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Proposing Institution

Lehrstuhl für Theoretische Chemie,TUM
Project Manager

Yonghyuk Lee
Lichtenbergstr. 4
85747 Garching
The electrolysis of liquid water to hydrogen fuel provides an attractive process for the conversion of electricity generated by solar and wind power to chemical energy. A major challenge in this conversion process is the rate limiting step of the oxygen evolution reaction (OER). The development of active OER catalysts, therefore, is in the center of academic as well as industrial research. Only few solid materials are known as being stable at the harsh acidic operating conditions of proton exchange membrane (PEM) cells. Iridium oxide (IrO2) is perhaps the only pure metal oxide material which is sufficiently stable and active to promote OER kinetics. Due to its open rutile structure, many undercoordinated atoms are present at the surface, providing potential catalytically active reaction sites. Despite of these favorable physical and chemical properties as OER catalyst, there is an important limitation to commercialize iridium based PEM stacks as iridium is one of the rarest elements with an abundance of about 0.08ppb in Earth’s crust. Thus, lowering the price of IrO2-based catalysts while maintaining or even improving the OER activity is a key challenge for future applications on an industrial scale.A common approach to reduce the content of iridium is to exploit the property of IrO2 to form “solid solutions” with other transition metal oxides that crystallize in rutile structures such as ruthenium, manganese and titanium oxide. Preceding experimental work demonstrated that IrO2 may be “diluted” by cheaper materials, either as a solid solution or core-shell structure, without sacrificing desirable properties including electric conductivity and catalytic activity. Core-shell catalysts have been widely investigated due to their high efficiency and flexibility to tune their morphology. In order to build core-shell heterostructures, it is indispensable to minimize the lattice mismatch at the interface which causes strain effects and potentially physical instability of a material. Rutile ox- ides have considerable advantage in this point since the highly oxidized metal ions (4+) are relatively small for most elements, hence limiting the lattice mismatch between many rutile oxides. However, it is still unknown how the presence of different elements in typically nanostructured catalysts affect electronic structure, surface ener- gies and corresponding Gibbs free energies of adsorption for the reactants in the OER. In the proposed project, IrO2-based core-shell and mixed oxide heterostructures with other cheap rutile oxides such as manganese oxide (MnO2), tin oxide (SnO2) and titanium oxide (TiO2) will be systematically investigated by first-principles simulations. Based on density-functional theory (DFT), electronic and structural properties of bulk and surface atoms in mixed oxide catalysts will be investigated. Realistic nanoparticle structures at operating conditions will be derived from computed surface free energies and the Wulff theorem to construct atomistic models of nanocrystals. DFT calculations for slab models will be performed using the numeric atom-centered basis functions as implemented in full-potential FHI-AIMS code. Ab initio molecular dynamics will carry out simulations of nanoparticles by using Gaussian and plain waves approaches in CP2K code. The results of the proposed research project will be disseminated via the Kopernikus/P2X consortium to collaborators from experimentalist groups and industrial partners. The research will therefore be of direct relevance to streamline ongoing research efforts towards the design of novel catalysts for commercially viable PEM stacks. In order to promote the perception of first-principles simulations and to develop a better understanding of the resulting atomistic models for a broader audience including experimentalist and industrial partners I will collaborate with the virtual reality team (Dr. Ruben García-Hernández) at the Leibniz Supercomputing Centre.

Impressum, Conny Wendler