Determination Of The Composition
DETERMINATION OF THE COMPOSITION
OF ELECTROCHEMICALLY ACTIVE COMPLEXES
ON AN ELECTRODE
V.S. Kublanovsky
Institute of General and Inorganic Chemistry, Ukrainian National Academy of Sciences, Palladina avenue 32-34, 03680 Kiev-142, Ukraine,
e-mail: kublanovsky@ionc.kar.net
One of the most important problems of modern electrochemistry is the elucidation of the mechanism electrode processes and chemical stages which accompany the formation of electrochemically active complexes (EAC) on an electrode.
The present-day concepts of the discharge of coordination compounds are based on the fact that complex ions which differ in composition from complexes predominating in the bulk electrolyte react generally on the electrode.
The usual methods for determining the composition of electrochemically active complexes are based on the fact that only one complex in equilibrium with the complex that is dominant in the bulk of the electrolyte is discharge on the electrode. It is evident that the overwhelming majority of electrochemical system are characterized by quite a number of complex compounds in the bulk of the electrolyte and in the electrode layer. It is also quite logical to think that metal ions are discharged from all or several ionic species that are present in
the bulk of the electrolyte or are formed in the cathode layer and on the electrode surface in a particular case, a single species may be such an electroactive species.
We have developed methods for determining electroactive ionic species on the basis of the method developed earlier for determining all concentrations on the electrode surface. New electrochemical functions are proposed: "discharging ion complexity", which relates formation constants to electrode reaction parameters, and "average coordination number of discharging ion", which indicates the composition of discharging complexes.
The study of equilibria in the bulk electrolyte and in the cathode layer as a function of the ratio of the main solution components, pH and polarizing
current density in conjunction with electrochemical parameters makes it possible to establish, by using the proposed theory, the composition of EAC’s that are directly involved in the electrode reaction during the reduction of complexes and hence to control electrochemical processes.
The proposed theory and methods permit one, unlike conventional ones, to investigate electrochemical systems containing no excess ligand (ligands) when several complex metal compounds are present in the electrolyte in comparable amounts and one or several electroactive complexes are directly involved in the electrode process.
Method for determining electrochemically active and electrochemically inactive ions are shown for the discharge of cadmium, zinc and cooper coordination compounds with complexones and halide ions.
References
1. V. Kublanovsky and V. Belinsky, J. Electroanalyt. Chem., 383(1995) 85.
2. V. Kublanovsky and K. Litovchenko, J. Electroanalyt. Chem., 495(2000) 10.
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