Analysis of Rhodium Electrodeposition from Chloride Solutions

The work presents studies of the mechanism and kinetics of rhodium(III) complexes electro-reduction in chloride solutions at pH = 3. The studies were preceded by the thermodynamic analysis of the electrolyte. Electrochemical examinations were performed with the use of cyclic voltammetry (CV) combined with electrochemical quartz crystal microbalance (EQCM) and electrochemical impedance spectroscopy (EIS). The M/z values determined during electrogravimetric measurements indicate that reduction process of aquachloro- rhodium(III) complexes occurs in one step due to 3-electrone irreversible reduction reaction. Results of voltammetric as well as EIS tests indicated that Rh deposition occurs in both underpotential (UPD) and overpotential (OPD) range. The examined reactions were diffusion controlled. Diffusion coefficient of RhClx(H2O)6 − x]3 − x (x = 4, 5, 6) was determined with the use of Berzins-Delahay equation and amounts at 3.65 · 10− 6 [cm2/s].