DESY nano-chocolates that store hydrogen

Announced just before the end of 2021, a team led by the Deutsches Elektronen-Synchrotron or DESY research center, laid the foundation for an alternative method of storing hydrogen gas using palladium nanoparticles wrapped around a core of iridium, which can attract and accumulate hydrogen like a kind of chocolate glaze.

Considered a promising energy carrier of the future, hydrogen as fuel presents its own set of problems and challenges. Although a suitable and potentially climate-friendly energy source for airplanes, ships, and large industrial applications, it is highly volatile.

Furthermore, storing hydrogen is costly: either the gas must be kept in highly pressurized tanks, or it must be liquified, which means cooling it down to minus 253 degrees Celsius (minus 423 degrees Fahrenheit).

Both procedures consume additional energy.

A team led by DESY's Andreas Stierle has proposed a new method: storing hydrogen in tiny nanoparticles made of the precious metal palladium, just 1.2 nanometers in diameter.

The fact that palladium can absorb hydrogen like a sponge has been known for some time.

"However, until now, getting the hydrogen out of the material again has posed a problem," Stierle explains. "That's why we are trying palladium particles that are only about one nanometer across."

A nanometer is a millionth of a millimeter.

To ensure these nanoparticles are sufficiently sturdy, they are stabilized by a core made of the rare precious metal iridium. In addition, they are attached to a graphene support.

"We are able to attach the palladium particles to the graphene at intervals of just two and a half nanometres," said Stierle, who is the head of the DESY NanoLab. "This results in a regular, periodic structure."

The team, which also includes researchers from the universities of Cologne and Hamburg, published its finding in the American Chemical Society (ACS) journal "ACS Nano."

DESY is a national research center located in Germany that operates particle accelerators much like the renowned CERN and its Hadron Collider.

The research center's X-ray source PETRA III was used to observe what happens when the palladium particles come into contact with hydrogen – essentially, the hydrogen sticks to the nanoparticles' surfaces, with hardly any of it penetrating inside.

Likened to chocolates-with an iridium nut in the center, enveloped in a layer of palladium, rather than marzipan, and finally coated with an outside layer of chocolate (hydrogen). All it takes to recover the stored hydrogen is to melt the chocolate just so for the hydrogen particles to rapidly release from the surface.

"Next, we want to find out what storage densities can be achieved using this new method," said Stierle.

However, some challenges still need to be overcome before proceeding to practical applications. For example, other forms of carbon structures might be a more suitable carrier than graphene – the researchers are considering using carbon sponges, containing tiny pores. In this case, substantial amounts of palladium nanoparticles would be capable of fitting inside.