On the way to new materials for energy conversion

The cluster of excellence e-conversion is happy to announce that three new Hans Fischer Senior Fellows at TUM Institute of Advanced Study (IAS) will be joining our community for the next three years! Professor Laura Herz from the University of Oxford will be guest with Professor Thomas Bein at Ludwig-Maxmilians-Universität (LMU) München and Professor David Egger at Technische Universität München (TUM). The second fellow will be Professor Ib Chorkendorff from the Technical University of Denmark. His hosts will be Professor Ulrich Heiz and Professor Ian D. Sharp, both at TUM. The third Fellow, Professor Natalia B. Shustova from the University of South Carolina will be hosted by TUM-Professors Roland Fischer and Tom Nilges. All three guests will be working on the creation of new materials for energy conversion and on understanding the associated energy conversion processes.

Cheap and lead-free materials for solar cells

The research project of Laura Herz is entitled “Controlling Charge-Carrier and Ion Dynamics in Lead-free Halide Perovskites for Photovoltaics.” Perovskite solar cells have created enormous excitement in the context of energy conversion. Their light-harvesting layer commonly consists of a lead halide-based perovskite material, shortly Halide Perovskite (HaP). Those materials can be produced cheap and simple and, at the same time, offer very promising optoelectronic properties for photovoltaic applications. In only a few years, their power conversion efficiency has rapidly increased from an initial value of 3.8% to over 25% in recent reports, while using much less energy for device production than for traditional silicon devices.

Empirical optimization of HaP devices, however, as well as the invention of new materials designs, is now reaching a limit. In addition, most of those materials so far are toxic since being lead-based. With strongly intertwined experimental, theoretical, and synthetic research efforts, Laura Herz, Thomas Bein and David Egger are aiming to enable the design of novel lead-free HaP compounds with superior functionality regarding optoelectronic and stability properties, and offering high power-conversion efficiencies when implemented in solar cells.

The scientists have identified control of charge-carrier and ion dynamics as key challenges that need to be addressed. These features are associated with some of the most important fundamental processes in HaPs for energy technologies. They are key to commercializing potentially disruptive technologies of converting sunlight into electricity with high efficiency, since carrier dynamics control crucial optoelectronic properties like mobilities and ion dynamics dictate material stability, being one of the major bottlenecks of HaP photovoltaics technology.

Inspired by Nature: optimizing photocatalysis

Ib Chorkendorff’s research at TUM under the title “Orchestrating Light-Induced Molecular Transformation by Tuning Co-Catalyst Size and Dimension” focuses on the conversion of solar energy into solar fuels. Storing solar energy in the chemical bonds of a fuel can thereby proceed in various ways. Renewably generated electricity could be used to drive electrochemical cells that convert abundant chemical species such as H₂O or CO₂ into useful fuels.

Alternatively, and inspired by the concept of photosynthesis, photoelectrochemical or photocatalytic systems would directly harness the solar energy to produce hydrogen or hydrocarbon fuels, without the need to separately generate electricity. Release of the stored energy could finally proceed via reaction with an oxidizer, typically air, either electrochemically in fuel cells (FCs) or by combustion, as is usually the case with fossil fuels, yet at neutral carbon footprint.

The special focus of Chorkendorff’s project lies in designing stable and efficient catalysts for the photocatalytic Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER), as well as on the efficient hydrogenation of CO₂ for the synthesis of solar fuels. In this context, the researchers aim to obtain a fundamental understanding of the chemical processes involved and particularly to investigate the influence of size and dimension of the catalytic particles on the conversion of solar energy into solar fuels.

New hybrid materials for the study of energy and electron transfer

The project of Natalia Shustova will focus on new hybrid materials for the study of energy and electron transfer (ET) processes. This is a cornerstone of modern physical and inorganic chemistry, which is driven by growing demand in efficient energy transfer and conversion necessary to build a sustainable energy society independent from fossil fuels. Specifically, materials with a predesigned pathway for ET can address the urgent needs in the fast enhancement of material performance in areas ranging from optoelectronic devices to photocatalytic systems and, thereby, drastically modify the existing energy and material landscape.

