Surfaces and Defects in Multifunctional Compositionally Complex Solid Solution Surfaces
 

The development of novel electrocatalysts is of critical importance for the advancement of sustainable energy technologies, including fuel cells and electrolysers. The most promising candidates are compositionally complex solid solutions (CCSS), which consist of five or more different elements mixed in a single-phase structure. CCSS have the potential to be designed with unique electrocatalytic properties, largely driven by the vast number of active sites on their surfaces. These diverse surface atomic arrangements (SAA) have the possibility of overcoming the limitations of conventional electrocatalysts. However, the intrinsic complexity of SAA structures and their associated chemistry remains challenging to fully comprehend, presenting a significant obstacle to fully harnessing their potential.

The Collaborative Research Center (CRC) 1625, entitled "Atomic-scale Understanding and Design of Multifunctional Compositionally Complex Solid Solution Surfaces," aims to utilize CCSS as a platform for material design. The objective of this initiative is to establish a comprehensive theoretical and experimental understanding of CCSS surface features at the atomic scale. The distinctive properties of CCSS are ascribed to the considerable number of poly-elemental active sites dispersed throughout their surfaces. To elucidate the fundamental principles that govern these materials, CRC 1625 employs a range of high-throughput methodologies, including atomistic simulations, material synthesis, advanced characterization, electrochemical testing, and atomic-scale experiments.

The objective of subproject B03 is to gain insight into the impact of surface chemistry, structural order (including phenomena such as segregation, ordering, and random solid solution), and other defects on CCSS properties. The atomic configurations at CCSS surfaces will be determined with high spatial resolution by employing advanced techniques, including aberration-corrected (S)TEM imaging and analytical methods. Further studies will focus on the effects of annealing and electrochemical treatments, emphasizing phenomena like surface segregation, ordering, and atomic distances within the (sub)surface regions. Cross-sectional analyses will additionally provide insights into these processes. This subproject will collaborate with synthesis, electrochemical performance, other advanced characterization teams to deepen the understanding of CCSS, bridging atomic-scale insights with practical applications.