Saturation nucleus density in the electrodeposition of metals onto inert electrodes II. Experimental

Abstract

The number of nuclei grown as a function of time, overpotential and eletrolyte concentration have been investigated experimentally during the electrodeposition of Hg from an aqueous solution of Hg 2(NO 3) 2 onto a plane structureless platinum electrode and a hemispherical single-crystal electrode. It has been established that: (i) at constant overpotential after an induction period the number of nuclei grows linearly with time and reaches a saturation value after a sufficient time has elapsed; (ii) the higher the overpotential the shorter the induction period and the higher both the steady state nucleation rate and the saturation nucleus density; (iii) the smaller the electrolyte concentration the lower the nucleation rate, the longer the induction period and the larger the saturation nucleus density. It is shown that the time dependence of the number of nuclei can be described by an equation derived by assuming that nuclei are formed on active energetically preferred sites on the electrode surface, and that the saturation nucleus density is determined by the deactivation of the active centres by overlapping nucleation exclusion zones. Experimental data confirming the idea of Mutaftschiew and Toschev that the active centres are defects in the oxide layer covering the platinum are presented.