Prof. Christina Birkel
Title: Synthesis science and functional properties of layered solids and 2D materials
Bio:
Christina Birkel is an Associate Professor in the School of Molecular Sciences at Arizona State University (ASU) and holds a joint professorship position in the Department of Chemistry and Biochemistry at the Technische Universität (TU) Darmstadt. In 2024, she was appointed Navrotsky Professor of Materials Research at ASU. Prior to her independent career, she was a Junior Research group leader at TU Darmstadt (Habilitation in 2018), a Postdoctoral Researcher (group of Prof. Galen Stucky) at the University of California, Santa Barbara (Feodor Lynen Research Stipend, Alexander-von-Humboldt Foundation) and completed her PhD thesis (group of Prof. Wolfgang Tremel) at the Johannes Gutenberg-University of Mainz holding a stipend of the Graduate School of Excellence (2010). Her group focuses on the synthesis and structural science of new types of layered solids and two-dimensional materials with a strong focus on carbides and (carbo)nitrides (MAX phases and MXenes), as well as the investigation of their properties including transport (electronic, magnetic), high-temperature and electrochemical behavior.
Abstract:
Synthesis science is often treated as an afterthought during our search for and optimization of (functional) materials. Our team tackles this by using a holistic approach to preparation techniques and linking synthesis variables to materials characteristics and ultimately their properties. In that general framework, we focus on layered solids and two-dimensional materials where we strive to prepare new versions of them – in terms of chemical composition and morphology, for example – as well as in situ method development to gain insight into formation pathways under different synthesis conditions. We are particularly interested in carbides and (carbo)nitrides that belong to the large, and growing, families of MAX phases and MXenes. MAX phases consist of early-to-mid transition metals (M), (typically) main group elements (A) and carbon and/or nitrogen (X) and crystallize in a hexagonal structure with alternating layers of M6X octahedra and layers of the A element. The order of the layers is flexible leading to different stoichiometries, mainly M2AC, M3AC2 and M4AC3. The A element, especially in the case of Al (and Ga), can be removed by chemical etching leading to the two-dimensional siblings, MXenes, that are obtained as van der Waals-stacked multilayers and eventually delaminated (single) nanoflakes.
In this talk, I will highlight a few examples of our recent research on the preparation of carbonitride MAX phases, the functional properties of Cr-containing MAX phases and electrocatalytic properties of Mo-containing MXenes. Aside from conventional solid-state synthesis techniques, we use non-conventional heating methods, especially microwave heating, and we have developed a sol gel-based approach to access many of the compounds. To understand the properties of the materials, we investigate their structure and microstructure in great detail using diffraction, spectroscopy and imaging techniques. This guarantees informed discussions of their (functional) properties and enables us to propose guidelines for the development of new types of materials (ceramics).
Keywords: Solid state chemistry, Materials chemistry, Layered solids, 2D materials, Carbides