Calculations of oxide formation on low-index Cu surfaces

Abstract

Density-functional theory is used to evaluate the mechanism of copper surface oxidation. Reaction pathways of O2 dissociation on the surface and oxidation of the sub-surface are found on the Cu(100), Cu(110), and Cu(111) facets. At low oxygen coverage, all three surfaces dissociate O2 spontaneously. As oxygen accumulates on the surfaces, O2 dissociation becomes more difficult. A bottleneck to further oxidation occurs when the surfaces are saturated with oxygen. The barriers for O2 dissociation on the O-saturated Cu(100)-c(2×2)-0.5 monolayer (ML) and Cu(100) missing-row structures are 0.97 eV and 0.75 eV, respectively; significantly lower than those have been reported previously. Oxidation of Cu(110)-c(6×2), the most stable (110) surface oxide, has a barrier of 0.72 eV. As the reconstructions grow from step edges, clean Cu(110) surfaces can dissociatively adsorb oxygen until the surface Cu atoms are saturated. After slight rearrangements, these surface areas form a "1 ML" oxide structure which has not been reported in the literature. The barrier for further oxidation of this "1 ML" phase is only 0.31 eV. Finally the oxidized Cu(111) surface has a relatively low reaction energy barrier for O2 dissociation, even at high oxygen coverage, and allows for facile oxidation of the subsurface by fast O diffusion through the surface oxide. The kinetic mechanisms found provide a qualitative explanation of the observed oxidation of the low-index Cu surfaces.

Selectivity Control of Cu Nanocrystals in a Gas-Fed Flow Cell through CO2 Pulsed Electroreduction

“…Prior literature reports revealed that differently oriented Cu surfaces display different oxidation kinetics. 38 , 39 Our {100} nanocubes are transformed during the pulse electrolysis into rougher morphologies with likely distinct oxidation dynamics. While extrapolation of the results collected with 60 s pulses to the case with 1 s pulses should be done with caution, in both cases we observe very similar trends in the sense that the role of the periodically regenerated oxide species diminishes with time, in line with the irreversible changes previously revealed.…”

Highly reversible oxygen redox in layered compounds enabled by surface polyanions

“…At this point, the reverse process in the discharged state, which requires O 2 dissociation and Mn extraction, becomes kinetically prohibitive. We did not calculate the barrier for the reverse process, but it is well known that O 2 dissociation on oxides is kinetically hindered at room temperature 35,36 . Consequently, O 2 release is the detrimental factor for reversibility.…”

Plasma-assisted oxidation of Cu(100) and Cu(111)

“…In previous studies, a mismatch of 17.5% has been estimated between the two unit cells, taking into consideration that the Cu 2 O(111) surface unit cell is 2.35 times larger than the one of Cu(111). 48 For oxidation treatments longer than 10 s in 4 Â 10 À4 mbar O 2 , the LEED patterns do not show substrate spots anymore, but the quasi (2 Â 2) superstructure with the hexagonal orientation corresponding to the ongoing growth of the Cu 2 O(111) and CuO(111) lms. However, on the Cu(100) crystal, the LEED pattern is composed of 12 equally distant diffuse spots superposed to an inner smaller diffuse ring.…”