Coordination: Yujiao Li

B01 aims to assess the phase stability of new CCSS, select thermally stable single-phase CCSS among many candidates in an accelerated manner, and provide additional data on surface segregation, surface composition, as well as GB segregation of the selected homogeneous (nanocrystalline) CCSS at different temperatures. These data will contribute to other CRC projects for further in-depth studies on smooth (coarse-grained) CCSS in order to understand and control their SAA. To achieve these goals, B01 will use the CPP approach, comprising APT, TEM and correlative APT/TEM, to perform near-atomic-scale analyses of 3D chemistry and crystal structure.

Coordination: Tong Li

B02 will reveal the elemental distribution on the surface planes and grain boundaries of selected CCSS systems at the atomic scale in the as-deposited state and after annealing and provide a thorough analysis regarding types and numbers of atomistic configurations of nanoclusters or nanoscale chemical modulations on the surface plane and at grain boundaries and corresponding adsorbates before and after HER. Additionally, B02 will correlate the atomic-scale compositional analysis with its corresponding electrochemical properties, thereby identifying an optimal combination of surface coordination that yields the best electrochemical properties. Overall, B02 will establish the interplay between heat treatments, surface atomistic configuration, and electrochemical performance of CCSSs towards HER, providing atomistic insight into the design of effective HER electrocatalysts.

Coordination Christina Scheu, Christoph Somsen

Project B03 will investigate how changes in surface chemistry and structural order (e.g., segregation and ordering versus random solid solution) as well as other defects will affect CCSS properties. The atomic configuration at the surface will be determined with highest spatial resolution using aberration-corrected (S)TEM imaging and analytical techniques. Attention will also be paid to changes caused by annealing and electrochemistry. Possible surface segregation, ordering phenomena and atomic distances within the (sub)surface will be evaluated in cross-section.

Coordination: Baptiste Gault, Christoph Freysoldt

No microscopy and microanalysis technique readily exists that can analyse these three-dimensional atomic motifs with true atomic resolution in real space and high chemical sensitivity, which are necessary for analysing the SAA in CCSS. Field-ion microscopy was the first technique allowing direct imaging of individual atoms at the surface of a metal. However, its inability to discern the elemental nature of the imaged atoms made it obsolete, and it was superseded by atom probe tomography. PI Gault and PI Freysoldt pioneered an approach that combines cutting-edge experimental and theoretical work, based on density-functional theory, to provide FIM with an ability to determine which element is being imaged, and project B04 will advance this new technique termed analytical FIM in order to analyse catalytically active SAA in CCSS. 

Coordination: Karina Morgenstern

B05 plans to use scanning tunnelling microscopy for an atomic-scale view of the surfaces of CCSS in real space, their elemental composition and distribution of the elements across the surface. Because of the low chemical sensitivity of scanning tunnelling microscopy, the challenge to discriminate five different elements on a surface demands the development of novel tools to determine the SSA of CCSS in real-space. 
Three main approaches, i.e., dz/dV mapping, chemically sensitive imaging, and local phonon spectroscopy, will be supplemented by discrimination via spectator molecules, CO or water. The results will aid the fabrication of targeted CCSS and their modelling in its partner projects.