The Role of Cu(I) in the Process of Forming Cu2–xS Coatings by a Chemical Route

Abstract

The interaction of the Cu 2 O adsorbed with Na 2 S n (n = 1-4 ), during formation of the Cu 2-x S coatings has been investigated by cyclic voltammetry. The summarized reaction of this process has been shown to correspond to the equation: Na 2 S + Cu 2 O ad + H 2 O → Cu 2 S ad + (n-1)S 0 + 2NaOH, where S 0 /Cu=(n 1)/2. Such a stoichiometry of reaction ca be explained by the formation of an intermediate the adsorbed polysulphide of Cu(1) and by its subsequent decomposition into Cu 2 S and S 0 . When a thicker coating is being formed, i.e., when the surface being coated is repeatedly immersed into an ammoniate solution of Cu (1) and S 0 fully bounded: S 0 ad + 2Cu + → CuS + Cu 2 + . At the same time due to different solubility products (L=2.5-10 and 6.3-10 for Cu 2 S and CuS respectively), an exchange CuS ad + 2 (1-x)Cy + →Cu 2-x S ad +(1-x)Cu 2+ occurs. After formation of Cu 2+ . parallel processes characteristic for the interaction of Cu(II) with Na 2 S n start to take place, during which S is also formed.