Polarization curves in the ohmic controlled electrodeposition of metals

The conditions under which ohmic controlled metal electrodeposition occurs are discussed using a simple mathematical model. it is shown that ohmic controlled electrodeposition can be operative if the value of the exchange current density for the electrodeposition process is more than 10 times larger than the corresponding value of the limiting diffusion current density. In this case, a linear dependence of the current density on overpotential up to the value of the limiting diffusion current density can be observed. On the other hand, the initiation of dendrite growth under these circumstances is possible, even at very low values of overpotential, at the moment when the limiting diffusion current density is attained in potentiostatic electrodeposition. In this way, instead of a limiting diffusion current density plateau. an inflection point on the polarization curve can be observed, since dendritic growth is followed by an increase in the deposition current density. At the same time. it is shown that the ensemble of tips of dendrites can behave as an ensemble of microelectrodes working independently under mixed or activation control due to the absence of a common diffusion layer. This was confirmed by deposition of copper on a copper dendritic electrode and by silver electrodeposition from a silver nitrate solution onto a graphite substrate. (C) 2008 Elsevier Ltd. All rights reserved.