Issue 47, 2015

A new look at oxide formation at the copper/electrolyte interface by in situ spectroscopies

Abstract

The widely used engineering material copper is a prototype of an electrochemically passive metal. In this work, the passive films on evaporated copper in 0.1 M NaOH are investigated in situ and operando by spectroscopic ellipsometry and Raman spectroscopy, both conducted during oxidation in potentiostatic step experiments. Oxide growth is initiated by jumping from a potential at which the surface is oxide-free to −0.1 V vs. Ag|AgCl|3 M KCl (+0.11 V vs. standard hydrogen electrode, SHE). At subsequent electrode potential jumps, no corresponding jumps in the thickness are observed; instead, oxide growth proceeds steadily. Above +0.3 V vs. Ag|AgCl|3 M KCl (+0.51 V vs. SHE), the oxide layer thickness remains constant at ≈7 nm. Raman spectra show a peak at 530 cm−1, which agrees with the dominant peak in spectra of copper mixed oxide, Cu4O3 (Cu2ICu2IIO3). Crystalline Cu4O3 nucleates from a precursor state showing strong photoluminescence (PL), which hints at the involvement of Cu2O. Overall, the PL spectra of the growing oxide and absorption spectra indicate the presence of Cu2O in the thin films. Absorption spectra cannot be understood as a superposition of the spectra from different well-described copper oxides, which points to defect-rich oxides that show rather different spectra. Raman spectra also point to an involvement of both crystalline and amorphous oxides that coexist. The results show that the passive layers on copper are more complex than the duplex layers described in the literature; they do contain an oxide with a mixed valency of copper.

Graphical abstract: A new look at oxide formation at the copper/electrolyte interface by in situ spectroscopies

Supplementary files

Article information

Article type
Paper
Submitted
29 Aug 2015
Accepted
02 Nov 2015
First published
02 Nov 2015

Phys. Chem. Chem. Phys., 2015,17, 31670-31679

Author version available

A new look at oxide formation at the copper/electrolyte interface by in situ spectroscopies

C. Toparli, A. Sarfraz and A. Erbe, Phys. Chem. Chem. Phys., 2015, 17, 31670 DOI: 10.1039/C5CP05172J

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