The effect of pulsating potential on the morphology of metal deposits obtained by mass-transport controlled electrodeposition

Abstract

Experiments have been carried out on the deposition of copper and zinc by imposing pulsating cathodic overpotentials of varying frequency on the electrodes. In the potential region, where the resulting currents were large enough to produce complete concentration polarization at the electrode, it was shown that at very low frequency (t~10 cps) deposits exhibited surface roughness increasing with time in a manner similar to that seen in d.c. deposition. With increasing frequency an ever smoother deposit was obtained, and at high frequencies (≈ 10,000 cps) no increase in surface roughness could be noted. A theory has been developed for reversible electrodes ascribing this effect to the capacity of the pulsating potential to give an effective diffusion layer of constant thickness determined primarily by the frequency. At very high frequencies the diffusion layer is thin and follows the micro-profile of the surface so closely that the diffusion flux and the resulting deposit are even and no surface irregularity is amplified.