The role of Cu(II) in the process of forming non-stoichiometric copper sulphide coatings by a chemical route

The composition of non-stoichiometric copper sulphide (Cu2-xS) coatings obt ained during the interaction of Cu(II) with Na2Sn (n = 1-4) has been invest igated by cyclic voltammetry in 0.05 M H2SO4 solution. The overall reaction has been shown to correspond to the question: 4 Na2Sn + 2 Cu(OH)(2ad) --> Cu2Sad + (4n-3) S(ad)degrees + 4 NaOH + 2 Na2S in which S degrees/Cu = (4n-3)/2. Such a stoichiometry of reaction has been explained by the formation of an intermediate - the adsorbed Cu(II) polysulphide (Na2CuSn) or a polynuclear complex (Na2Cu2S2n) - and its decomposition in simultaneous intramolecular redox reaction between Cu(II) and S2-. When increasing n from 1 to 4, (2-x) increases from 1.91 to 1.99 approximat ely.