Extracting nucleation rates from current–time transients: Part III: nucleation kinetics following the application of a pre-pulse

An appropriate model for the clectrocrystallisation processes, following the application of a pre-pulse of large amplitude and short duration, is proposed. This model, contrary to common belief, is based on the assumption that nucleation sites are not permanently converted into nuclei at the pre-pulse, but, rather, that with the application of the second potential the embryos (nuclei, unstable at the second potential) dissolve, allowing a number of sites, hitherto occupied, to become again available. Furthermore, at the second potential, electrocrystallisation is not characterised by the process of growth only, but re-nucleation at the new sites (which since the dissolution of the embryos, have become available) also occurs in addition to the growth of the stable nuclei formed at the pre-pulse. The transient equation derived on the above basis is shown to fit closely the behaviour of the recorded prepulse transients for the clectrocrystallisation of nickel onto a vitreous carbon electrode. It is shown that a significant number of nuclei formed during the application of a pre-pulse of −1.5 V for 20 ms have not attained the size required for growth at the deposition potential and gradually dissolve only to be re-nucleated immediately and grow. Concerns raised in the conclusions of the previous paper have been adequately addressed by the new model.