Modulation of copper(I) oxide reduction/oxidation in atmospheric pressure plasma jet

Abstract

We describe the controlled reduction of copper(I) oxide films to metallic copper in a nonthermal, atmospheric pressure, helium plasma jet. Thin layers (≈ 0.1 m) of Cu2O are electrochemically deposited onto Pt electrodes and placed in capacitively coupled helium plasma doped with H2, O2 and CH4 gases. Ex-situ Raman spectroscopy was used to probe the effect of plasma treatment on the deposited copper oxide layer. We show that application of a static bias voltage to the Pt substrate during plasma exposure can control the rate of reduction of the copper(I) oxide film. We propose that the reduction process is mediated by plasma electrons and controlling the electron flux to the surface can be used as a means to modulate the reduction process.

Tarnished silver–copper surfaces reduction using remote helium plasma at atmospheric pressure studied by means of high-resolution synchrotron x-ray photoelectron microscopy

“…Plasma can supply the right ingredients to induce non-thermal electrochemical reaction in the gas/solid phase. The electrochemical reduction of Cu2O by atmospheric pressure plasma jets has been already shown even in absence of hydrogen [10]. In this condition, the reduction reactions which can occur in our experiment can be summarised as…”

“…The results obtained allowed to review the layered structure of the corroded layers at the sub-µm level, highlighting its evolution as a function of the corrosion process and the following plasma cleaning stage. In addition, this improved description of the surface evolution permitted to suggest an extension of the electrochemical metal oxides reduction mechanism introduced in the electronics field [10] to Ag,Cu sulphides. The proposed model highlights the complementary action of hydrogen atoms and electrons for silver sulphide and copper monosulphide reduction and explains the unsuccessful result on Cu2S.…”

“…However, as a remote plasma configuration is used, where plasma density close to the sample surface is an order of magnitude lower than between the electrodes, the reduction process is still preforming on CuO but dramatically slowed down for Cu2O [9]. In addition, the reduction process on copper oxide was observed also in absence of hydrogen, suggesting that not only the hydrogen atoms are involved but also plasma electrons [10]. Following this intuition, the combined use of hydrogen and free electrons to trigger electrochemical reactions were tested for surface patterning applications using plasma jet on metal oxides films [11].…”

Patterning of metal oxide thin films using a H2/He atmospheric pressure plasma jet

“…16 We have shown that helium plasma at atmospheric pressure in the absence of hydrogen was effective at reducing copper oxide films, suggesting that electrons alone are, in the case of copper, sufficient for the reduction process. 17 This view is supported by Lee et al 18 and Sui et al 19 who loaded metal ions in a polymer matrix and showed using an APPJ that the reduction of the metal ions was indeed driven by plasma (or secondary) electrons.…”

“…We know from plasma exposure of copper oxide that hydrogen (radical or otherwise) was not necessary for the reduction process, but speeds up the reduction process. 17 Therefore, the excited electrons (either plasma or secondary electrons) are key for the reduction process.…”