Electrocatalytic Reduction of Peroxodisulfate in 0.5 M NaOH at Copper Electrodes. A Combined Quartz Microbalance and Rotating Ring/Disc Electrode Investigation

From an electrochemical investigation by means of an electrochemical quartz microbalance, a rotating disc electrode, and a ring/disc electrode, two mechanisms for the reduction of S 2 O 8 2- became apparent. Besides the well-known outer-sphere cathodic reduction, a catalytic mechanism of S 2 O 8 2- reduction operates in a potential range between the surface oxide region (≈−0.5 V/SCE) and −1.0 V/SCE. It involves the chemical oxidation of the copper surface to a soluble Cu(I) species. The catalytic mechanism is concluded to result from the specific interaction between S 2 O 8 2- and the Cu surface modified by the presence of subsurface oxygen.