Naslov
Kinetics and mechanism of electrocrystallyzation in oxide matrix

Autori
Grubač, Zoran ; Metikoš-Huković, Mirjana,

Izvornik
Electrochimica Acta (0013-4686) 44 (1999), 25; 4559-4571

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
bismuth-oxide films; electrocrystallyzation; nucleation; potentiostatic cathodic current transients; electrode kinetics

Sažetak
The kinetics and mechanism of cathodic decomposition of potentiodinamically formed Bi_2O_3 layer in a borate buffer solution, pH = 9.2, were studied in-situ using cyclic voltammetry, potentiostatic transient and electrochemical impedance spectroscopy (EIS) techniques. The electrocrystallyzation of bismuth in the matrix of the oxide film occurred by injection of electrons from the underlying metal into the film/electrolyte interface. Impedance spectra demonstrated that the film/electrolyte interface had a close-to-perfect RC feature, because of intrinsically good electronic conductivity of bismuth oxide. Potentiostatic current-time transients revealed more details of the reduction process, giving further insight into the mechanism of reductive decomposition of Bi_2O_3 up to metallic Bi. The initial stage of reductive decomposition of Bi_2O_3 at relatively low cathodic potentials (close to the reversibile potential of the Bi_2O_3 /Bi couple) was described by equations valid for progressive nucleation and 3-D growth mechanism under charge transfer control. At higher negative potentials, where the metal phase segregation (deposition) took place, the electroreduction was described by a complex equation which included progressive nucleation and 3-D growth mechanism under charge transfer control, as well as instaneous nucleation and 2-D growth mechanism controlled by diffusion of redissolving OH^- ions away from the reacting interface. Local increase in pH at the interface from pH=9.2 up to pH=11.14, during diffusion stage of OH^- ions resulting from the electroreduction process, the density of nuclei instantaneously formed (N_o), the rate constant of crystal growth parallel to the electrode surface (k_1), and the roughness factor (sigma), have been determined.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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