XPS and DFT Studies on the Autoxidation Process of Cu Sheet at Room Temperature

Abstract

To better understand the autoxidation mechanism of Cu-based catalysts, we studied the oxidation of Cu sheet exposed to ultrahigh vacuum and air at ambient temperature using X-ray photoelectron spectroscopy (XPS) and density functional theory. Six main stages of Cu autoxidation are revealed: (1) dissociative adsorption of O 2 , (2) coexistence of nondissociative and dissociative H 2 O adsorption, (3) diffusion of O and OH into Cu bulk, (4) formation of metastable Cu 2 O layer, (5) further oxidation and formation of metastable Cu(OH) 2 and CuO layer, and (6) transformation phase of the metastable Cu(OH) 2 to CuO. The formation of Cu(OH) 2 depends on the relative humidity of air and the concentration of adsorbed OH of the Cu sheet. On the basis of these results, we propose that the preservation time of the Cu-based catalysts should be decreased or the catalysts should be preserved in a high vacuum and at low relative humidity. Considering the time of the sample preparation before ex situ XPS analysis and other surface characterizations, the Cu-based catalysts need to be etched by ∼10 s using an Ar ion gun. These findings serve as a guide for the preservation and preparation of Cu-based catalysts before actual measurement.

Rapid fabrication of SERS substrate and superhydrophobic surface with different micro/nano-structures by electrochemical shaping of smooth Cu surface

“…Besides the stronger regular peaks at 934.74/954.49 eV attributed to CuO (Fig. 4c), there are several extra shake-up satellite peaks of Cu 2p 3/2 /Cu 2p 1/2 marked as"s1" and "s2" at 940.78/961.55 eV and 943.93/962.83 eV attributed to CuO (s1) and CuO (s2), which accord with previous reports [32,33]. While the difference in binding energy of Cu 2p between Cu 0 and Cu 2 O at 932.33/952.18 eV in Fig.…”

“…4d provides another means to identify the two valence states. The peaks at 570.02 eV and 568.04 eV are attributed to Cu 2 O and Cu 0 , respectively [32,33]. The Cu 2 O and CuO at the surface of coral-like copper film originated from inevitable surface autoxidation process of metal Cu in air [33].…”

A Non‐Noble Monometallic Catalyst Derived from Cu–MOFs for Highly Selective Hydrogenation of 5‐Hydroxymethylfurfural to 2,5‐Dimethylfuran

“…High‐resolution XPS spectra (Figure c and d) of Cu 2p 3/2 peak exhibited at ∼934.5 eV and the satellite peaks are the signature of Cu 2+ , which can be interpreted as the presence of CuO. The Cu + /Cu 0 peak also could be observed at ∼932.5 eV . The XPS survey draws a different conclusion with XRD result.…”

Photocatalytic hydrogen production from methanol aqueous solution under visible-light using Cu/S–TiO2 prepared by electroless plating method

“…3d) of EP and CR shifted to the higher energies (see Fig. 3d), indicating that there is an interaction between Cu species and TiO 2 surface atom, which is also the reason of the phenomenon that the Cu 2p 3/2 spin orbital splitting photoelectronic peak (932.6 and 933.7 eV to pure metallic copper and CuO [23], respectively) shifted to lower binding energy (at 930 eV and 932.1, see Fig. 3b).…”