Deciphering oxygen-induced surface segregation of Pt3V alloy using ambient pressure XPS

Abstract

We investigate oxygen-induced surface segregation and chemical state variations in a polycrystalline Pt3V alloy using synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS), complemented by in situ scanning tunneling microscopy (STM). Upon exposure to sub-millibar O2, vanadium (V) undergoes pronounced surface segregation and selective oxidation, while platinum (Pt) progressively loses chemical bonding with V, particularly at elevated temperatures. Non-destructive, quantitative depth profiling reveals V enrichment at the surface accompanied by V depletion in the subsurface. The competition between V segregation and oxygen uptake produces distinct depth-dependent variations in V oxide evolution pathways across the near-surface region. At elevated temperatures, enhanced V segregation stabilizes lower-valence V oxides at the outermost surface despite increasing oxygen content. In contrast, new higher-valence V oxides continue to emerge in the V-depleted subsurface due to increased oxygen coordination around the remaining V species, despite the less oxygen content compared with the surface. This surface–subsurface divergence in V oxide evolution pathways shows that segregation-driven compositional redistribution can override simple thermodynamic oxidation trends under reactive conditions. These findings provide insight into the interplay among surface segregation, gas–solid interfacial reactions, and alloy oxidation, and establish a mechanistic framework for understanding chemical state variations in alloy systems such as Pt-based catalysts. © 2026 Elsevier B.V.