What does the MPI CEC do?
Politicians, enterprises, scientists and citizens agree that a global energy change is necessary. The objective lies in arriving at a form of energy management, which is sustainable, environmentally friendly and cost-efficient. In the realization of this long-term goal, general questions about basic research in the field of chemistry are affected, apart from a large number of political and technical problems. These questions are concerned in the first instance with the generation, storage and transport of energy.
Sunlight is the solution
Nature provides the best example for highly efficient use of energy. Nature's energy transformation processes lead to a high level of efficiency in the storage of solar energy in chemical bonds. All energy used in nature by humans, animals and plants stems ultimately from sunlight. In fact, the sun radiates sufficient energy onto Earth in each single hour to cover global energy demand for the whole year. Naturally it is impossible to use all this energy. The figure however illustrates that even just a fraction of the solar energy available is enough to implement future energy management. The challenge lies in putting into practice the chemistry on which it is based in an efficient form and on a global scale. This will require a concerted effort from scientists, engineers and politicians.
Nature as model
In nature, energy is stored by means of the highly complicated process of photosynthesis in the form of energy-rich molecules, e.g. sugars. The energy stored in the molecules is used by organisms specifically to maintain life processes or produce biomass. The chemical processes taking place in nature are a model for energy research since they unite the highest possible efficiency and sustainability as well as taking care of the environment. Through photosynthesis, carbon dioxide (CO2) and water (H2O) are transformed into useful organic molecules such as sugar, for example, and oxygen (O2). The waste products generated in the process, such as O2, are "disposed of" in the atmosphere.
The second base material required for this unique type of chemistry is water, i.e. H2O. This is available on Earth in practically inexhaustible quantities.
Unfortunately, it is not possible to recreate photosynthesis chemically in a test tube using synthetic chemistry. The molecules involved are much too complex for this and also too sensitive. Nature too, must continuously deploy highly complicated repair mechanisms in order to maintain the photosynthesis process.
Basic chemical research in the area of energy research must therefore be concerned with understanding in detail fundamental energy-generating chemical reactions. A particularly important role must be accorded to understanding catalysts, i.e. those substances which first permit individual reactions to take place without themselves being consumed in the reaction process. In nature these are enzymes, in the laboratory mostly chemical compounds containing metals. The natural processes serve as a source of inspiration.
Storing solar energy: Impossible without a catalyst
The storage of primary solar energy in the form of chemical bonds holds a large number of advantages, in particular the possibility to harmonize the solar energy which occurs at irregular intervals depending on location, time of day, season or degree of cloud with energy consumption requirements. In turn, energy consumption fluctuates depending on people's living habits and depends therefore in the first instance on time of day and season. Catalytic systems to implement these reactions have seen a rapid development in the recent past. It is of key importance that attention is paid in this development process to process sustainability. This means that substances used in the catalysts must exist in sufficient volumes on Earth and also be accessible in order to be able to carry out the processes on a global scale. According to all currently existing know-how, these catalysts will have to contain metal ions. In practice this means that certain metals are especially significant since only these are available in sufficient quantities on Earth. These are above all the metals in the first transition series of the Periodic Table of the Elements.
Nature has chosen precisely this approach: all energy-preserving reactions in nature are based on exactly these metals. The chemistry of these metals is however particularly complex due to their special bonding properties, so that state-of-the-art theoretical and analytical methods must be deployed to explain their reaction mechanisms.
The MPI CEC's Mission
The MPI for Chemical Energy Conversion sees it as its task to investigate fundamental chemical processes in energy transformation and thus to contribute to the development of new and efficient catalysts. Our approach to this problem is based on a profound understanding of the underlying chemical reactions. Only when we know in detail how the reaction mechanism looks – and above all how the catalyst is involved in it – we can develop improved and sustainable catalysts on a rational basis. For as Max Planck once said: "Insight must precede application."
Multidisciplinary research will be essential to achieve this goal. At the MPI CEC the fields of heterogeneous catalysis, molecular catalysis and inorganic spectroscopy are being explored in combination using state-of-the art experimental and theoretical analysis methods. We are convinced that this combination is the key to understanding and ultimately to controlling fundamental chemical processes.
Challenges for the research field of chemical energy conversion
Whether electrically powered cars, hydrogen storage or fuel cells: The challenges in the field of chemical energy conversion are manifold. The following list provides a short overview of some of the chemical reactions involved which need to be explored in greater depth.
(1) Transforming light into electrical energy
Primary energy is light energy. This energy must be gathered and converted into electrical energy. Significant advancements in the area of photovoltaic have already been achieved, but further progress is necessary.
(2) Hydrogen for energy storage
Since electrical energy cannot be stored and transported in a satisfactory way, it is necessary to store it in the form of chemical bonds. The production of hydrogen from protons and electrons plays a central role here. We are convinced that this hydrogen, which is primarily produced photochemically, must play a key role in future energy management.
(3) Storage materials for hydrogen
The photochemically produced hydrogen can be stored. This is known to be a difficult venture, since the hydrogen molecule is present in the form of a very small, volatile gas, which does not allow itself to be easily stored. The development of suitable storage materials is an important research venture.
(4) Catalytic water splitting
The electrons required for hydrogen production are obtained from oxidation processes. Ideally, the electrons stem from oxidation of water. Oxygen, electrons and protons are produced in the reaction. Although the electrochemical splitting of water has indeed been known for a long time, it is however too inefficient for use on a large technical scale. Catalytic systems for the oxidation of water are at the focus of modern energy research.
(5) Further development of fuel cells
The energy stored in the photochemically produced hydrogen can be made usable again in a fuel cell. The development of more efficient fuel cells is a further important research field.
(6) Small molecules for hydrogen storage
Alternatively, the photochemically generated hydrogen can be converted directly together with other molecules into energy-storage substances, whereby a particularly positive aspect is the activation of carbon dioxide in order to arrive at organic acids or alcohols. Methanol (CH3OH), for example, is thus an attractive energy carrier since it exists in liquid form and displays a high energy density. Another option is to convert atmospheric nitrogen into ammonia (NH3). In both cases suitable catalytic systems are necessary. Both offer the advantage that existing pipelines and infrastructures can be used for their transport.
Further literature on this topic
"Energie.Wende.Jetzt - Eckpunkte für eine zukünftige Energieversorgung", R. Schlögl 04/2019
"Ein Enzym, das die Welt veränderte", T. Lohmiller, N. Cox und W. Lubitz in Labor&more 08/2015 Link
"Wie Pflanzen Wasser spalten", Spektrum der Wissenschaft September 2013 Link
"Vorratshaltung für Energie", Ferdi Schüth in Spektrum Spezial 3/2011. Link
"Herausforderung Energie", Jürgen Renn, Robert Schlögl and Hans-Peter Zenner (ed.) 2011 Link