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.
- Susanne Nies appointed to EU advisory group on Green DealDr. Susanne Nies heads the Green Deal Ukraina project at HZB, which aims to support the development of a sustainable energy system in Ukraine. The energy expert has now also been appointed to the European Commission's scientific advisory group to comment on regulatory burdens in connection with the net-zero target (DG GROW).
- The future of corals – what X-rays can tell usThis summer, it was all over the media. Driven by the climate crisis, the oceans have now also passed a critical point, the absorption of CO2 is making the oceans increasingly acidic. The shells of certain sea snails are already showing the first signs of damage. But also the skeleton structures of coral reefs are deteriorating in more acidic conditions. This is especially concerning given that corals are already suffering from marine heatwaves and pollution, which are leading to bleaching and finally to the death of entire reefs worldwide. But how exactly does ocean acidification affect reef structures?
Prof. Dr. Tali Mass, a marine biologist from the University of Haifa, Israel, is an expert on stony corals. Together with Prof. Dr. Paul Zaslansky, X-ray imaging expert from Charité Berlin, she investigated at BESSY II the skeleton formation in baby corals, raised under different pH conditions. Antonia Rötger spoke online with the two experts about the results of their recent study and the future of coral reefs.
- Long-term stability for perovskite solar cells: a big step forwardPerovskite solar cells are inexpensive to produce and generate a high amount of electric power per surface area. However, they are not yet stable enough, losing efficiency more rapidly than the silicon market standard. Now, an international team led by Prof. Dr. Antonio Abate has dramatically increased their stability by applying a novel coating to the interface between the surface of the perovskite and the top contact layer. This has even boosted efficiency to almost 27%, which represents the state-of-the-art. After 1,200 hours of continuous operation under standard illumination, no decrease in efficiency was observed. The study involved research teams from China, Italy, Switzerland and Germany and has been published in Nature Photonics.