Catalysis of the electrochemical oxygen reduction in room-temperature ionic liquids on a pyrolytic graphite electrode by iron-containing superoxide dismutase |
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| Authors: | K. Ding M. Zhao Q. Wang |
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| Affiliation: | (1) Chemistry and Material Science College, Hebei Teacher’s University, Shijiazhuang, 050016, P.R. China;(2) Huihua College, Hebei Teacher’s University, Shijiazhuang, 050091, P.R. China;(3) Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8502, Japan |
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| Abstract: | Catalysis of the electrochemical oxygen reduction reaction (ORR) on a pyrolytic graphite electrode (PGE) by iron-containing superoxide dismutase (Fe-SOD) is investigated for the first time using cyclic voltammetry and electrochemical impedance spectroscopy. The study is carried out in three room-temperature ionic liquids (RTILs), namely, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), 1-propyl-3-methylimidazolium tetrafluoroborate (PMIBF4), and 1-butyl-3-methylimidazolium tetrafluoroborate (EMIBF4). The results demonstrate that in EMIBF4, Fe-SOD exhibits the most satisfactory catalysis for ORR, with the standard rate constant of ORR on bare PGE, k s, increasing from 3.9 to 5.1 times 10−3 cm s−1, while in PMIBF4 and BMIBF4 containing Fe-SOD k s increases from 2.6 to 3.6 and from 1.4 to 2.2 times 10−3 cm s−1, respectively. In addition to the increased k s, adding Fe-SOD renders the formal potential of ORR more positive. To accelerate the electron transfer, multi-walled carbon nanotubes (MWCNTs) are employed to modify PGE, consequently, yielding the dramatically increased peak current and k s. For MWCNTs-modified PGE in EMIBF4 free of Fe-SOD, k s increases from 3.9 to ∼7.1 times 10−3 cm s−1. The ORR catalysis by Fe-SOD in the presence of Fe-SOD is also evidenced by the formal-potential shift in the positive direction. With MWCNTs accounting for the larger k s and Fe-SOD being responsible for the formal-potential shift, the catalysis of ORR is satisfactory. Chronocoulmetry experiments proved that some Fe-SOD could be adsorbed on PGE. After analyzing the results, dismutation of superoxide anion O 2 − by Fe-SOD is thought to be the main reason for the formal-potential shift. The different polarity of RTILs is probably partly responsible for different k s obtained in different RTILs. Basing on an earlier proposition, the catalysis of ORR by MWCNTs in RTILs is discussed. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 9, pp. 1137–1146. The text was submitted by the authors in English. |
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| Keywords: | iron-containing superoxide dismutase room-temperature ionic liquids electrochemical oxygen reduction reaction multi-walled carbon nanotubes pyrolytic graphite electrode |
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