Speaker
Description
Solid oxide cells, including solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) are becoming increasingly important due to their relatively high energy conversion efficiencies of up to 85 %. This makes solid oxide cells a valuable element to complement the modern energy infrastructure by providing chemical storage capacities for excess energy that temporarily arises due to the intermittent nature of renewable energy sources such as wind or solar power. Rapid deactivation presently limits a widespread use of high-temperature solid oxide cells (SOCs) as otherwise highly efficient chemical energy converters. With deactivation triggered by the ongoing conversion reactions, an atomic-scale understanding of the active triple-phase boundary between electrolyte, electrode, and gas phase is essential to increase the cell performance.
Here, a multi-modal approach is used that combines synergistically the expertises of the AC Department, the Theory Department (Dr. Christoph Scheurer), and IEK-9 of Forschungszentrum Jülich (Prof. Dr. Rüdiger Eichel). It comprises transmission electron microscopy, X-ray spectroscopy, first-principles calculations, and molecular dynamics simulations to untangle the atomic arrangement of the prototypical SOC interface between a lanthanum strontium manganite (LSM) anode and an yttria-stabilized zirconia (YSZ) electrolyte in the as-prepared state after sintering. An interlayer of self-limited width with partial amorphization and strong compositional gradient is identified, thus exhibiting the characteristics of a complexion that is stabilized by the confinement between two bulk phases.[1] Furthermore, theoretical modelling predicts a three-times higher diffusion rate within the complexion compared to the vicinal bulk phases as well as an enrichment of Sr and Mn cations at the surface of the complexion. In order to experimentally capture these small amounts of Sr at the complexion surface, we combined energy dispersive X-ray spectroscopy mapping with post-acquisition drift correction, multivariate statistical analysis and Welch t-tests. The Sr surface enrichment after thermal annealing was further corroborated by X-ray photoelectron spectroscopy. This combination of techniques allowed us to experimentally validate the theoretical results and shows the possibility to detect the origins of phase segregation which is an important addendum in order to conclude on the dominant deactivation mechanism.[2]
In summary, we propose a complexion-mediated cation segregation pathway, which forms at the electrode/electrolyte interface. Instead of migrating via the LSM bulk to the surface, where cation diffusion is severely limited, cations close to the grain boundary diffuse into the complexion, which features a significantly enhanced ion mobility. The enhanced diffusion in the complexion leads to a faster thermodynamic equilibration, which according to experiment and simulation leads to Sr and Mn oxide formation at the complexion surface. This offers a new perspective to understand the function of SOCs at the atomic scale and opens up a hitherto unrealized design space to tune the conversion efficiency.
More details on the theoretical aspects are presented on poster TH.16 of the theory department.
References
[1] H. Türk, F.-P. Schmidt, T. Götsch, F. Girgsdies, A. Hammud, D. Ivanov, I. Vinke, L.G.J. de Haart, R.A. Eichel, K. Reuter, R. Schlögl, A. Knop-Gericke, C. Scheurer, T. Lunkenbein Advanced Materials Interfaces 2021, 8, 2100967.
[2] H. Türk, T. Götsch, F.-P. Schmidt, A. Hammud, D. Ivanov, I. Vinke, L.G.J. de Haart, R.-A. Eichel, K. Reuter, R. Schlögl, A. Knop-Gericke, T. Lunkenbein, C. Scheurer ChemCatChem, 2022, DOI: 10.1002/cctc.202200300.
| Abstract Number (department-wise) | AC 6.3 |
|---|---|
| Department | AC (Schlögl) |
