engleski

A Study of Surface Layers by Photopolarization and Electrochemical Impedance Spectroscopy

In this work, we report a study of the electronic and dielectric properties of anodically grown Bi(III)oxide under potentiostatic and potentiodynamic conditions. Spectroscopically pure Bi disc (Johnson-Matthey), with a roughness factor of 1.8, was used as the working electrode. All experiments were carried out in a Na-borate buffer solution, pH=9.2, using the electrochemical set-up consisting of a potentiostat/galvanostat and a Lock-in Amplifier, controlled by a PC. Impedance measurements were performed in the frequency range from 50 kHz to 50 mHz, with ac voltage amplitude of 5 mV. Photocurrent was recorded during a linear potential sweep of 10 mV/s, using a chopped incident light from a 100 W tungsten halogen lamp. Summarizing, we can interpret the photocurrent and EIS results by taking into account that when the oxide layer is formed under potentiodynamic conditions, the Bi / Bi(III)oxide / electrolyte structure behaves like an n-type semiconductor and exhibits Mott-Schottky behavior. Also, when the oxide layer is formed under potentiostatic conditions, the passive electrode behaves as an insulator. In the fitting procedure of EIS spectra using a powerful complex nonlinear least squares fitting program, different equivalent circuits are discussed. A Maxwell-type five-element equivalent circuit (involving surface states) could be taken as a reasonable model for the impedance data combined with the results of Mott-Schottky measurements. We think the EEC model presented in this paper is excellent for quantitative analysis of the characteristics of the Bi-oxide/electrolyte interface.

Bismuth; valve metals; bismuth oxide; semiconductor; insulator; photopolarization; electrochemical impedance spectroscopy; potoelectrochemistry

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