XPS spectroscopic study of potentiostatic and galvanostatic oxidation of Pt electrodes in H₂SO₄ and HClO₄

The surface oxides produced from potentiostatic and galvanostatic oxidation of Pt electrodes in HClO₄ and H₂SO₄ are examined using X-ray photoelectron spectroscopy. The oxide I species produced as the initial oxidation product by successively more anodic potentiostatic oxidation in 0.2 M HClO₄ is found to have a Pt²⁺ oxidation state, a binding energy characteristic of neither PtO, Pt(OH)₂ or PtO₂, and a limiting thickness of 8 Å. Galvanostatic oxidation in HClO₄ and H₂SO₄ is found to produce PtO₂·H₂O as an unlimiting growth oxide or a limiting growth oxide layer depending on the concentration of the acid electrolyte. The incorporation of the acid electrolyte anion in the surface layer is shown to have an effect on which type of oxide layer is produced. X-ray decomposition and chemical modification by Ar⁺ stripping are shown to produce chemical artifacts complicating any interpretation of a Pt oxide surface layer.