Green hydrogen: Perovskite oxide catalysts analysed in an X-ray beam
Schematische Ansicht der transformierten Schicht (hellgrau) auf dem LaNiO3 Perowskitfilm (grün), aufgewachsen auf einem Substrat (braun). Rechts ist die vergrößerte Seitenansicht der transformierten Oxyhydroxid-Schicht (mit Spindichte an den Ni-Plätzen) aus Simulationen dargestellt. © UDE/AG Pentcheva
The production of green hydrogen requires catalysts that control the process of splitting water into oxygen and hydrogen. However, the structure of the catalyst changes under electrical tension, which also influences the catalytic activity. A team from the universities of Duisburg-Essen and Twente has investigated at BESSY II and elsewhere how the transformation of surfaces in perovskite oxide catalysts controls the activity of the oxygen evolution reaction.
In a climate-neutral energy system of the future, the sun and wind will be the main sources of electricity. Some of the "green" electricity can be used for the electrolytic splitting of water to produce "green" hydrogen. Hydrogen is an efficient energy storage medium and a valuable raw material for industry. Catalysts are used in electrolysis to accelerate the desired reaction and make the process more efficient. Different catalysts are used for hydrogen separation than for oxygen evolution, but both are necessary.
Perovskite oxide catalysts: inexpensive and with great potential
An interdisciplinary and international group of scientists from the University of Essen-Duisburg, the University of Twente, Forschungszentrum Jülich and HZB has now investigated the class of perovskite oxide catalysts for the oxygen evolution reaction in detail. Perovskite oxide catalysts have been significantly further developed in recent years, they are inexpensive and have the potential for further increases in catalytic efficiency. However, within a short time, changes appear on the surfaces of these materials which reduce the catalytic effect.
Spectroscopy at BESSY II
For this reason, the group has now analysed the surface structure in particular and compared the experimental data with density functional calculations. And spectroscopic analyses at the X-ray source BESSY II were performed. "We were able to determine that a certain surface facet is significantly more active and at the same time more stable than others. X-ray analyses allow us to understand how to overcome the traditional trade-off between activity and stability," says HZB scientist Dr Marcel Risch. The results also show how certain surface facets transform and where, for example, hydrogen atoms (or protons) accumulate.
These insights into transformation processes and structural transformations and chemical processes on the different facets of the samples studied are valuable: they contribute to the knowledge-based design of materials as electrocatalysts. After all, electrocatalysts are the key to many applications in green chemistry.
- Battery research with the HZB X-ray microscopeNew cathode materials are being developed to further increase the capacity of lithium batteries. Multilayer lithium-rich transition metal oxides (LRTMOs) offer particularly high energy density. However, their capacity decreases with each charging cycle due to structural and chemical changes. Using X-ray methods at BESSY II, teams from several Chinese research institutions have now investigated these changes for the first time with highest precision: at the unique X-ray microscope, they were able to observe morphological and structural developments on the nanometre scale and also clarify chemical changes.
- BESSY II: New procedure for better thermoplasticsBio-based thermoplastics are produced from renewable organic materials and can be recycled after use. Their resilience can be improved by blending bio-based thermoplastics with other thermoplastics. However, the interface between the materials in these blends sometimes requires enhancement to achieve optimal properties. A team from the Eindhoven University of Technology in the Netherlands has now investigated at BESSY II how a new process enables thermoplastic blends with a high interfacial strength to be made from two base materials: Images taken at the new nano station of the IRIS beamline showed that nanocrystalline layers form during the process, which increase material performance.
- Hydrogen: Breakthrough in alkaline membrane electrolysersA team from the Technical University of Berlin, HZB, IMTEK (University of Freiburg) and Siemens Energy has developed a highly efficient alkaline membrane electrolyser that approaches the performance of established PEM electrolysers. What makes this achievement remarkable is the use of inexpensive nickel compounds for the anode catalyst, replacing costly and rare iridium. At BESSY II, the team was able to elucidate the catalytic processes in detail using operando measurements, and a theory team (USA, Singapore) provided a consistent molecular description. In Freiburg, prototype cells were built using a new coating process and tested in operation. The results have been published in the prestigious journal Nature Catalysis.