Well-defined hierarchical hybrid materials, such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) being the focus of the synergetic collaboration of Shustova and Fischer groups have significant advantages to achieve directional ET. For instance, they provide a high level of control for chromophore arrangement, structural parameters (including distance, angles, and molecular conformation), and photophysical properties, through rational chromophore design and synthetic conditions unprecedented for large light-harvesting ensembles and extended structures.

However, to harness these hybrid scaffolds as a versatile platform for energy utilization enhancement, mechanistic and structural aspects governing ET efficiency should be elucidated first. Therefore, preparation of materials with a predesigned pathway for ET still remains a noteworthy challenge. Addressing this challenge is a goal of the collaboration between the Shustova and Fischer groups. Thus, the major goal is to demonstrate that materials with a predesigned pathway for energy transfer can be rationally prepared to elucidate the mechanistic and structural aspects, which are required to achieve efficient and directional ET.

Strengthening the Cluster of Excellence

With the world-leading expertise of the guests, the fellowships will greatly strengthen the activities of the Cluster of Exellence e-conversion. Being members of the Scientific Advisory Board of e-conversion, two fellows (Laura Herz and Ib Chorkendorff) will benefit by obtaining direct insights into the organization and functioning of the cluster, which will provide a strong basis for giving strategic advice to the cluster.

An important part of all three projects will be the organization of international, interdisciplinary conferences in Munich. These will bring together world-leading researchers of the respective fields. It is intended to not only present recent research results but also to outline future trends in the development of new materials and conversion processes in energy science.

The Fellows:

Prof. Laura Herz (University of Oxford, UK, Department of Physics, Semidonductor Group) is one of the internationally leading figures in the research on halide perovskites for photovoltaics. Her discoveries have given crucial insight to that field with regards to fundamental charge-carrier mobility and recombination mechanisms, material composition and morphology, electrical doping, light emission, and structural considerations.

Prof. Ib Chorkendorff (Technical University of Denmark, Department of Physics, Surface Physics & Catalysis) brings world-leading expertise in sustainable energy conversion and fundamental heterogeneous catalysis. He offers unique technical know-how on the generation of new nanomaterials as well as on microreactors and the detection of reaction products with highest sensitivity.

Prof. Natalia Shustova (University of South Carolina) is a rising star in the highly competitive field of metal-organic and covalent-organic frameworks. She has already established novel strategies for light harvesting and energy transfer based on such host structures. Her research direction offers a substantial overlap with activities in the Cluster of Excellence e-conversion.

The TUM-IAS Fellowhips:

The Technical University of Munich has established its Institute for Advanced Study (TUM-IAS) with the goal of creating fields of excellence in “Science and Technology”. Embedded in a comprehensive technical university, TUM-IAS seeks to promote research in fields ranging from natural and applied sciences, life sciences and medicine to all areas of engineering, many of which are strongly influenced by modern science. TUM-IAS awards Fellowships to distinguished researchers and gives them the necessary time and financial support to explore new venues, to develop novel research areas, especially at the border between classical disciplines, and to establish intensive international collaborations as well as collaborations with industry.

The Hans Fischer Senior Fellowships are available for outstanding international scientists who intend to explore innovative, high-risk topics in their scientific research areas together with a TUM Research Group. The fellowships are named after TUM professor Hans Fischer (1881–1945), who was awarded the Nobel Prize in Chemistry in 1930 for his pioneering work on hemoglobin and related structures. The Fellowships last 3 years with the expectation that the Fellow will spend a total of at least 9 months at TUM (which can be divided individually into several stays). Hans Fischer Senior Fellows receive an award of €60,000 plus €50,000 for travel, housing and research related costs. A further €50,000 can be allocated to the Fellowship if required. Hans Fischer Senior Fellows also receive support for one doctoral candidate at TUM, who will be co-advised by the TUM Host professor and the Hans Fischer Senior Fellow.

The Cluster of Excellence e-conversion:

e-conversion is a Cluster of Excellence funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany‘s Excellence Strategy since January 2019. The cluster unites about 40 scientists and their research groups from the Munich area as well as from Max Planck Institutes in Stuttgart and Mülheim an der Ruhr. Together, the researchers investigate the fundamental processes involved in the conversion of renewable energies.