Synchrotron research for climate protection and energy transition

"When chemical energy is converted into electrical energy in batteries, these complicated processes can be followed with synchrotron radiation. This research has helped refining lithium-ion batteries that are standard today. Through better understanding, their energy density, lifetime and safety are still being increased. But we are thinking even further into the future, and synchrotron radiation is indispensable for the resarch on lithium free battery materials which are much more sustainable, e.g. sodium, potassium and aluminium," says Prof. Dr. Helmut Ehrenberg (KIT).

Solar cells made of semiconductor materials are the basis of electricity generation from solar energy. Mostly silicon is used for this, but there are alternatives and supplementary possibilities. Perovskite solar cells, whose functioning is being researched at the Helmholtz-Zentrum Berlin (HZB) with synchrotron radiation, are particularly promising. They have the advantage that they can be produced cheaply and utilise different wavelengths than silicon. In so-called tandem solar cells, which combine both semiconductors, a higher efficiency can therefore be achieved than in conventional modules. Synchrotron radiation is used to research the properties of perovskite solar cells, for example the temperature-structure relationship, the process of crystallisation or the stabilising effect of fluorine additives in lead-free perovskite solar cells. But the silicon layer in the tandem solar cell can also be made even more effective through targeted nanotexturing.

The Helmholtz Innovation Lab HySPRINT is a cooperation platform for industry at HZB with a focus on (opto)electronic materials and devices at an early stage of technological development. Tandem solar cells are developed and optimised here. The efficiency of the perovskite tandem solar cell on a laboratory scale was almost 30% at the end of 2021. Since then, further research progress has been achieved: the use of standard silicon solar cells and silicon bottom cells from the company Q CELLS that are ready for series production.

 © Shearing et al./ Nature Communications

The use of renewable energy also includes its storage. There are different concepts depending on the application. Batteries have high efficiencies and can be used in mobile applications, which is why intensive research is being carried out on the entire value chain - from the functional mechanism and new materials to durability, safety and sustainability. Synchrotron radiation, for example, can be used to distinguish the role of individual elements in order to find customised solutions. Researchers all over Germany are investigating batteries and their materials with synchrotron radiation. University research and application go hand in hand.

© BMBF

Research networks play an important role in battery research. At European level, there is the EU project "BIG-MAP" (Battery Interface Genome - Materials Acceleration Platform) part of the large-scale research initiative Battery 2030+ for the development of sustainable batteries for the future, in which the European Synchrotron Radiation Facility (ESRF) is involved. Battery research is also being driven forward there in the "Grenoble Battery Hub". In the Cluster of Excellence POLiS of the Karlsruhe Institute of Technology (KIT) and the University of Ulm and other partners, future batteries are being researched that are more powerful, more reliable, more sustainable and more environmentally friendly than the current lithium-ion batteries. Synchrotron radiation is used to understand how the batteries work and adapt them accordingly. Synchrotron radiation is also used in other competence clusters of the BMBF umbrella concept "Research Factory Battery", for example in FestBatt and ExcellBattMat.

Great expectations are being placed in the industrial use of green hydrogen, for example in steel production or in aviation. "Green" is the term used to describe hydrogen that has been produced in a CO₂-neutral way - either with green electricity or, in future, directly through photolysis in "artificial leaves". In this process, tailor-made catalysts are to make it possible to split water with the help of sunlight. Research with synchrotron radiation not only helps to find particularly suitable catalyst materials, but also to develop especially efficient structures or combinations of materials and to understand processes and investigate them during operation. Molecular films, such as those made possible by the European XFEL, can also contribute to this.

Basic research on catalysis is currently bundled, for example, in the priority programme SPP2080 "Catalysts and Reactors under Dynamic Operating Conditions for Energy Storage and Conversion", in which research is being conducted, among other things, on reactivating catalysts in quiescent phases and increasing the yield of desired reaction products. Many groups in SPP2080 use synchrotron radiation, as does KIT's DFG Collaborative Research Centre "TrackAct - Tracking Active Centres in Heterogeneous Catalysts for Emission Control". A bridge to industry is to be built by the new "CatLab" research platform for catalysis in Berlin Adlershof. Here, chemical conversion processes based on novel tailor-made (chemo, electro and photo) catalysts are developed on an industrial scale.

There are also various approaches to storing hydrogen. Besides the usual compressed gas storage, hydrogen can also be chemically bound in methanol or liquid organic hydrogen carriers (LOHC) or stored in solids, especially in metal hydrides and adsorptively in nanostructured materials. Their structure and functioning are studied at synchrotrons, e.g. the adsorption and release to graphene-supported Pd nanoclusters or the storage in a hydride composite system.

A centre for synchrotron research on the fundamentals of the use of hydrogen is being built in northern Germany in two new institutes on the DESY campus. Here, both the DESY light sources and the X-ray laser European XFEL are in the immediate vicinity. These are the Centre for Molecular Water Science (CMWS) with the participation of a large number of European partners and the Center for X-ray and Nano Science (CXNS) as a cooperation between DESY, Helmholtz Centre Hereon and Christian-Albrechts-Universität zu Kiel (CAU).

Research with synchrotron radiation also contributes to the understanding of our environment, e.g. how climate-relevant aerosols behave in the atmosphere, what basic properties water or gas hydrates have, which substances react with each other in the soil, which soils or rock formations can absorb CO₂ or what part the subduction of rocks has in the global carbon cycle.

© ESRF

At the European Synchrotron Research Facility (ESRF) in Grenoble, France, the "Geobridge" working group conducts research on such topics, but other research areas there are also dedicated to climate change.

"Today, the chemical industry still uses almost entirely fossil raw materials for the production of chemical products. Converting this to renewable ones is a major challenge. Synchrotron radiation is a unique key to this, because it allows us to observe how the catalysts needed for this work - "operando" in technical jargon. Only in this way can materials be developed in a targeted and efficient way and create a basis for computer-aided design," says Prof. Jan-Dierk Grunwaldt, KFS chairman and himself involved in the conversion of wind and solar energy or biomass into chemical products.