Researchers led by Andreas Stierle at Deutsches Elektronen-Synchrotron (DESY) have laid the foundations for an alternative method for storing hydrogen, using iridium-seeded palladium nanocluster superlattices with 1.2 nanometer cluster diameters. The team, which also includes researchers from the Universities of Cologne and Hamburg, published its findings in the journal ACS Nano.

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. That’s why we are trying palladium particles that are only about one nanometer across.

—Andreas Stierle

To ensure that the tiny particles 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.

The palladium nanoparticles (green) are stabilized by a core of iridium (red). Hydrogen can accumulate on their surface and can be released again by heating. Credit: DESY, Andreas Stierle

Attaching the palladium particles to the graphene at intervals of just two and a half nanometers results in a regular, periodic structure, said Stierle, who is the head of the DESY NanoLab.

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 inside.

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 surface of the particles, because the gas molecules don’t have to push their way out from inside the cluster.

The researchers want to find out what storage densities can be achieved using this new method, said Stierle. 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. Substantial amounts of the palladium nanoparticles should fit inside these.

Resources

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