The innovative energy carrier of the future

Iridium stabilized palladium nanoparticles

The palladium nanoparticles (green) are stabilized by a core of iridium (red). Hydrogen can accumulate on their surface as a kind of chocolate icing – and can be released again when heated. Credit: DESY, Andreas Stierle

An innovative approach could turn nanoparticles into simple reservoirs for storing hydrogen. The highly volatile gas is considered to be a promising energy carrier for the future, which can supply climate-friendly fuels to, for example, aircraft, ships and trucks as well as allow climate-friendly steel and cement production – depending on how the hydrogen gas is generated. However, it is expensive to store hydrogen: Either the gas must be stored in pressure vessels of up to 700 bar, or it must be liquefied, which means that it is cooled down to minus 253 degrees. Celsius. Both procedures use extra energy.

A team led by DESYAndreas Stierle has laid the foundation for an alternative method: to store hydrogen in tiny nanoparticles made of the precious metal palladium, only 1.2 nanometers in diameter. That palladium can absorb hydrogen like a fungus has been known for some time. “But until now, it’s been a problem getting the hydrogen out of the material again,” Stierle explains. “That’s why we try palladium particles that are only about a nanometer across.” A nanometer is one millionth of a millimeter.

To ensure that the tiny particles are sufficiently robust, they are stabilized by a core made of the rare precious metal iridium. In addition, they are linked to one graph support, an extremely thin layer of carbon. “We are able to attach the palladium particles to the graph at intervals of only two and a half nanometers,” reports Stierle, head of DESY NanoLab. “This results in a regular, periodic structure.” The team, which also includes researchers from the universities of Cologne and Hamburg, published its findings in the journal American Chemical Society (ACS). ACS Nano.

DESY’s X-ray source PETRA III was used to observe what happens when the palladium particles come in contact with hydrogen: essentially, the hydrogen adheres to the surfaces of the nanoparticles, and almost none of it penetrates. The nanoparticles can be depicted as resembling chocolate: an iridium nut in the center, wrapped in a layer of palladium instead of marzipan, and the chocolate coated on the outside of the hydrogen. All that is needed to recover the stored hydrogen is to add a small amount of heat; the hydrogen is released quickly from the surface of the particles because the gas molecules do not have to squeeze out from inside the cluster.

“Next, we’ll find out what stock densities can be achieved using this new method,” says Stierle. However, some challenges still need to be overcome before moving on to practical applications. For example, other types of carbon structures may be a more suitable carrier than graphene – experts are considering using carbon sponges that contain tiny pores. Significant amounts of the palladium nanoparticles should fit into these.

Reference: “Hydrogen Solubility and Atomic Structure of Graphene Supported Pd Nanoclusters” by Dirk Franz, Ulrike Schröder, Roman Shayduk, Björn Arndt, Heshmat Noei, Vedran Vonk, Thomas Michely and Andreas Stierle, 11 October 2021, ACS Nano.
DOI: 10.1021 / acsnano.1c01997

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