Reduction mechanisms of the CuO(111) surface through surface oxygen vacancy formation and hydrogen adsorption

Abstract

We studied the reduction of CuO(111) surface using density functional theory (DFT) with the generalized gradient approximation corrected for on-site Coulomb interactions (GGA + U) and screened hybrid DFT (HSE06 functional). The surface reduction process by oxygen vacancy formation and H2 adsorption on the CuO(111) surface is investigated as two different reduction mechanisms. It is found that both GGA + U and HSE06 predict the same trend in the relative stability of oxygen vacancies. We found that loss of the subsurface oxygen is initially thermodynamically favourable. As the oxygen vacancy concentration increases, mixture of subsurface and surface vacancies is energetically preferred over full reduction of the surface or subsurface monolayer. The reduction of Cu2+ to Cu+ is found to be more favourable than that of Cu+ to Cu0 in the most stable vacancy structures at all concentrations. Consistent with the oxygen vacancy calculations, H2 adsorption occurs initially on under-coordinated surface oxygen. Water molecules are formed upon the adsorption of H2 and this gives a mechanism for H2 reduction of CuO to Cu. Ab initio atomistic thermodynamics shows that reducing CuO to metallic Cu at the surface is more energetically difficult than in the bulk so that the surface oxide protects the bulk from reduction. Using H2 as the reducing agent, it is found that the CuO surface is reduced to Cu2O at approximately 360 K and that complete reduction from Cu2O to metallic Cu occurs at 780 K

Modeling Mechanism and Growth Reactions for New Nanofabrication Processes by Atomic Layer Deposition

“…[ 86 ] To understand the role of reducing agents, we study how the surface of CuO is reduced to metallic Cu through oxygen vacancy formation or hydrogen adsorption. [ 87 ] On the basis of all these fi ndings, we propose metallocenes MCp 2 , where M(II) is an oxidisable transition metal cation, as possible reducing co-reagents for Cu ALD, and use quantum chemical calculations and solution phase experiments to evaluate the most promising metal M. [ 88 ] Phung et al contribute to the understanding of ALD of ruthenium in their DFT studies. [ 11,89 ] They study the adsorption of two different precursors, RuCp 2 and RuCpPy [Cp = C 5 H 5 , Py = C 4 H 4 N] on a TiN substrate using a vdW inclusive DFT method.…”

Stability and self-passivation of copper vanadate photoanodes under chemical, electrochemical, and photoelectrochemical operation

“…Formation of Cu 1+ can also be mediated by surface oxygen vacancies 16 and, if formed, may contribute to increased corrosion as the very mobile Cu 1+ ions are known to be less stable under high potential in aqueous conditions. Hence, exploring the change in surface speciation after photo-illumination is important.…”

Atomistic details of oxide surfaces and surface oxidation: the example of copper and its oxides

“…performed 92,108,109 . CuO (111) is the most stable surface also compared to defective CuO structures with surface and subsurface vacancies 108 , with surface energy γ = 0.74 J/m 2 (although much higher than the lowest energy Cu 2 O surface 77 ).…”