The paper discusses results on the nucleation (electrocrystallization) of nickel oil an assembly of carbon microelectrodes and its electrocatalytic activity in the hydrogen evolution reaction. It has been shown that within an appropriate potential range the nickel electrocrystallization follows a three-dimensional progressive nucleation and diffusion controlled stable cluster growth. Analysis of the experimental current transients has been carried out using a modified form of the Scharifker and Mostany equation that considers only the relevant part of the current density response. A set of kinetic and then nodynamic parameters has been determined: the nucleation rate. the number of atoms in the critical nucleus. the diffusion coefficient, and the Gibbs energy of nuclei formation. Ac and de measurements oil hydrogen evolution in an alkaline solution have demonstrated an increased electrocatalytic activity of the nanostructured Ni layer on carbon microelectrodes in the hydrogen evolution reaction in comparison to a bulk nickel electrode. (c) 2006 Elsevier B.V. All rights reserved.