EQCM study on the oxidation/reduction of bismuth sulfide thin films

The oxidation/reduction of bismuth sulfide thin films deposited on an Au electrode using the successive ionic layer adsorption and reaction method has been investigated by electrochemical quartz crystal microbalance combined with cyclic voltammetry and X-ray photoelectron spectroscopy. It has been shown that the oxidation/reduction of bismuth sulfide film depends on the nature of anion. In the acetate solution the bismuth sulfide film is oxidized at more negative potential values than that in sulfuric acid solution. During the oxidation of bismuth sulfide film the Bi present on the surface of the bismuth sulfide film is oxidized first. This process is followed by subsequent oxidation of bismuth sulfide film alongside the oxidation of Au. In the acetate background solution the oxidation of bismuth sulfide occurs with the whole film stripping and the calculated amount is related to the amount of deposit and corresponds to the thickness of ∼9–10 nm. In sulfuric acid the bismuth sulfide film is not completely stripped out in one anodic cycle. The evaluated amount during the first anodic scan corresponded to the thickness of deposit of ∼3–4 nm. The reduction of bismuth sulfide film took places at more positive potential values in the acetate background solution than that in sulfate background solution at pH 4. After the reduction of bismuth sulfide film to Bi0 and S2− in the background solution, depending on the nature of anion, the oxidation of metallic Bi proceeds by two different mechanisms: in the sulfate solution Bi is oxidized to Bi(III) oxygen compounds while in the acetate solution Bi is oxidized by dissolution.