Mapping Valence Band and Interface Electronic Structure Changes during the Oxidation of Mo to MoO3 via MoO2 and MoO3 Reduction to MoO2: A NAPPES Study

Abstract

Tuning the surface energetics, especially work function (ϕ) of the materials, is of a great deal of interest for a wide range of surface- and interface-based devices and applications. How the ϕ of a solid surface changes under the reaction conditions is of paramount interest to the chemists, particularly in the areas of surface-dependent phenomena such as, catalysis and electrochemistry. In the present study, by using the valence band and core-level photoelectron spectroscopy, surface electronic changes from Mo to MoO3 via MoO2 was studied under relevant near-ambient pressure (NAP) and high temperature conditions. A very significant change in ϕ from Mo to MoO3 was observed and it is well corroborated with the changes in gas-phase vibrational features of O2 in both near-ambient pressure ultraviolet photoelectron spectra (NAPUPS) as well in NAP X-ray photoelectron spectroscopy. Reversible changes in the electronic structure is observed when MoO3 was reduced in H2 to MoO2. On the basis of the extent of oxida...