Redox dynamics of 2D crystalline vanadium oxide phases on high-index anatase facets

Abstract

Vanadium oxides exist in a multitude of phases with varying structure and stoichiometry. This abundance of phases can be extended through the use of other oxides as supports, and through redox treatments. However, the combined effects of different supports and redox treatments can be difficult to identify, particularly when present as different terminating facets on nanoparticles. Here, we examine structural dynamics of 2D vanadium oxides supported on anatase TiO₂ nanoparticles, correlated with changes in oxidation state, using in situ transmission electron microscopy imaging and electron energy loss spectroscopy. As the average oxidation state is reduced below V(IV), an ordered cubic V(II) phase is observed exclusively at the high-index {10l} facets of the support. This local accommodation of highly reduced states is necessary for explaining the observed range of average oxidation states. In turn, the findings show that oxidation states extending from V(V)–V(IV) to V(II) can be simultaneously stabilized by different supporting oxide surfaces during exposure to atmospheres with controlled redox potential.