Water is the most common solvent used for most chemical reactions. In addition, organic solvents such as N.N-dimethylformamide, acetonitrile or dichloromethane are used - despite their toxicity, flammability and volatility. However, not all substances (metal salts) can be dissolved in water or in organic solvents and not all reactions can take place in them. Furthermore, many metals cannot be separated from these media.
Since the late 1990s, chemists' attention has been drawn to a new type of solvent: ionic liquids. They are salts that are liquid at relatively low temperatures. Usually they have negligible vapor pressure, so they do not vaporize at normal temperatures and pressures. They are generally non-flammable and in some cases stable up to about 400°C and are non-toxic. They have a wide electrochemical potential window of about 3 to 4 V, while that of aqueous systems is less than 2 V. This allows the electrochemical deposition of more metals than from aqueous or organic solutions.
Today, ionic liquids are used not only in electrochemistry but also in biochemistry, organic and inorganic chemistry, and materials science.
Wherever electric charges have to overcome phase boundaries, electrochemistry plays a central role. We investigate the mechanisms of such processes and use them to develop strategies for designing economical and sustainable processes. One example with high industrial relevance is electrochemical surface engineering, where electrochemical processes such as electrodeposition or anodization are used to anneal surfaces (e.g. for corrosion and wear protection) or to produce novel functional materials (e.g. composite materials).
Efficient and scalable electrochemical energy storage systems are needed, among other things, to ensure an environmentally friendly energy supply. Furthermore, they are the cornerstone for sustainable electromobility.
Our research activities in the field of energy storage aim at the following aspects:
Production of hydrogen by electrolysis
The industrial production of hydrogen using renewable energy sources represents an important milestone on the way to a CO2-neutral economy and mobility. This requires the further development of robust and scalable electrolysis processes, in particular membrane-based processes such as PEM (polymer electrolyte membrane) and AEM (alkaline anion-exchange membranes). Our research in this area focuses on the development of corrosion-resistant materials for electrolyzer components, low-cost catalysts and the optimization of flow conditions in the electrolysis cell.
Improving energy and power density through targeted material optimization and synthesis of novel structures.
Improved performance of battery materials is achieved through various processes, including nanosynthesis, nanostructuring, surface modification of active materials, and new opportunities for transition metal substitution in cathode materials. The selection of high-energy active materials and the study of their structural properties are important for performance improvement. Our materials research includes metal-substituted NMC, LMNO spinels, silicon and TiO2 based anode materials, among others.
Improving safety with new electrolytes and studying degradation mechanisms in Li-ion batteries.
Activities towards safety include the development of new electrolytes and additives for minimizing safety issues. Specific aspects to improve battery safety are non-flammable electrolytes (e.g. ionic liquids), electrolytes modified by additives and investigation of the influence of water contamination.
Application of novel analytical methods
To study our materials and the electrolyte-electrode interfaces, important analytical methods such as atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, electrochemical dilatometry, and impedance spectroscopy, among others, are in use.
The production of hydrogen could become an important component for future energy supply. There are various ways to produce hydrogen. Currently, hydrogen is mainly produced via classical methods such as steam reforming of natural gas, water electrolysis and chemical dehydrogenation. Photoelectrochemical water splitting is another environmentally friendly method of producing hydrogen via a photoelectrode. Here, sunlight is directly used through a semiconductor electrode for solar water splitting.
Photoelectrochemistry combines the fields of semiconductor physics, electrochemistry and materials science. The main requirements for the semiconductor electrode are:
- Good light absorption in the visible range
- Position of the band edges to the water redox potential
- High photoelectrochemical stability
- Efficient charge transfer
- Catalytic activity
- Low cost
In our department we research materials for photoelectrochemical hydrogen production. On the one hand, we investigate classical semiconductor materials, such as silicon and III-V semiconductors, and on the other hand we deal with the fabrication of porous Cu2O semiconductor electrodes. The focus of our research is on material stability, kinetics at the interface between semiconductor and electrolyte, catalytic effects, charge transport and optical parameters of the semiconductor.
Compounds such as polyaniline (PAni), polypyrrole (PPy) or poly(3,4-ethylenedioxythiophene) (PEDOT) belong to the intrinsically conductive polymers. They have several oxidation states whose properties (e.g., color, band gap, conductivity, or volume) differ from each other. Possible applications of these polymers are antistatic coatings or electrode materials in sensors.
By incorporating inorganic materials (e.g., nanoscale metal particles), hybrid materials are obtained that often advantageously combine the properties of both components. We pursue this approach mainly with respect to sensory and catalytic applications.ise semiconductor materials, such as silicon and III-V semiconductors, and on the other hand we are engaged in the fabrication of porous Cu2O semiconductor electrodes. The focus of our research is on material stability, kinetics at the interface between semiconductor and electrolyte, catalytic effects, charge transport and optical parameters of the semiconductor.