SUMMARY
The interaction of the Cu2O adsorbed with Na2Sn (n = 1–4), during formation of the Cu2–xS coatings has been investigated by cyclic voltammetry.
The summarized reaction of this process has been shown to correspond to the equation:
Na2Sn + Cu2Oad + H20 → Cu2Sad + (n–1)So + 2NaOH,
where So/Cu=(n–1)/2. Such a stoichiometry of reaction can be explained by the formation of an intermediate—the adsorbed polysulphide of Cu(I)—and by its subsequent decomposition into Cu2S and So.
When a thicker coating is being formed, i.e., when the surface being coated is repeatedly immersed into an ammoniate solution of Cu(I) and So fully bounded:
Soad + 2 Cu+ → CuS + Cu2+.
At the same time due to different solubility products (L=2.5·10−48 and 6.3·10−36 for Cu2S and CuS respectively), an exchange
CuSad + 2(1–x)Cu+ → Cu2–xSad+ (1–x)Cu2+ occurs.
After formation of Cu2+, parallel processes characteristic for the interaction of Cu(II) with Na2Sn start to take place, during which So is also formed.