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

Maimaiti, Yasheng; Nolan, Michael; Elliott, Simon D.

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

Files

Maimaiti_Elliott_PCCP_16_3036_2014_submitted.pdf(1.38 MB)

Accepted Version

YM_ReductionAV2014_Add_File.pdf(837.47 KB)

Additional file: Supplementary Info

Date

2013-12-23

Authors

Maimaiti, Yasheng

Nolan, Michael

Elliott, Simon D.

Publisher

The Royal Society of Chemistry

Published Version

10.1039/C3CP53991A

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.

Keywords

Atomic layer deposition , Copper films , Electronic properties , Oxide reduction , Nickel oxide , Thin film , CuO , Density functional theory , DFT

Citation

MAIMAITI, Y., NOLAN, M. & ELLIOTT, S. D. 2014. Reduction mechanisms of the CuO(111) surface through surface oxygen vacancy formation and hydrogen adsorption. Physical Chemistry Chemical Physics, 16, 3036-3046. http://dx.doi.org/10.1039/C3CP53991A