Interfaces in energy materials
Interfaces in energy materials hold utmost significance due to their profound impact on performance and reliability. In the realm of energy storage and conversion devices, such as batteries, fuel cells, and solar cells, interfaces play a critical role in governing key processes like charge transfer, ion diffusion, and electrochemical reactions. The mechanical behaviour at these interfaces is closely linked to the structural stability and durability of the materials, which are crucial for long-term operation under varying conditions. Understanding the mechanics of interfaces enables the identification and mitigation of failure mechanisms, such as cracking, delamination, or stress-induced degradation, ultimately leading to the development of materials with enhanced mechanical integrity. Moreover, comprehending the interplay between mechanics and chemistry at interfaces empowers researchers to optimise material design, tailor interfacial properties, and unlock the full potential of energy materials, driving advancements towards sustainable and efficient energy solutions.
Defects in electrode materials: The electrochemical performance of energy materials are strongly influenced by defects such as interfaces, dislocations, and grain boundaries. These defects can alter the diffusion pathways for ions and electrons, affecting the overall charge storage and transfer kinetics, which directly impact efficiency, cycling stability, and lifespan. For water electrolysis, iron oxides have garnered significant attention as model electrode materials for the oxygen evolution reaction (OER). In recent years, the relationship between the microstructure of electrode materials and their electrochemical performance during OER have been studied. In particular, defect engineering offers the ability to fine-tune the OER activity of electrodes where surface defects, such as oxygen vacancies or edge dislocations, can serve as active sites for the OER reaction. Nina Nicolin, supported by the IMPRS SusMet program and in collaboration with Prof. Kristina Tschulik, looks at defects in reactive magnetron sputtered iron oxide thin-films as model spinel materials to investigate the influence of the microstructure on the catalytic performance during OER. The connection between structural and compositional details and electrochemical performance will be studied using local analysis techniques such as scanning electrochemical cell microscopy (SECCM) to obtain novel insights into the role of defects on electrochemical performance. Complementary to this direction, visiting PhD student Nant Nammahachak from KMUTT is following the effect of oxygen vacancy transport to grain boundaries in strontium titanate, and quantifying the effects on electrical and nanomechanical response under UV light irradiation, linked to fuel cell electrode technology.
Nanostructured thin-films for electronics: Thin-films are crucial for electronics applications due to their ability to provide compact, lightweight, and flexible components, enabling the development of portable devices and wearable electronics. Additionally, thin-film technologies allow for precise control over material properties, making them essential for fabricating high-performance electronic devices with enhanced functionality and efficiency. Led by former group member Dr. Hanna Bishara, we recently reported on Fe-doped Cu thin-films produced by magnetron sputtering, where the Fe localisation to grain boundaries could be controlled by thermomechanical processing with effects on the electrical conductivity (Scripta Materialia, 230, 2023, 115393). Recent work from the group has looked at nanostructuring and resulting effect on mechanical properties in amorphous Ni-P thin-films which have applications as metallisation layers in power electronics devices. Andrea Brognara and visiting PhD student Cristiano Poltronieri have also focussed on amorphous thin-films, but magnetron sputtered thin-film metallic glasses (TFMGs). For this project, in collaboration with Matteo Ghidelli from Sorbonne Paris Nord and supported by the DAAD and CRNS Salto program, we sought to understand how the local chemistry of TFMGs affects mechanical and electrical performance. The activation of mechanical size effects TFMGs have been found to be an effective way to improve plastic deformation and strain-to-failure of these amorphous alloys, while the introduction of interfaces within the glass structure has been shown to further improve the mechanical properties by hindering the propagation of shear bands (SBs). Indeed, for our systems micropillar compression shows that the bilayer period (Λ) mediates the deformation mode, from the formation of single SBs and consequent catastrophic brittle failure to SB multiplication. Furthermore, fully amorphous multilayered ZrCu/ZrCuAl TFMGs were deposited by magnetron co-sputtering with different bi-layer periods and tested mechanically. Despite the similar elastic properties of the two monolithic materials, the crucial effect of Λ was also observed on failure. Overall, nanostructuring shows to be an effective strategy for tuning the behaviour of both crystalline and amorphous metallic thin-films.
Failure in solid-state lithium ion battery systems: An emerging research topic of this group, where we strengthen a collaboration with the group of Prof. Jennifer Rupp at TU Munich. Currently Till Freieck is looking at the environmental stability of battery component materials, to allow for rational experimental planning.