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

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 oxidation states across the near-surface region. At elevated temperatures, enhanced V segregation leads to lower-valence V oxides at the outermost surface despite increased oxygen uptake. In contrast, the V-depleted subsurface exhibits higher V oxidation states, attributed to increased oxygen coordination around the remaining V species. This surface–subsurface contrast 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 reactive alloy systems such as Pt-based catalysts.