Reactions of NO and H2O on the PuO2 {111} surface: A DFT study

The effect of the Hubbard U parameter is explored in periodic boundary condition PBE+U calculations of a variety of properties of bulk PuO2 and its {111} surface. Comparison is made with experimentally-determined bulk and surface properties, including band gap and lattice parameter, hybridization of the Pu 5 f and O 2 p states at the top of the valence band, peak separation in the valence band, and the {111} surface work function. Comparative PBE0 calculations, and the Bader charges of the atoms in the {111} surface, are also assessed. A U value of 3 eV is recommended, and is used in PBE+U study of H2O and NO reacting both individually and sequentially on PuO2 {111}. For NO interacting individually, approach to the surface is orientation-dependent, and surface-bound NO forms defect surface states between the valence and conduction bands. For water reactions with and without NO present on the surface, the Pu 5 f band centre plays a major role in the reactions. When NO is present, a linear relation emerges between water adsorption energy and 5 f band centre relative to the Fermi level. Both Pu 5 f band centre relative to the Fermi level and the energetic gap between the 5 f band centre and 2 p band centre of the water O govern the barrier to water splitting. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Automated summary

The effect of the Hubbard U parameter on the properties of bulk PuO2 and its {111} surface was investigated using periodic boundary condition PBE+U calculations. Comparison with experimental data was conducted for various properties, including band gap, lattice parameter, hybridization of Pu 5 f and O 2 p states, peak separation in the valence band, and surface work function. A U value of 3 eV was recommended and used to study the reactions of H2O and NO on PuO2 {111}, both individually and sequentially. The role of Pu 5 f band centre and its relation to the Fermi level were found to be significant in determining the reactions.