DEPENDENCE ACTIVATION ENERGY OF THE ELECTROREDUCTION OF PALLADIUM(II) BIS-HYDROXYETHYLIMINODIACETATE COMPLEXES ON THE OVERPOTENTIAL

Abstract

The kinetic (exchange currents, apparent elect-ron transfer coefficients) and energetic (activation energies of diffusion and electron-transfer reaction) parameters of electroreduction of palladium (II) bis-hydroxyethyliminodiacetate complexes from an ele-ctrolyte containing an excess of free ligand have been determined. A method is proposed for calculating the actual activation energy of the electrode process that is controlled by mixed kinetics, based on the dif-fusion activation energy, transition reaction and the ratio of surface and volume concentrations of potenti-al-determining ions in the solution under study or the ratio of the limiting diffusion current jd and dischar-ge current jk of palladium (II) hydroxyethyliminodi-
 
 acetate complexes. The actual activation energy Af of the electrode process, which is controlled by mixed kinetics, is calculated based on the diffusion activati-on energy, transition reaction and the ratio of the li-miting diffusion current jd and discharge current jk of palladium (II) bis-hydroxyethyliminodiacetate com-plexes. The contribution of the activation energy of the transition stage (slow discharge) and the diffusion activation energy of bis -hydroxyethyliminodiacetate palladium (II) complexes to the actual activation ener-gy of the electrode process limited by mixed kine-tics is determined. The dependence of actual activation energy on electrode process overpotential has been stu-died. The actual activation energy Af of the electro-de process varies from the value of the activation ener-gy of the transition reaction At (63.4 kJ×mol–1) to the value of the diffusion activation energy Ad (22.5 kJ ×mol–1). The activation energy calculated according to Tyomkin can be considered as the actual activation energy Af of the discharge stage at a given polarizati-on DE only with a purely kinetic control of the pro-cess rate. The activation energy experimentally deter-mined by the temperature-kinetic method according to the Arrhenius equation and calculated by the pro-posed method is the actual activation energy Af of the electrode process, controlled by mixed kinetics. There is a coincidence of the experimentally determi-ned by the Gorbachev method and the actual Af acti-vation energy of electrode process controlled by mi-xed kinetics calculated by the proposed method. A good agreement between the calculated and experi-mentally determined values of the actual activation energy of the electrode process is observed.