Potential-Induced Segregation Phenomena in Bimetallic PtAu Nanoparticles: An In Situ Near-Ambient-Pressure Photoelectron Spectroscopy Study.

The surface properties of a model membrane electrode assembly of a high-temperature proton-exchange-membrane fuel cell with a nanostructured PtAu working electrode were studied under operando conditions (polarization, humidified H₂ atmosphere, 150 °C) using near-ambient-pressure photoelectron spectroscopy (NAP-XPS). NAP-XPS proved to be a powerful tool for the in situ investigation of the changes in the chemical composition, the segregation of the two metals, and the changes in their oxidation state. Nondestructive depth profiling revealed the influence of the polarization and the gas ambient on the distribution of the two metals in the near-surface region. The results suggest that the surface of the electrode is covered by a thin layer of gold, which is stable at potentials below the onset of surface-oxide formation. Anodic oxidation of the PtAu electrode pulls Pt to the surface, leading to intermixing of Pt and Au atoms and the formation of an interfacial alloy. [ABSTRACT FROM AUTHOR]