High-Coverage H2 Adsorption on the Reconstructed Cu2O(111) Surface

The adsorption of H2 on the Cu2O(111) surface has been studied by spin-polarized density functional theory (DFT+U) calculations and atomic thermodynamics. It has been found that there exists reconstruction on a stoichiometric Cu2O(111) surface. The probability distribution of the reconstructed Cu2O(111) surfaces as a function of temperature has been analyzed using Boltzmann statistics. It has been found that the molecular H2 prefers to adsorption on the uncoordinated CuCUS atom at low coverages (1/4 or 1/2 monolayer), while totally dissociative H2 is preferred on the reconstructed Cu2O(111) surface at higher coverages (3/4 or 1 monolayer). For H2 splitting on the Cu2O(111) surface, homolytical dissociative adsorption on two surface-uncoordinated CuCUS atoms is preferred which is a new mechanism for H2 on metal oxides. More interesting is that the surface reconstruction will be recovered for eight hydrogen atoms binding on four uncoordinated CuCUS and four uncoordinated OCUS atoms at saturation coverage. It has been found that the adsorbed H atoms will put out the lattice oxygen to the surface at higher coverage (five and six H2), which agrees well with the experimental findings. The phase diagrams of H2 binding on ideal and reconstructed Cu2O(111) surfaces were plotted and analyzed. In addition, we compared and analyzed the adsorption mechanisms of H2 splitting on different metal oxides.