Electron Microscope group
Our research focuses on exploring the effect of local structures on the surface properties, the localized formation of working structures and function of a catalyst. To this end, we take an interdisciplinary and understanding-based research approach that combines detailed and complementary structural analysis by electron microscopy and X-ray diffraction (XRD), inorganic synthesis chemistry, and catalytic testing. For this purpose, we also develop analytical methods and measurement setups for chemical and operando electron microscopy.
In the field of chemical electron microscopy, we complement imaging with electron energy loss spectroscopy (EELS), electron diffraction (ED), and electron dispersive X-ray spectroscopy (EDX). Self-developed setups for operando scanning electron microscopy (OSEM) and operando transmission electron microscopy (OTEM), as well as quasi in situ TEM, allow us to obtain a multi-scale structural and morphological information of the changes in a catalyst during reaction while determining its function.
(Operando) XRD measurements are performed in Bragg-Brentano or transmission mode to analyze the average crystal structure of powders. In addition, grazing incidence XRD (GIXRD) and X-ray reflectometry (XRR) measurements allow the structural characterization of films.
The reaction base includes studies on the structure and degradation of functional materials for the electrochemical production of "green" hydrogen, heterogeneous catalysts for chemical energy conversion and industry. In this respect, the materials base includes metallic and oxide thin films and powder catalysts for ammonia synthesis and decomposition, CO2 activation and conversion, high temperature water splitting, selective oxidation of hydrocarbons, their hydrogenation and dehydrogenation. Furthermore, we investigate the structures of microplastics and batteries.
Moreover, we pursue a correlative operando spectromicroscopy approach in close collaboration with the Electron Structure Group of the Department of Inorganic Chemistry, the Department of X-ray Microscopy and the Institute of Nanospectroscopy of Helmholtz-Zentrum Berlin. Covering a broad range of magnifications ranging from optical microscopy over scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) down to sub angstrom resolution imaging using state of the art Cs corrected transmission electron microscopy (TEM), we study the structural characteristics of catalysts. Structural information is complemented with information about the elemental composition which is acquired using appropriate techniques for different size dimensions of the analyzed volume. The techniques range from X-ray fluorescence spectroscopy for average composition to energy dispersive X-ray (EDX) spectroscopy and EDX mapping in the electron microscope for more localized information. Furthermore, electron energy loss spectrometry (EELS) is used to provide further details about the elemental composition and electronic structure. Interpretation of the experimental data is supported by image simulations on the structure side and band structure calculation of the electronic structure and the simulation of EELS spectra on the other.