Study of the electrodeposition of rhodium on polycrystalline gold electrodes by quartz microbalance and voltammetric techniques

The electrodeposition of rhodium on different polycrystalline gold substrates from Na3RhCl6.O12H2O + NaCl solutions was investigated by electrochemical quartz crystal microbalance and voltammetric techniques. A study of the electrodeposition of rhodium from the concentrated chloride solutions used in this work show several features that are associated with potentiostatic transients with growth of the clusters controlled by mixed kinetics, charge transfer and diffusion. The results in this paper offer a clear warning against the blind interpretation of potentiostatic transients with models based on simple diffusion controlled growth. At low overpotentials the electrodeposition of rhodium is characterized by very slow charge transfer kinetics and starts with the formation of a submonolayer. Even at more negative potentials current transients and massograms recorded at constant potential exhibit an apparent induction time, indicating that growth initially is controlled by mixed kinetics, charge transfer and diffusion. Bulk deposition of rhodium is shifted to more negative potentials compared with other solutions, e.g., H2SO4-based electrolytes, but the exact influence of rhodium speciation in the plating solutions remains unknown. (C) 2004 The Electrochemical Society.