Prof. Dr. Christian Liebscher from the Research Center Future Energy Materials and Systems is investigating how metal powders can safely store green hydrogen at room temperature and low pressure.

Green hydrogen is said to be a key to the energy transition. Storing it safely is the aim of the project “GreenH2Metals: Sustainable and recyclable metal alloys for the efficient and safe storage of hydrogen for stationary applications”, in which Ruhr University Bochum is involved with two sub-projects. The Bochum working group is investigating the micro- and nanostructure of metal alloys that can absorb and release hydrogen. The raw materials for this should come from secondary sources, i.e. be recycled and also be able to be recycled. The project is being funded by the Federal Ministry of Education and Research with around 3.3 million euros, 750,000 euros of which will go to the Ruhr University.

Disadvantages of gas and liquid storage
If green hydrogen can one day be produced on a large scale using wind or solar power, for example, it will also have to be stored. This is the only way it can be used when it is needed. “Storage in gas or liquid tanks, which has been the norm up to now, has various disadvantages,” explains Prof. Dr. Christian Liebscher from the Research Center Future Energy Materials and Systems. “The hydrogen either has to be highly compressed or extremely cooled, which requires a lot of energy. In addition, thermal insulation is a problem with liquid storage, resulting in losses. There is also the risk of hydrogen escaping very quickly due to leaks, which is associated with the risk of an explosion.”

Safe and loss-free storage
The type of storage being investigated by the project team does not have either of these disadvantages: powder particles or pellets pressed from powder made from an alloy of titanium and iron are able to absorb hydrogen at moderate pressures of less than 40 bar. The hydrogen molecules are first split on the surface of the particles. The atoms then diffuse into the metal lattice. This turns the metal into a so-called hydride. If the pressure around the particles or pellets is lowered again, the hydrogen escapes again. The whole process works at room temperature and is virtually loss-free. If a tank were to burst, the hydrogen would only escape very slowly, greatly reducing the risk of explosion.

The working group at Ruhr University Bochum is working on two sub-projects to analyze the micro- and nanostructure of the storage material in collaboration with the Max Planck Institute for Sustainable Materials in Düsseldorf. “For example, we want to know how the material structure develops when we use raw materials from secondary sources, i.e. from recycling,” explains Christian Liebscher. “They could contain impurities, which could even have a positive effect on the storage properties in some cases.” Using transmission emission microscopy and atom probe tomography, the researchers want to investigate in detail how the alloy behaves during loading and unloading and whether there are any wear effects, for example. “Ideally, we also want to optimize the storage properties in this way,” says Christian Liebscher.

Cooperation partners
The project is being coordinated by Helmholtz-Zentrum hereon GmbH. In addition to the Ruhr University Bochum, the RWTH Aachen University and the Federal Institute for Materials Research and Testing are also involved.