We investigate the evolution of the surface of a highly alloyed stainless steel (Sanicro 28) upon immersion in aqueous phosphoric acid solutions. For this purpose, both short-(few hours) and long-term immersion (several days) were carried out. A detailed analysis of XPS spectra allowed a distinction to be made between oxygen originating from the organic adlayer (adventitious contamination), the passive oxide layer, and adsorbed phosphate species. By estimating the fraction of oxygen due to phosphate species (O-ph), it was shown that the O-ph/P molar concentration ratio was ranging from about 2 to 3. This suggests the presence of a polyphosphate layer at the stainless steel surface, as also supported by Raman analysis, which influence the electrochemical behavior of SS in the acidic media. (c) 2017 Elsevier B.V. All rights reserved.