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 (Cu2(I)Cu2(II)O3). 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.

In situ spectroscopic monitoring of CO2 reduction at copper oxide electrode

“…that for (a), so the noise due to adventitious water vapour at 1400 -1800 cm -1 is much more pronounced in (a). In the absence of CO2 and with application of -0.4 V (Fig 7 a), gains in absorbance 5 are seen at 1635, 1362, 1012 and 845 cm -1 corresponding to bands for bicarbonate, which are slightly shifted to higher wavenumber than reported for the solution anion 30 . This increase in bicarbonate concentration on application of -0.4 V suggests that the applied potential encourages surface adsorption of the anion.…”

“…All of the readily available metals 3 , many metal alloys 4 , oxides 5 and sulphides 6 have been investigated as electrodes for CO2 reduction. The most promising and widely studied material is copper, as it the only metal to produce 30 hydrocarbons and appreciable quantities of >C1 products during CO2 reduction 7 . However, problems persist with poor faradaic efficiency (due to the competing H2 evolution reaction), poor product selectivity and loss of activity over time.…”

State of the Surface of Antibacterial Copper in Phosphate Buffered Saline

“…Copper ion release from the metal, and oxide film formation in biological test solution, are accepted to be the key for bacteria killing. 1,4,12,13 While a number of works are available addressing the surface film formation on copper in alkaline electrolytes, [14][15][16][17] much less physicalchemical data is available for conditions when active corrosion is possible, 18 and to our knowledge, the state of the surface during electrochemical polarization in a biochemical buffer has not been investigated. However, a number of reactions are possible in the typical biochemical buffers, in addition to those present in usual aqueous electrochemistry.…”

“…The film formation at the copper|electrolyte interface in general has been characterized by coupling electrochemical experiments to in situ characterization methods. [15][16][17] In situ Raman spectroscopy studies showed the potential dependent oxide formation. 18,35 Using their vibrational fingerprints in Raman spectroscopy, three main oxide phases of Cu can be easily identified.…”

“…[20][21][22] In a previous study, we showed that the formation of Cu 4 O 3 occurs during the oxidation of Cu in alkaline environment. 17 The interactions of copper oxides with complexing ions such as Cl − are rather complicated. 7,[23][24][25][26] Consequences of such interaction may be a localized attack, with loss of the oxide film.…”