Berlin 2024 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 10: Topical Session: Hydrogen in Materials: from Storage to Embrittlement I

MM 10.5: Talk

Monday, March 18, 2024, 17:00–17:15, C 130

Hydrogen-driven surface segregation in Pd-alloys from atomic scale simulations — •Pernilla Ekborg-Tanner and Paul Erhart — Department of Physics, Chalmers University of Technology, Gothenburg, Sweden

Pd-based nanoalloys show great promise as plasmonic hydrogen sensors. Nanoalloys are, however, subject to issues related to the chemical order such as surface segregation. The surface composition is directly related to the kinetic properties necessary for H sensing and as such, understanding the surface segregation during fabrication, operation and storage is crucial to ensure long-term stable sensors. In this work, we employ cluster expansions of PdAu and PdCu surface alloys with variable H coverage, trained using DFT calculations and sampled in Monte-Carlo simulations. This approach allows us to study the H coverage and the layer-by-layer composition of the near-surface region as a function of bulk composition, temperature and H pressure. We find that in the case of AuPd, Au segregates to the surface in vacuum while Pd segregates to the surface at full H coverage, and the transition between these regimes occurs over a narrow H pressure interval. In the case of CuPd, on the other hand, the H coverage varies much more gradually with H pressure and and is coupled to a non-monotonic variation of the Cu concentration in the topmost surface layer. The results demonstrate the rich behavior that can result from the coupling of metal-metal and metal-hydrogen interactions at surfaces, even in apparently simple but concentrated systems.

Keywords: Surface segregation; Palladium; Hydrogen; Alloy; Cluster expansion