Effect of oxygen vacancies in anodic titanium oxide films on the kinetics of the oxygen electrode reaction |
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Authors: | B Roh D D Macdonald |
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Institution: | (1) Pennsylvania State University, University Park, PA 16802, USA |
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Abstract: | The effect of oxygen vacancies in the anodic oxide film on passive titanium on the kinetics of the oxygen electrode reaction
has been studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Oxide films of different
donor density were prepared galvanostatically at various current densities until a potential of 20.0 VSHE was achieved. The semiconductive properties of the oxide films were characterized using EIS and Mott-Schottky analysis, and
the thickness was measured using ellipsometry. The film thickness was found to be almost constant at ∼44.7 ± 2.0 nm, but Mott-Schottky
analysis of the measured high frequency interracial capacitance showed that the donor (oxygen vacancy) density in the n-type passive film decreased sharply with increasing oxide film formation rate (current density). Passive titanium surfaces
covering a wide range of donor density were used as substrates for ascertaining relationships between the rates of oxygen
reduction/evolution and the donor density. These studies show that the rates of both reactions are higher for passive films
having higher donor densities. Possible explanations include enhancement of the conductivity of the film due to the vacancies
facilitating charge transfer and the surface oxygen vacancies acting as catalytic sites for the reactions. The possible involvement
of surface oxygen vacancies in the oxygen electrode reaction was explored by determining the kinetic order of the OER with
respect to the donor concentration. The kinetic orders were found to be greater than zero, indicating that oxygen vacancies
are involved as electrocatalytic reaction centers in both the oxygen evolution and reduction reactions.
This paper was submitted in honor of the many contributions to electrochemistry that have been made by Professor Boris Grafov.
The article is published in the original. |
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Keywords: | titanium defect structure oxygen electrode reaction |
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