Speaker
Description
Solid oxide cells (SOCs) are an efficient technology for power-to-hydrogen conversion from fluctuating renewable electricity sources. While SOCs are well adapted to intermittent operation, anode degradation limits cell performance and lifetime in particular in electrolysis mode. This degradation goes hand in hand with the oxygen evolution reaction (OER) located at the triple-phase boundary (TPB) between anode, solid electrolyte, and gas phase. However, the atomistic structure of this active catalyst region is essentially unknown, hindering a detailed analysis of degradation mechanisms and the development of mitigation strategies.
Here, we elucidate the TPB structure and its support, the solid-solid interface between the oxygen-ion conducting electrolyte yttria-stabilized zirconia (YSZ) and the exemplary electrode material strontium-doped lanthanum manganite (LSM). To that end, a tightly linked theoretical and experimental approach had to be developed in a cooperation between the AC and the Theory Department. On the computational side, parallel-tempering Monte Carlo (MC) simulations with a continuously growing cation exchange region centered at the interface yield an efficient approach capable of addressing the structural complexity of this grain boundary region. In the complementary experiments, the spatial resolution of energy dispersive X-ray spectroscopy (EDX) is pushed by a newly developed post-processing routine including drift correction and multi-variate statistical analysis for spectral decomposition. Near-atomic resolution then enables the robust detection of the predicted binary oxide nucleation seeds at the YSZ/LSM interface.
The investigations reveal a complexion at the interface between the two materials forming the compound anode, which features partial amorphization, characteristically varying elemental distribution profiles, and ion mobilities exceeding those of the confining bulk phases. As the complexion's shape and properties are sensitive to its supporting boundary phases and local doping, this finding opens a new path to tune the conversion efficiency of SOCs via interfacial engineering [1,2]. The MC simulation of ensembles of TPB models generated from cutting through the complexion yields insights into the thermodynamic equilibrium state that provides the driving force for cation segregation along the complexion. Based on earlier findings in the literature that correlated the occurrence of binary oxide formation on the surface near the TPB with degradation, we conclude that we have uncovered the hitherto unknown, complexion-mediated deactivation mechanism of the anode [3].
[1] H. Türk et al., Adv. Mater. Interfaces 8, 2100967 (2021).
[2] T. Götsch et al., ECS Trans. 103, 1331 (2021).
[3] H. Türk et al., ChemCatChem, DOI 10.1002/cctc.202200300 (2022).
| Abstract Number (department-wise) | TH 16 |
|---|---|
| Department | TH (Reuter) |
