Electrochemical characterization of oxygen reduction by Fe II[ethylenediaminetetraacetate]

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Vol. 608; no. 2; pp. 111 - 116
• Main Authors: Laine, Derek F., McAllister, Simon D., Cheng, I. Francis
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-10-2007
• Subjects: Autoxidation; Cyclic voltammetry; Digital simulation; Fe IIEDTA; Cyclic voltammetry; Autoxidation; Fe IIEDTA; Digital simulation
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2007.05.012

The kinetics of the reduction of O
2 by Fe
IIEDTA is evaluated using electrochemical methods and shows a promising approach to the study of oxygen activation by metal complexes. Beneficial to this method is the use of stable Fe
IIIEDTA, which can be electro-reduced to generate air sensitive Fe
IIEDTA. The Fe
II/IIIEDTA oxidation states act as an electron mediator between the electrode and O
2(aq). At a sweep rate of 5
mV/s, cyclic voltammeteric waves indicate an EC’ type mechanism. The kinetics of O
2 reduction by Fe
IIEDTA is evident by the EC’ current and is dependent on pH with a maximum at pH 3. This rate quickly decreases below pH 3 and above 8 and is nearly constant between pH 4–8. This behavior is strongly correlated with the Fe
IIEDTA species distribution diagram indicating that the protonated Fe
IIEDTA–H complex is the optimal species for O
2 reduction. Applying computer simulation to representative cyclic voltammograms provides rate constants for the reaction steps involved in O
2 reduction by Fe
IIEDTA. The mechanistic steps evaluated consist of (1) the binding of O
2 to Fe
IIEDTA, (2) the reduction of bound O
2 by Fe
IIEDTA to produce
O
2
-
, and (3) further reduction of
O
2
-
by Fe
IIEDTA to produce H
2O
2. We report a rate constant of 1.07
×
10
4
M
−1
s
−1 for step (1), 6.23
×
10
9
s
−1 for step (2), and 1.00
×
10
4
M
−1
s
−1 for step (3) at pH 3. The data is consistent to literature values obtained by stopped-flow techniques.