The PhD will be carried out at the DLR Institute for Future Fuels in Cologne as part of EU co-funded research projects. The candidate will be part of an interdisciplinary, multinational research team of chemical and materials engineers and will have access to state-of-the-art chemical and ceramic processing laboratories and a broad infrastructure of analytical and structural characterisation tools available at the DLR facility in Cologne-Porz-Wahn. The doctorate is awarded by RWTH Aachen University as part of the Chair of Solar Fuels in the Faculty of Mechanical Engineering, which was established jointly with DLR.

In the broader environmental, societal and political framework of a carbon-neutral future energy mix, there is an urgent need for the use of renewable energy (RE) for electricity generation as well as for carbon-free industrial process heat. One approach to decarbonising industrial process heat is so-called 'electrification', based on RE resources; however, these are unsteady, so effective ways of storing RE in the form of heat need to be developed in parallel to ensure 24/7 operation. The high-temperature regenerative heat storage and recovery systems currently used in industry consist of porous ceramic media that are "charged", i.e. heated, with hot process exhaust gases. In addition, several oxide systems are capable of (endothermic) thermal reduction and reversible exothermic oxidation in an air atmosphere, which is accompanied by considerable heat effects and can thus significantly increase the storage density. Current work at DLR has already shown that storage devices made of low-cost, environmentally friendly perovskite materials can not only enable cyclic, reversible charge/discharge operation, but can also be formed into stable porous ceramic structures. These properties and the ability to utilise gas flows under high pressure and without significant pressure drop make the specific approach fully compatible with the "modularity" and thus easy scalability of commercial regenerative heat storage/recovery systems, which can thus be transformed into hybrid thermochemical heat storage/heat exchangers. For an envisaged commercialisation of such concepts, it is necessary to develop a scalable process for the fabrication of such porous solid structures through a rational design from the molecular level upwards and to validate their reliable operation through long-term cycling tests.

In this context and perspective, the main goals and tasks of the dissertation are the following:

• Synthesis of multicomponent perovskite materials with scalable solid-state techniques in powder form, as well as their characterisation in terms of critical properties (e.g. particle size, phase composition, specific surface area, micromorphology, etc.).
• Screening and optimisation of such perovskite compositions with respect to specific properties in TGA/DSC test rigs coupled with the necessary monitoring, control and gas outflow analysis systems.
• Fabrication of small- and larger-scale perovskite porous ceramic structures - reticulated porous ceramics, also known as "ceramic foams", honeycombs, 3D printed objects.
• Measurement of application-relevant properties (e.g. thermal conductivity, heat capacity, porosity, mechanical strength, coefficient of thermal expansion, permeability, etc.).
• Evaluation of such porous structures with regard to long-term, cyclic reduction-oxidation operation in special reactor test rigs.
• Development and validation of chemical kinetics models for powders and porous structures.
• Modelling and simulation of thermochemical stresses to quantify the chemical/thermal contributions to dimensional changes, their reversibility and the critical chemical/thermal stresses as a function of perovskite composition.