Nanoparticle clusters structured a bit like fancy chocolates can be the key to making hydrogen easy to store and unlock for a climate-friendly fuel for cars, ships and planes.
Hydrogen – which can be separated from water, biomass or fossil fuels – can act as a carrier so that energy from other sources can be stored and moved.
While it takes more energy to get hydrogen than is released by consuming it, it has an attractively high energy content per serving. unit of weight – three times as much as gasoline.
And unlike conventional fuels, its use in a fuel cell (through combination with oxygen) produces only water – a completely harmless by-product.
The problem with hydrogen, however, is that it is a very volatile gas. This means that storing it is just as challenging as it is expensive.
To contain it, you must either have a tank pressurized to about 700 times the atmospheric pressure at sea level, or one cooled to about -423 ° F (-253 ° C).
Both of these solutions require additional energy to maintain.
Experts led by Deutsches Elektronen-Synchrotron (DESY) may have a better solution, one that sees the gas trapped on the surface by small palladium particles.
Each so-called ‘nanocluster’ is only 1.2 nanometers in diameter – only a few atoms across – and can store hydrogen under ambient conditions.
They can be made to release their hydrogen via heating, after which they can be cooled and reused.
In addition to providing a greener source of fuel, more convenient ways of storing hydrogen can enable new, climate-friendly approaches to the production of both cement and steel.
Nanoparticle clusters structured a bit like fancy chocolates (pictured) can be the key to making hydrogen easy to store – unlocking a climate-friendly fuel for cars, ships and planes
To ensure that each nanocluster is sufficiently robust, the team deposited them around a stabilizing core of the precious metal iridium. It’s this that gives them their “fancy sweet” texture, similar to what you would get if you wrapped a layer of marzipan around a hazelnut kernel. In this metaphor, the hydrogen stored is like the chocolate coating that sticks to the surface of the marzipan
According to the team – led by DESY nanoscientist Andreas Stierle – it has been known for some time that palladium can absorb hydrogen like a sponge.
“But until now, it has been a problem to get the hydrogen out of the material again,” Professor Stierle explained.
“That’s why we try palladium particles that are only about one nanometer across,” he added, noting that a nanometer is one millionth of a millimeter.
The genius of the team’s solution is that by using such small particles, the hydrogen ends up sticking to the surface of the palladium instead of inside it, making the fuel significantly easier to recycle.
To ensure that each nanocluster is sufficiently robust, the team deposited them around a stabilizing core of the precious metal iridium.
It’s this that gives them their “fancy sweet” texture, similar to what you would get if you wrapped a layer of marzipan around a hazelnut kernel.
In this metaphor, the hydrogen stored is like the chocolate coating that sticks to the surface of the marzipan.
And all it takes to release the fuel is a little heat – much like heating the confectionery would melt the chocolate!
Each cluster is anchored to an underlying layer of graphene – a thin sheet of carbon atoms arranged in a hexagonal pattern – which in turn rests on an iridium base. In the chocolate box analogy, these can be a sheet of tissue paper and the bottom of the box itself
Each cluster is anchored to an underlying layer of graphene – a thin sheet of carbon atoms arranged in a hexagonal pattern – which in turn rests on an iridium base. In the chocolate box analogy, these can be a sheet of tissue paper and the box itself.
“We are able to bind the palladium particles to the graphene network at intervals of only two and a half nanometers,” Professor Stierle reported.
“This results in a regular, periodic structure,” he added.
In testing a prototype of the nanocluster storage system, the team used DESY’s ‘PETRA III’ X-ray source to observe what happens when hydrogen comes in contact with the palladium of the nanoclusts.
They were able to confirm that the hydrogen overwhelmingly adheres to the outside of each nanocluster – with almost none of the fuel penetrating the particles.
In the picture: a single nanocluster, seen from the side and on. The red atoms are iridium, blue carbon and the yellow and gray atoms are palladium. The hydrogen would adhere to the surface of the palladium moiety
“Next, we will find out what stock densities can be achieved using this new method,” said Professor Stierle.
He added that there are a number of challenges that need to be overcome before the concept can be realized in practical applications – and it may be possible to build better structures by replacing the graphene substrate with another type of carbon.
For example, an alternative that the team is considering is the use of carbon sponges, which contain tiny pores that are likely to each contain “significant amounts” of the palladium nanoparticles, allowing more hydrogen to be stored in a given volume.
The full results of the study were published in the journal ACS Nano.
ABOUT HYDROGEN FUEL CELLS
Hydrogen fuel cells create electricity to power a battery and an engine by mixing hydrogen and oxygen in specially treated plates, which combine to form the fuel cell stack.
Fuel cell stacks and batteries have enabled engineers to shrink these components significantly so that they even fit snugly inside a family car, although they are also commonly used for fuel for buses and other larger vehicles.
Trains and planes are also adapted to run on, for example, hydrogen fuel.
Oxygen is collected from the air through intakes, usually in the grid, and hydrogen is stored in aluminum-lined fuel tanks, which automatically close in an accident to prevent leaks.
These ingredients are molten, releasing usable electricity and water as by-products and making the technology one of the quietest and most environmentally friendly available.
Reducing the amount of platinum used in the stack has made fuel cells cheaper, but the use of the rare metal has limited the prevalence of their use.
Recent research has suggested that hydrogen fuel cell cars may one day challenge electric cars in the race for pollution-free roads, but only if more stations are built to burn them.