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

The correlation between the geometric structure and reactivity of an oxide surface is crucial to designing new catalytic materials. This work uses a well-ordered Mn₃O₄(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 D₂O (heavy water) physisorbed and the chemisorbed O_sD 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 Mn₃O₄(001) thin film is preserved. Temperature-programmed spectroscopy probed the desorption process and showed that the water interaction induces a phase transition from Mn₃O₄ to MnO.