2003 Volume 71 Issue 4 Pages 266-273
Electrogeneration of superoxide ion (O2−) via one-electron reduction of dioxygen (O2) in aqueous solution has been examined with various thiol-modified Au electrodes. Based on the reactions between O2− and superoxide dismutase (SOD) or ferric cytochrome c (cyt.c (Fe3+)), thiols (thiol compounds) such as n-hexadecanethiol, n-decanethiol, mercaptoacetic acid and 3-mercaptopropionic acid were found to be new electrode modifiers which allow the electrogeneration of O2− on Au electrode. The current efficiencies for the electrogeneration of O2− at these thiol-modified Au electrodes were ca. 4%. Some probable mechanisms for the electrogeneration of O2− at the modified electrodes are discussed. It is concluded that, unlike quinoline compounds adsorbed on Hg electrode which are known to form liquid-like hydrophobic layers favorable for the electrogeneration of O2−, the thiols adsorbing as self-assembled monolayers on the Au electrode surface do not necessarily form such hydrophobic layers, but prevent or reduce the spontaneous dismutation between O2 molecules adsorbing on the Au electrode surface by spatially separating them each other as a result of the adsorption of the thiol molecules themselves on it and consequently the electrogeneration of O2 can be realized at these thiol-modified Au electrodes.
