many current solutions are too energy-intensive or too heavy, a University of California, Davis-led team said. In response, they developed a strong and lightweight porous nanofoam, taking inspiration from the pore-filled bone and cork from nature.

Crucially, palladium nanofoams and those made from certain other metals can rapidly store and release hydrogen, giving them enormous potential for use in hydrogen fuel cells for powering cars and industrial applications.

While there are relatively few hydrogen cars on the market today, led by Toyota’s Mirai, Japan is pushing the technology as a key source of energy for the future of the country – a “hydrogen society”. It aims to showcase the technology to the world at the 2020 Tokyo Olympics. Metallic foam may help to achieve their vision.

Traditional metallic foam manufacturing requires high temperatures and pressures, as well as controlled chemical environments. The team solved this problem with a wet chemistry (liquid) approach, which senior study author Kai Liu claims is both well-suited to industrial applications and adaptable to other types of lightweight metal foams as well.

"This opens up a whole new platform for exciting materials explorations," said Liu, professor of physics in the UC Davis College of Letters and Science.

This excitement is shared by Tim Mays, professor of chemical and materials engineering at the University of Bath, and co-director of the SUPERGEN Hydrogen and Fuel Cell Research Hub. The nanofoams are “fascinating and may well find use in a number of technological applications, especially as the materials appear to have tuneable densities unlike many current low density metal foams,” he told PE.

“The most attractive aspect appears to be the processing method,” Duncan H. Gregory, professor and chair in inorganic materials at the University of Glasgow, told PE. "This is a relatively easy and sustainably green way of making a palladium foam…

“As a catalyst the material could be very interesting and perhaps there are both structural and functional composites that could be formed by using the palladium foam as a scaffold and filling.”

Liu’s team have managed to achieve the difficult task of creating extremely lightweight nanofoams without compromising their stability – creating a density of material as low as one-thousandth of the density of palladium in its bulk metal form. Like strong, lightweight bones in the human body, this makes the material dramatically more useful for a whole range of applications. It can also be tuned to be optimized for each different use.

The building blocks of the new technique are palladium nanowires. These nanowires are put in water, then mixed into a slurry with ultrasonic vibrations, and finally quickly immersed in liquid nitrogen to freeze the wires in place. The resultant ice in the mix then vaporises in a vacuum, leaving behind a pure palladium nanowire foam – hundreds of times lighter than the original palladium.

The hydrogen storage properties of this palladium nanofoam have been found by the researchers to be incredibly promising, with them claiming the material demonstrates excellent rates of absorption and storage of the hydrogen. The nanofoam has also been shown to exhibit excellent thermodynamic stability, at a laboratory led by distinguished physical chemist and study co-author Alexandra Navrotsky.

However, Mays points out that challenges with this method of hydrogen storage remain.

He added: “Use of LD foams for hydrogen storage present challenges including a lack of mechanical robustness due to their low density, and in this case also relatively low gravimetric H2 capacities (levels of hydrogen storage) which are way below US Department of Energy targets.”

The results are published in Chemistry of Materials, and the research team are now moving on to pursue several new uses for these strong, lightweight nanofoam materials, which Gregory says are arguably the most exciting applications, yet to be explored.


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