engleski

ELECTRODEPOSITION OF BISMUTH ONTO GLASSY CARBON AND GRAPHITE ELECTRODES FROM NITRATE SOLUTIONS

Glassy carbon (GC) exhibits a rather high chemical inertness and a rather low oxidation rate which, together with very small pore sizes and a small gas and liquid permeability, makes it a convenient inert electrode. It is known that the activity of the glassy carbon electrodes depends on the properties of the glassy carbon examined, the temperature and thermal treatment as well as the mechanical and electrochemical pretreatment of the sample. For preparing and activating the glassy carbon electrode surface different pretreatments have been widely discussed, like mechanical treatment, laser treatment, irradiation of glassy carbon with ultrasound, electrochemical treatment, etc. [1] In this work the kinetics and mechanism of cathodic electrodeposition of bismuth on glassy carbon (GC) and carbon electrodes were studied using cyclic voltammetry and chronoamperometry. As electrolyte the deaerated nitrate solutions c(HNO3) = 0.5 mol dm-3 with different concentrations of Bi3+ (concentration range from 20 mM to 0.5 mM) ion were used. Experiments were performed on AUTOLAB PGSTAT 302N, controlled by PC in standard three-electrode cell with platinum electrode as counter electrode and saturated calomel electrode (SCE) as reference electrode at the temperature 25oC. The electrochemical activation of electrodes was performed by continuously cycling in deaerated 0.5 M HNO3 solution in the potential range between the hydrogen and oxygen evolution. Cyclic voltammograms of GC electrode in 0.5 M HNO3 solution with the presence of Bi3+ ion showed a couple of well defined cathodic and anodic peaks and a crossover between the cathodic and anodic branches. The presence of the crossover is diagnostic for the formation of bismuth nuclei on the GC electrodes. The potentials of the cathodic deposition and the anodic dissolution of bismuth depend on concentration of Bi3+ ion in the electrolyte. The initial stage of bismuth electrodeposition was studied using potentiostatic pulse technique. The potentiostatic pulses were performed from the potential 290 mV to the various formation potentials in the range of bismuth nucleation and growth. The shape of the obtained transients is typical for the nucleation and growth of deposits on a conducting surface. As the transient potential (Et) shifts to the cathodic side, the current maximum (jm) increases, while the corresponding time maximum (tm) decreases. The potentiostatic transients were normalized according to the current maximum and time maximum values and compared wit the theoretical curves for two and three dimensional nucleation and growth under diffusion control. Through the applications of relations which hold true for such a nucleation model the following parameters were determined: the cathodic nucleation potential (ECN), the rate of nucleation (AN∞ ), the diffusion coefficient (D) and the density of growing sites (Ns). The results obtained at different carbon electrodes were discussed.

Electrodeposition; Bismuth; Nucleation; Glassy carbon;

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