Oxidation of Ultrathin FeO(111) Grown on Pt(111): Spectroscopic Evidence for Hydroxylation

Using high resolution and ambient pressure X-ray photoelectron spectroscopy we show that the catalytically active FeO $$-{2}$$ 2 trilayer films grown on Pt(111) are very active for water dissociation, in contrast to inert FeO(111) bilayer films. The FeO $$-{2}$$ 2 trilayer is so active for water dissociation that it becomes hydroxylated upon formation, regardless of the applied preparation method. FeO $$-{2}$$ 2 trilayers were grown by oxidation of FeO(111) bilayer films either with molecular oxygen in the mbar regime, or by NO $$-2$$ 2 and atomic oxygen exposures, respectively, in the ultrahigh vacuum regime. Because it was impossible to prepare clean FeO $$-{2}$$ 2 without any hydroxyls we propose that catalytically highly active FeO $$-{2}$$ 2 trilayer films are generally hydroxylated. In addition, we provide spectroscopic fingerprints both for Pt(111)-supported FeO(111) and FeO $$-2$$ 2 films that can serve as reference for future in situ studies.