The electrochemical and chemical reactions occurring at a platinum electrode immersed in an Na2S solution were investigated by cyclic voltammetry and controlled-potential electrolysis. It was found that the HS- ions were oxidized in two stages; the first one was the process of oxidizing the hydrosulphide ions into intermediate polysulphite ions, and the second was the further oxidization to elemental sulphur. The formation of a sulphur film significantly reduced the rate of electrolysis. The chemical dissolution of this film was found to mitigate the electrode blocking effect.