A kinetic description of Pd electrodeposition under mixed control of charge transfer and diffusion

This work evaluates the kinetics of Pd nanoparticles nucleation and growth at the potential range where electrodeposition is controlled by both charge transfer and diffusion. For this purpose, Pd electrodeposition from an aqueous solution containing PdCl2 (0.001 M) and H2SO4 (0.5 M) was studied by means of cyclic voltammetry and potentiostatic current–time transients (CTTs). Using the polarization curves, regions corresponding to charge transfer control, mixed control and diffusion control were identified. In mixed control region, CTTs study suggested the presence of three processes involving adsorption, the ion transfer reaction and 3D progressive nucleation with mixed charge transfer-diffusion controlled growth. The kinetic parameters at different electrode potentials within the mixed control region were estimated through the analysis of CTTs at short times in accordance with the model proposed by Milchev and Zapryanova. It was found that the reduction reaction of Pd(II) → Pd(I) – as an ion transfer reaction – occurs before the formation of Pd nucleus and its corresponding ion transfer coefficient was estimated αi = 0.33.