Research and Development Techniques 1: Potentiodynamic Studies of Copper Metal Deposition

The electrochemistry of copper (II)/(I) ions in aqueous chloride solution, at pH2, is used to demonstrate the application of voltammetry techniques in characterising electrode processes. The electrolyte used is 1.5 M sodium chloride containing 20 to 50 × 10^?3 M cupric chloride at 20°C, in which both Cu(II) and Cu(I) ions are stable. A platinum rotating disc electrode (RDE, radius 0.365 cm) is used to provide controlled mass transport under laminar flow conditions. Cyclic voltammetry, at a stationary disc electrode, is used to characterise the general electrochemistry. Four current peaks due to reduction of Cu(II) ions to Cu(I) ions, deposition of Cu from Cu(I) ions, anodic stripping of Cu to form Cu(I) ions and oxidation of Cu(I) ions to Cu(II) ions are seen. Analysis of the Cu(II)/Cu(I) couple indicates a reversible process. A potential sweep rate experiment allows the diffusion coefficient of Cu(II) ions to be calculated. The anodic stripping peak in the cyclic voltammogram is used to estimate the amount of copper deposited. Reduction of Cu(II) to Cu(I) then to Cu is examined at a range of rotation speeds (150–1870 rpm) using linear sweep voltammetry at the RDE. Mass transport data are obtained in the form of limiting current density as a function of the RDE speed, allowing the diffusion coefficients of Cu(II) and Cu(I) ions to be calculated.