Abstract
Experimental studies have shown the possible production of hydrogen through photocatalytic water splitting using metal oxide (MOy) nanoparticles attached to an anatase TiO2 surface. In this work, we performed density functional theory (DFT) calculations to provide a detailed description of the stability and geometry of MxOy clusters M = Cu, Ni, Co, Fe and Mn, x = 1–5, and y = 0–5 on the anatase TiO2(101) surface. It is found that unsaturated 2-fold-coordinated O-sites may serve as nucleation centers for the growth of metal clusters. The formation energy of Ni-containing clusters on the anatase surface is larger than for other M clusters. In addition, the Nin adsorption energy increases with cluster size n, which makes the formation of bigger Ni clusters plausible as confirmed by transition electron microscopy images. Another particularity for Ni-containing clusters is that the adsorption energy per atom gets larger when the O-content is reduced, while for other M atoms it remains almost constant or, as for Mn, even decreases. This trend is in line with experimental results. Also provided is a discussion of the oxidation states of M5Oy clusters based on their magnetic moments and Bader charges and their possible reduction with oxygen depletion.
Highlights
The over-exploitation of the fossil energies leads to a significant increase of CO2 in the atmosphere, resulting in severe climate problems
Spin-polarized density functional theory (DFT) calculations were carried out to investigate possible stable structures of five different transition metal clusters, namely Cu, Ni, Co, Fe and Mn adsorbed on the anatase TiO2 (101) surface
Ni has the largest adsorption energy, and for all metals except Ni the adsorption energies decrease with increased number of adsorbed atoms, so that probably only Ni prefers to form bigger clusters on the TiO2 surface in agreement with experimental transition electron microscopy (TEM) results [9]
Summary
The over-exploitation of the fossil energies leads to a significant increase of CO2 in the atmosphere, resulting in severe climate problems. It is absolutely necessary to replace them by alternative energy sources. When using sun light as energy source, materials with specialized properties are necessary, and TiO2 is such a versatile material that has numerous applications in catalysis, photocatalysis, and solar energy [1]. TiO2 crystallizes in three major different structures: rutile (tetragonal), anatase (tetragonal) and brookite (rhombohedral). Other structures exist as well, as for example cotunnite, that has been synthesized at high pressures and is one of the hardest polycrystalline materials known. Only rutile and anatase play an important role in the applications of
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