Insights into the Reactivity of the Mn₃O₄(001) Thin Film with Water

Abstract

The correlation between the geometric structure and reactivity of an oxide surface is crucial to designing new catalytic materials. This work uses a wellordered Mn 3 O 4 (001) thin film phase to investigate water-oxide interaction. Based on scanning tunneling microscopy data, we propose that water molecule adsorption occurs at oxygen-defective sites and is followed by water dissociation. The vibrational modes related to the D 2 O (heavy water) physisorbed and the chemisorbed O s D on the surface were identified by infrared reflection absorption spectroscopy at the cryogenic temperature range. Photoelectron spectroscopy at near ambient pressure shows that the water adsorption at defective sites reaches a saturation condition. For water pressures lower than 1 × 10 −4 mbar, the crystalline structure of the Mn 3 O 4 (001) thin film is preserved. Temperature-programmed spectroscopy probed the desorption process and showed that the water interaction induces a phase transition from Mn 3 O 4 to MnO.