Fabrication of Au(111)-like polycrystalline gold electrodes and their applications to oxygen reduction

In the present study, we introduced a simple method for the fabrication of Au(111)-like polycrystalline Au electrodes via the formation of a submonolayer [i.e., sub-self-assembled monolayer (sub-SAM)/Au] of a thiol compound [e.g., cysteine (CYST), mercaptoacetic acid, or cystamine]. The oxygen reduction reaction (ORR) in alkaline medium (O-2-saturated 0.5 M KOH) performed at these sub-SAM/Au electrodes proceeds via a two-electron quasi-reversible pathway irrespective of the charge of the terminal group of the thiol [with anodic-to-cathodic peak separation (DeltaE(p)) of about 60 mV]. This behavior is similar to that observed at the Au(111) single-crystalline electrode in the same medium. The presence of iodide ions in the alkaline medium leads to a significant negative shift of the reduction peak while the anodic peak is completely ceased. This indicates the blocking of the Au(111) domain of the sub-SAM/Au by the iodide ions, leading to the complete inhibition of the anodic oxidation of the hydrogen peroxide formed during the cathodic scan. At the CYST sub-SAM/Au electrodes, the O-2 reduction is completely hindered in O-2-saturated 0.1 M KI, while the quasi-reversible behavior of the sub-SAM/Au electrode toward the ORR is restored after ten successive potential cycles between +200 and -500 mV at a scan rate of 50 mV s(-1) in O-2-saturated 0.5 M KOH. This indicates the high stability of the submonolayer of CYST at the Au electrode and that the I- ions [which possess a strong adsorption tendency toward Au] cannot replace the CYST molecules. (C) 2004 The Electrochemical Society.