Voltammetry and multistep chronoamperometry-voltammetry experiments have been conducted to study the inhibition of Cu2+ reduction on a copper substrate in the presence of Cl- and poly (ethylene glycol) (PEG). Among the aspects investigated is the dynamics of inhibiting film formation from the change in current as PEG and Cl- are added at fixed potential. The effect of the additives is slow acting and relatively small at concentrations below where PEG completely covers the substrate but becomes large and rapid when the substrate becomes completely covered and Cu2+ reduction is strongly inhibited. The hysteresis observed in cathodic scans at intermediate PEG and Cl-concentrations is shown to arise largely due to the slowness with which the inhibiting film is restored after its removal during the forward scan. Furthermore, the restoration of the film is found to be much slower than the process by which it first forms. Multistep experiments indicate that PEG can adsorb in the presence of Cl- in a Cu2+- free solution, but does not strongly inhibit deposition when subsequently immersed in a CuSO4 solution. Only when Cl- and PEG are present in the solution where Cu2+ is being reduced is strong inhibition observed. (c) 2008 The Electrochemical Society.