The kinetics of mercury nucleation from Hg2+2 and Hg2+ solutions on vitreous carbon electrodes

The kinetics of the electrochemical nucleation of Hg onto Vitreous carbon were studied from analysis of potentiostatic current transients obtained at different overpotentials in Hg-2(2+) and Hg2+ solutions. Similar sizes of critical nuclei and number densities of sites on the surface were found for nucleation of Hg from both solutions, indicating, in agreement with nucleation theory, that the rates of nucleation are controlled by surface energies and deposit-substrate interactions. Saturation number densities of nuclei were deduced from the kinetic analysis, and their relationship with those obtained from direct observation of the electrode surface is discussed. It was found that at low overpotentials, the nuclei deposited from both solutions were uniformly distributed on the electrode surface, whereas their distribution was affected by inhibition of the nucleation rates close to already established nuclei at high overpotentials. This inhibition was enhanced during deposition from Hg2+ solution. (C) 1999 Elsevier Science S.A. All rights reserved.