Abstract
The stability of Pt-skin on Pt3Co alloy against Co and Pt dissolution with respect to Pt-skin thickness, surface structure and composition is investigated using density functional theory calculations. It is found that, even under oxygen environment, Co migration to the surface is suppressed by the thicker Pt-skin (2–3 Pt atomic layers), confirming experiments. However, the instability of single Pt layer is attributed to the electronic effect of oxygen. The adsorbed oxygen redistributes charge from Pt–Co region to Pt–O region, weakening the Pt–Co bond and facilitating Co migration to surface via Co–O bond formation. We further note that in this system, the Co migrates easier in (111) surface than in (100), attributed to the difference in the oxygen adsorption sites (fcc vs bridge). A minimal negative electrode potential shift of 0.06–0.09 V for Pt dissolution is noted for thicker Pt-skin systems, indicating stability close to pure Pt. The Pt-skin composition is varied by introducing different Migration Barrier Layers (MBLs) = Ru, Rh, Pd, Os, Ir, in the mid-Pt-skin region and found that when MBL is Os or Pd, a novel low-cost composition and more stable MBL-substituted Pt-skin/Pt3Co ORR catalyst emerges.
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