Topographic changes of polycrystalline Ag and Cu electrodes in acid aqueous solutions resulting from a prolonged application of the potential reversal technique

The electrochemical faceting and roughening of polycrystalline Ag and Cu electrodes in aqueous 0.01 M HClO4 + 0.5 Pd NaClO4 at 25 degrees C was investigated by applying a symmetric square wave potential reversal technique for 20 h between preset upper and lower potential values in the range 5 Hz < f < 5 kHz. The characteristics of treated specimens were followed by voltammetry, Ph underpotential deposition for Ag, and T1 underpotential deposition for Cu, and scanning electron microscopy. For f < 50 Hz, the net electrochemical reaction involves the metal electrodissolution in the oxidation half-cycle and metal electrodeposition accompanied by the development of a branched metal topography in the reduction half-cycle. In contrast, for f > 50 Hz, the metal electrodissolution/electrodeposition cycling produces local faceting at each metal grain. The amount of soluble species found in the solution after a 20 h potential reversal technique increases as f is decreased. Under comparable conditions, both metals behave in a rather similar way, although Cu deposits are always more compact than those resulting from the application of the potential reversal.