During cementation of Ni2+ ions onto a zinc electrode, the time-dependence of the concentration of Ni2+ ions was studied by atomic absorption spectroscopy. The electrode surface was analyzed by S.E.M. and the surface area was measured by electrochemical impedance spectroscopy. The cementation is shown to be a first-order reaction which is diffusion-controlled. The reaction rate is strongly affected by the increase in the electrode surface area with increasing cementation time.