Nano-chocolates that store hydrogen

Hydrogen, being a highly volatile gas and Clean energy source, can be considered a promising energy carrier for the future.

However, storing Hydrogen is costly. It either needs to be kept under pressurized tanks at up to 700 bar, or it must be liquified, which means cooling it down to minus 253 degrees Celsius.

Both procedures consume additional energy.

A team led by DESY’s Andreas Stierle has laid the foundations for an alternative method: storing Hydrogen in tiny nanoparticles made of the precious metal palladium, just 1.2 nanometres in diameter. 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 nanometre across.” A nanometre is a millionth of a millimeter.

To ensure that the tiny particles are sufficiently sturdy, they are stabilised by a core made of the rare precious metal iridium. In addition, they are attached to graphene support, an extremely thin layer of carbon. “We are able to attach the palladium particles to the graphene at intervals of just two and a half nanometres,” reports Stierle, who is the head of the DESY NanoLab. “This results in a regular, periodic structure.” The team, including researchers from the Universities of Cologne and Hamburg, published its findings in the American Chemical Society (ACS) journal ACS Nano.

DESY’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 i58nside. The nanoparticles can be pictured as resembling chocolates: an iridium nut at the center, enveloped in a layer of palladium, rather than marzipan, and chocolate-coated on the outside by the Hydrogen. All it takes to recover the stored Hydrogen is for a small amount of heat to be added; the Hydrogen is rapidly released from the particles’ surface because the gas molecules don’t have to push their way out from inside the cluster.

“Next, we want to find out what storage densities can be achieved using this new method,” says 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 experts are considering using carbon sponges containing tiny pores. Substantial amounts of the palladium nanoparticles should fit inside these.

Journal Reference

1. D. Franz, U. Schröder, R. Shayduk, B. Arndt, H. Noei, V. Vonk, T. Michely, A. Stierle; Hydrogen Solubility and Atomic Structure of Graphene Supported Pd Nanoclusters; ACS Nano, 2021; DOI: 10.1021/acsnano.1c01997