Efficient collection and storage of renewable forms of energy like solar radiation or wind requires the development of advanced functional materials. CMSP research in the field of sustainable energy focuses on this materials-related aspect. Using modern computer simulation techniques, conversion and storage processes are investigated on the atomic scale. The research topics include nanostructured solar cells, battery materials, and photocatalytic water splitting.
Hydrogen gas is an important chemical feedstock for the synthesis of many materials. It can also be used as energy carrier and for energy storage. Thus, the efficient production of oxygen and hydrogen by splitting water molecules is a key process in the quest for sustainable energy sources. Using computer modeling, we are simulating how this reaction takes place on hematite (Fe_2O_3) surfaces. Many properties of this material make it very appealing as anode in photo-electrochemical water splitting reactions, but major aspects of this process remain to be understood.
In dye sensitized solar cells (DSSCs) light is absorbed by molecules (dyes), which are attached to the surface of wide-bandgap semiconductors. For the paradigmatic case of organic molecules on TiO_2 surfaces, we are investigating the interactions of the dyes with the surface, the electronic structure and excited electronic states. Such information, obtained from calculations based on density-functional theory, can help to better understand the stability of DSSCs and the efficiency of the electron transfer, which is at the heart of the functioning of such solar cells.
One of the current challenges for researchers in renewable energy is to find a way to use solar energy to produce fuels, like hydrogen and hydrocarbons, from water and carbon dioxide. This would make the energy cycle carbon-neutral, while retaining the advantage of using liquid and gaseous fuels. We investigate by density functional theory why some titanium-based photocatalysts are more active than pure titania for these reactions. The systems considered are comprised of black hydrogenated titania, sodium titanate and copper clusters at titania surfaces.
The desire to employ intermittent renewable energy sources to produce electricity, as well as the spread of electric vehicles, will increase the importance of electricity storage. Metal-air batteries are particularly interesting for their high energy density, but high overpotentials mean that losses upon charging and discharging are limiting their practicality. To solve this issue, we work to understand the basic electrochemical reactions taking place in these batteries during formation and dissolution of oxides of lithium and sodium, as well as in the presence of electrocatalysts such as MnO_2. Computer simulations using density functional theory are our main tool.
Catalysts are an important ingredient for many reactions and thus for many applications, but they are often not very active and can be very expensive. In order to overcome these limitations, it is necessary to understand their working mechanisms and to create catalytic systems with a high degree of effectiveness. To this end, we are investigating molecules, called phtalocyanines, which are related to heme molecules critical in blood. The center of these active catalysts consists of a single atom, which allows high-precision studies of the reaction mechanisms.