Electrochemical behavior of In-DTPA complexes: anodic dissolution, cathodic reduction, and electrochemical nucleation

In this paper, the influence of a chelating agent-diethylenetriaminepentaacetic acid (DTPA) on the anodic dissolution and cathodic deposition of indium was studied using electrochemical impedance spectroscopy (EIS), linear polarization (LP), and cyclic voltammetry (CV). Electrochemical impedance measurements demonstrate that the equivalent electrical circuit of the electrode/electrolyte interface includes both the Gerischer impedance and Warburg impedance, which explains the quasi-reversible kinetics, and the reaction mechanism is chemical-electrochemical. Results of linear polarization and impedance measurements demonstrate the decrease in polarization resistance of anodic dissolution of indium from 1.02 to 0.73 k Omega cm(2) in the presence of DTPA in an alkaline medium. The activation energy of indium electrodeposition from the DTPA-containing electrolyte was determined from EIS data, demonstrating sluggish kinetics of the reaction, and the value of the activation energy was 62.1 kJ mol(-1). Moreover, the high overpotential of indium electroreduction was confirmed by the decrease in the diffusion coefficient of indium ions from 2.9 x10(-7) to 1.4 x10(-7) cm2 s(-1) in the presence of DTPA. The dimensionless current transients of indium electroreduction on platinum electrode show both instantaneous and progressive nucleation mechanisms depending on the applied potential, according to the Scharifker-Hills 3D nucleation model. The nucleation density and nucleation rate were 7.91 x 10(7) cm(-2) at - 1.425V and 4.87 x 10(9) cm(-2) s(-1) at an applied potential of - 1.450 V, respectively. The results of this study may be useful for the electrochemical recovery of indium from indium tin oxide (ITO) waste.