Effect of surface segregation on the oxidation resistance of Cu3Pt(100)

Abstract

Alloying element segregation often occurs under a reactive environment but its interplay with the subsequent surface oxidation of the alloy remains unclear. Using synchrotron-based ambient-pressure x-ray photoelectron spectroscopy, we dynamically monitor the surface segregation in ${\mathrm{Cu}}_{3}\mathrm{Pt}(100)$ in response to temperature and oxygen gas. Vacuum annealing leads to surface segregation of Cu along with the enrichment of Pt in the subsurface region. Upon switching to the ${\mathrm{O}}_{2}$ atmosphere, dissociative chemisorption of oxygen does not change the surface segregation profile from that under the vacuum annealing condition. A stepwise increase in the oxygen pressure results in the transformation pathway of $\mathrm{Cu}\ensuremath{\rightarrow}{\mathrm{Cu}}_{2}\mathrm{O}\ensuremath{\rightarrow}\mathrm{CuO}$, in which the selective oxidation of Cu gives rise to further accumulation of Pt underneath the oxide/alloy interface that hinders the supply of Cu from the bulk to the oxide/alloy interface, thereby leading to the termination of the surface oxidation after the ${\mathrm{Cu}}_{2}\mathrm{O}\ensuremath{\rightarrow}\mathrm{CuO}$ conversion is completed. This differs from the transformation pathway of $\mathrm{Cu}\ensuremath{\rightarrow}{\mathrm{Cu}}_{2}\mathrm{O}\ensuremath{\rightarrow}{\mathrm{Cu}}_{2}\mathrm{O}$/CuO for the oxidation of pure Cu and Cu-Au alloys, in which the oxidation of Cu continues and the ${\mathrm{Cu}}_{2}\mathrm{O}$/CuO bilayer growth is constantly maintained. These key differences provide useful insight into alloy design for controlling the surface properties such as corrosion resistance and catalytic performance of Cu base alloys.