1. Origin of Surface Reduction upon Water Adsorption on Oriented NiO Thin Films and Its Relation to Electrochemical Activity
- Author
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Raphaël Poulain, Jochen Rohrer, Yannick Hermans, Christian Dietz, Joachim Brötz, Joris Proost, Marian Chatenet, Andreas Klein, UCL - SST/IMMC/IMAP - Materials and process engineering, Technische Universität Darmstadt - Institute of Materials Science, Electronic Structure of Materials, Technische Universität Darmstadt - Institute of Materials Science, Materials Modelling, Technische Universität Darmstadt - Institute of Materials Science, Physics of Surfaces, and Technische Universität Darmstadt - Institute of Materials Science, Structural Research
- Subjects
Surfaces ,Coatings and Films ,General Energy ,Electronic ,Optical and Magnetic Materials ,Physical and Theoretical Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
The interaction of water with oriented NiO films is studied by using a combination of photoelectron spectroscopy with in situ sample preparation and electrochemical measurements in the stability window of water. In contrast to NiO(100), room temperature water exposure induces a downward band bending on the (110)- and (111)-oriented films, indicating a more positive surface charge. The surface charge is assigned to a dissociative adsorption of water accompanied by a removal of oxygen, which corresponds to a preferential adsorption of protons. Photoelectron spectroscopy suggests that the nonstoichiometric adsorption is related to the presence of adsorbed oxygen species prior to water exposure. For the NiO(110) surface, the stability of adsorbed bridging oxygen dimers is confirmed by density functional theory calculations. The preferential adsorption of protons, which requires interaction of two water molecules with the oxygen dimers, explains that water acts as an electron donor on many oxide surfaces. The different adsorption behavior is consistent with a lower electrochemical activity of the (110)- and (111)-oriented surfaces toward hydrogen adsorption due to an effective reduction of Lewis base sites.
- Published
- 2022