Plenary session

2023 Czochralski Award Recipient

How MXenes Expand and Change the Nanomaterials World

MXenes (carbides, nitrides, oxycarbides and carbonitrides of early transition metals) are a very large family of 2D materials. They have a chemical formula of M_n+1X_nT_x, where M is a transition metal (Ti, Mo, Nb, V, Cr, etc.), X is either carbon and/or nitrogen (n=1, 2, 3 or 4), and T_x represents surface terminations (O, OH, halogens, chalcogens). The large variety of structures and compositions, availability of solid solutions on M and X sites, and control of surface terminations offer a plethora of materials to produce and investigate.¹ Combining their plasmonic properties with ease in aqueous processing, high electronic conductivity (over 20,000 S/cm), biocompatibility, and excellent mechanical properties, which exceed other solution-processable 2D materials, MXenes have the characteristics enabling numerous applications.² Inherent to their 2D structure, the charge carriers responsible for MXene’s optical responses and electronic transport are very close to the surface that has exceptional ability to undergo reversible chemical and electrochemical reactions to add or change surface terminations. By design of the MXene composition, the carrier plasma can be rendered sensitive to the resulting changes in band structure and state-filling. As a result, properties of MXenes, such as conductivity, work function, plasmon resonance; visible, IR and microwave absorption/reflection can be controlled by introducing reversible or irreversible changes in their surface chemistry. This allows electrochemical modulation of optical and electronic properties by influencing material interactions with electromagnetic wavesover visible, IR, THz and even GHz wavelength ranges. Many technological advances can be enabled by these chemically responsive, conductive materials. In this talk, I explain how optical, electronic and transport properties of MXenes can be manipulated by tuning their chemical composition. This presentation will also demonstrate electrochemical modulation of the optoelectronic properties and describe potential applications of MXenes in photonic, optoelectronic and electrochemical devices.^1,3,4

References:

1. A. VahidMohammadi, J. Rosen, Y. Gogotsi, The World of Two-Dimensional Carbides and Nitrides (MXenes), Science, 372, eabf1581 (2021)
2. K. Maleski, C. E. Shuck, A. Fafarman, Y. Gogotsi, The broad chromatic range of two-dimensional transition metal carbides, Advanced Optical Materials, 9 (4) 2001563 (2020)
3. M. Han, D. Zhang, C. E. Shuck, B. McBride, T. Zhang, R. (John) Wang, K. Shevchuk, Y. Gogotsi, Electrochemically Modulated Interaction of MXenes with Microwaves, Nature Nanotechnology, (2023) https://doi.org/10.1038/s41565-022-01308-9
4. D. Zhang, R. (John) Wang, X. Wang, Y. Gogotsi, In situ monitoring redox processes in energy storage using UV-Vis spectroscopy, Nature Energy, (2023) https://doi.org/10.1038/s41560-023-01240-9

Point Defect Chemistry: The Powerful Basis of Energy Materials Research

Ionic point defects (vacancies and interstitial ions) are the chemical excitations in solids, and their role is analogous to the role of dissociated centers in water or of electrons and holes in silicon. Point defect chemistry is the area that deals with ionic and electronic charge carriers and their interactions. It is fundamental for understanding transport properties, reactivities and storage capacities in the bulk and at interfaces (nanoionics) [1].

The contribution discusses the relevance of a defect-chemical treatment for electrolytes and electrodes in fuel cells, batteries, supercapacitors and photochemical cells.

 [1] J. Maier, Physical Chemistry of Ionic Materials ( Ions and Electrons in Solids), Wiley, 2nd ed. (2023)

Discovery and Acceleration of Emerging Photovoltaics

Keywords: Solar energy, OPV, Perovskites, Materials Genome

The development of complex functional solar materials for organic or perovskite photovoltaics poses a multi-objective optimization problem in a large multi-dimensional parameter space. Solving it requires reproducible, user-independent laboratory work and intelligent preselection of experiments. However, experimental materials science is a field where manual routines are still predominant, although other domains like pharmacy or chemistry have introduced robotics, automation and machine learning long before. In this talk, I will present a fused knowledge-based / data-driven approach to utilize MAPs (material acceleration platforms) for autonomous materials and device discovery in the field of emerging photovoltaic technologies. The impact of this methodology for autonomous material and device discovery will be discussed in terms of contributing to overcome fundamental scientific challenges.

Biography:

Christoph J. Brabec received his PhD (1995) in Physical Chemistry from Linz University, Austria and joined the group of Alan Heeger at UC Santa Barbara (USA) for a sabbatical. He joined the SIEMENS research labs (project leader) in 2001, Konarka in 2004 (CTO), Erlangen University (FAU - Professor for Material Science) in 2009, ZAE Bayern e.V. (scientific director and board member) in 2010, spokesmen of the Interdisciplinary Center for Nanostructured Films (IZNF) in 2013 and became director at FZ Jülich (IEK-11) in 2018. In 2018 he was further appointed as Honorary Professor at the University of Groningen, Netherlands.
His research interests include all aspects of solution processing organic, hybrid and inorganics semiconductor devices with a strong focus on photovoltaics and renewable energy systems. A major research interest are scalable processing technologies allowing to control microstructure formation in disordered semiconductors. A very recent activity explores the limitation of autonomous operating research line for accelerating innovation and inventions in materials science. His combined scientific and technological interests supported the spin-out of several companies. He published over 1000 articles, thereof over 800 peer reviewed articles, about 100 patents, several books and book chapters and overall received 100.000 citations. His h-index is over 140 and Thompson Reuters HRC lists him for the last years consecutively as a highly cited researcher.