The nanoparticle clusters, which look a lot like fancy chocolates, could make hydrogen storage easy and provide a reliable fuel source for planes, cars and ships.
Hydrogen — which can be separated out of water, biomass or fossil fuels — can work as a carrier, allowing energy from other sources to 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 unit of weight — three times that of petrol.
And unlike conventional fuels, its use in a fuel cell (through combination with oxygen) produces only water — a perfectly harmless by-product.
However, hydrogen is volatile and is one of its problems. It is therefore difficult to store it.
To contain it, you either need a tank pressurised to around 700 times the atmospheric pressure at sea level, or one chilled down to around -423°F (-253°C).
These solutions are more energy-intensive to keep going.
Experts led from the Deutsches Elektronen-Synchrotron (DESY) may have a better solution, one that sees the gas trapped on the surface of tiny palladium particles.
Each so-called ‘nanocluster’ is only 1.2 nanometres in diameter — just a few atoms across — and can store hydrogen at ambient conditions.
You can heat them to make hydrogen, then cool and reuse.
Not only is it a cleaner source of fuel but there could be more efficient ways to store hydrogen which would allow new, climate-friendly methods to produce cement and steel.
Nanoparticle clusters structured a bit like fancy chocolates (pictured) could be key to making hydrogen easy to store — unlocking a climate friendly fuel for cars, ships and planes
According to the team — led by DESY nanoscientist Andreas Stierle — the fact that palladium can soak up hydrogen like a sponge has been known for some time.
Professor Stierle stated that obtaining the hydrogen from the materials has been a challenge until now.
‘That’s why we are trying palladium particles that are only about one nanometre across,’ he added, noting that a nanometre is a millionth of millimetre.
This team has a brilliant solution. The hydrogen sticks to the surface of palladium instead of inside, which makes it much easier to recover.
The team placed each cluster around the stabilizing core of the precious metal, iridium to ensure that they are strong enough.
They have a ‘fancy-sweet’ structure that is similar to what you get when you wrap a layer marzipan around the hazelnut core.
The hydrogen stored in this way is like the coating of chocolate that sticks to the marzipan’s surface.
And all that is needed to release the fuel is a little heat — much in the same way that heating the confectionary would melt the chocolate off!
The team placed each nanocluster around an iridium core to ensure that they are strong enough. They have a ‘fancy-sweet’ structure that resembles a marzipan layer wrapped around a hazelnut center. The hydrogen stored in this way is analogous to the coating of chocolate that sticks on the marzipan’s surface. A box of chocolates
Each cluster is anchored to an underlying layer of graphene — a thin sheet of carbon atoms arranged in a hexagonal pattern — which in turns rest on an iridium base. These could be the tissue paper or the box.
Professor Stierle stated that he was able to attach the Palladium particles to graphene within a range of two-and-a-half nanometres.
He added, “This creates a periodic, regular structure.”
In tests of a prototype of the nanocluster storage system, the team used DESY’s ‘PETRA III’ X-ray source to observe what happens when hydrogen comes into contact with the palladium of the nanoclusters.
They were able to confirm that the hydrogen overwhelmingly sticks to the outside of each nanocluster — with hardly any of the fuel penetrating inside the particles.
Each cluster is anchored to an underlying layer of graphene — a thin sheet of carbon atoms arranged in a hexagonal pattern — which in turns rest on an iridium base. They could also be sheets of tissue paper, or even the chocolate box. One nanocluster view from the side. These are the red atoms of iridium and blue carbon, while those with yellow and grey atoms make up palladium. You would expect the hydrogen to stick to the surface on the palladium piece.
‘Next, we want to find out what storage densities can be achieved using this new method,’ said Professor Stierle.
He added that there are a number of challenges to be overcome before the concept might be realised into practical applications — and it may be possible to build better structures by switching out the graphene substrate with a different form of carbon.
One alternative is carbon sponges. These tiny pores could contain substantial amounts of palladium nanoparticles. This would allow for more hydrogen storage in a small volume.
All findings were published in the journal ACS Nano.