The nature of the interactions between Pt and TiN, a material of interest as a support for proton-exchange-membrane (PEM) fuel cell applications, have been examined in ultrahigh vacuum (UHV) using X-ray photoelectron spectroscopy (XPS). For small amounts of Pt, a reaction takes place yielding XPS features consistent with formation of the intermetallic compound PtTi. Increasing the amount of Pt shifts the 4f(7/2) electron binding energy toward that of metallic Pt. Complementary angle-resolved XPS revealed that Pt remains in the outer surface region of the resulting multicomponent film. The results show that TiN layers with a thickness of only ca. 1 nm already form an effective barrier to Pt diffusion at room temperature. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.012206esl] All rights reserved.