From functional material to active components for energy storage and conversion

Energy storage and conversion are currently among the most relevant research topics, as the utilisation of renewable energy sources is fundamental to the implementation of CO2 reduction plans. Energy generation from wind and solar and the electrochemical storage of this energy in batteries or fuels such as hydrogen requires solutions that need to be improved in terms of both efficiency and scalability. Although some progress has already been made, in many cases the proposed concepts show good efficiencies in the laboratory, but they are not always easily scalable or too costly for larger scale production. Our long-term goal is to contribute to the development of solutions in the field of energy storage, on the one hand, by developing functional materials using (scalable) solid-state chemical synthesis and simple deposition techniques, and on the other hand, by building up basic scientific understanding in the field of structure-property relationships of energy storage materials, which will then lead to improved and more durable materials.

Active materials for photoelectrochemical energy storage in solar fuels

Oxide nitrides, for example, are very suitable materials for photoelectrochemical water splitting. The development of efficient photoelectrode materials is an important part of our work. In this context, a comprehensive characterisation is very important because structure, composition, crystallinity, porosity as well as transport properties influence the photoelectrochemical efficiency. The precise determination of these properties is necessary in order to understand and improve the activity of the functional materials depending on the synthesis methods. We have already achieved some success, on the one hand through detailed material understanding based on broad analytics (XRD, TEM, SEM, photoelectrochemical investigations) and on the other hand through further changes in the synthesis, such as better control of porosity or changing the charge carrier density through substitution. Furthermore, protective layers and co-catalysts are essential for a functioning photoelectrode. The task of developing active materials for photoelectrodes therefore includes the provision of suitable photocatalysts, including additives, and the development of scalable manufacturing processes, which in their entirety lead to a functioning component.

Conductive networks and electrode structure: Hybrid materials

Conductive networks play a very important role in energy storage systems. Li-ion batteries are a good example. In order to develop a high-performance electrode, not only the active material itself is important, but also the way in which an electrically conductive connection is established between the (usually insulating, oxidic) particles. We are therefore investigating how the electrode functions as a whole and not just the electrode material. An important question is how a conductive network can be formed between particles without negatively changing the properties of the active material, or even with the aim of improving them. The conductive network can consist of a large number of material classes and serve different length scales. Inorganic or ceramic bridges are often locally limited to the nanoscale, while layered systems such as reduced graphene oxide (RGO) or carbon nanotubes (CNTs) form long-range connections in the μm range. The synthesis and subsequent deposition of hybrid or composite materials is one of the routes we are pursuing to produce electrodes with conducting networks.

Functional materials for Li-ion batteries and beyond

We are investigating V-containing oxides for their suitability as insertion materials, such as Li+ or Na+. With the exchange of the ion to be intercalated, both the intercalation plateaus and the kinetics change. We are interested in understanding the differences in intercalation behaviour in order to develop better cathode materials for post-Li batteries. Comprehensive physical-chemical investigations are necessary to analyse the oxidation states and structural changes of the transition metal (compounds) depending on the state of charge of the battery and the battery type. At the same time, understanding the changes in the material during the charging and discharging process helps to better understand potential degradation processes.