What are you researching right now, Mr Bäumer?

Dr. Christoph Bäumer investigates catalysts for the electrolysis of water. These are materials that can accelerate the splitting of water into hydrogen and oxygen, thus contributing to the efficient storage of renewable electrical energy. He uses the Oxide Cluster at the Peter Grünberg Institute (PGI-7) for this purpose. Headed by Prof. Regina Dittmann, researchers produce and investigate special materials at the facility that serve as model systems for applications in information technology and for energy storage. The materials are wafer-thin layers of compounds containing oxygen (oxides). These often have special electronic properties. Because impurities from the ambient air can change the surface of the thin layers, all processes at the facility must take place in an ultra-high vacuum. The pressure here is more than 10 billion times lower than the ambient pressure.

For their model systems, the researchers need layers with as precisely defined a structure as possible. To do this, they irradiate the raw material with pulsed laser radiation. The material is heated to such an extent that a plasma is formed – a special particle mixture (light blue spot in the photo), which is deposited as a thin layer on the surface of a carrier material. This method produces a wafer-thin layer with an ordered crystal structure and a low number of defects. In addition, surfaces can be made with precision down to individual atomic layers.

The samples are transported to another part of the facility for further analysis using a steel tube under a vacuum. For this, a transfer arm slides a sample into a magnetic transport carriage, which then brings the sample to the next station.

Using photoelectron spectroscopy, researchers determine the electronic and chemical properties of the sample surface. These properties are decisive for the catalytic activity. The sample (at the bottom of the picture, on the silver shining sample plate) is illuminated with X-rays (with the silver component at the top right of the picture). The X-rays generate electrons characteristic for the sample – so-called photoelectrons. These are recorded by an analyser (copper-coloured component at the top left of the picture). Their energy and intensity allow conclusions to be drawn about the atomic composition of the sample surface.

Using the atomic force microscope, researchers can measure the atomic structure of the sample surface, which can also be important for catalytic activity. To achieve this, a fine tip at the end of a cantilever (centre of the picture, above the gold-coloured plate) moves over the sample surface. The deflection of the cantilever allows the surface texture to be shown.

To investigate the catalytic properties of the material, Christoph Bäumer transfers the sample from the ultra-high vacuum of the facility into a glove box with a protective gas atmosphere. As one of three “electrodes”, it is placed in an aqueous electrolyte solution and a voltage is applied. With sufficient voltage, the water is split into hydrogen and oxygen. The researchers measure the performance of the sample electrode, thus determining its catalytic properties in order to correlate them with the previously determined properties of the sample surface. Based on this, the researchers hope to gain insights into the structure-property relationships in order to develop catalysts that are as efficient as possible.