Fabrication of Au(111)-Like Polycrystalline Gold Electrodes and Their Applications to Oxygen Reduction

Abstract

In the present study, we introduced a simple method for the fabrication of Au͑111͒-like polycrystalline Au electrodes via the formation of a submonolayer ͓i.e., sub-self-assembled monolayer ͑sub-SAM͒/Au͔ of a thiol compound ͓e.g., cysteine ͑CYST͒, mercaptoacetic acid, or cystamine͔. The oxygen reduction reaction ͑ORR͒ in alkaline medium (O 2 -saturated 0.5 M KOH͒ 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 (⌬E p ) of about 60 mV͔. This behavior is similar to that observed at the Au͑111͒ 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 Au͑111͒ 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 ϩ200 and Ϫ500 mV at a scan rate of 50 mV s Ϫ1 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 Ϫ ions ͓which possess a strong adsorption tendency toward Au͔ cannot replace the CYST molecules.

Microstructures by Selective Desorption of Self‐Assembled Monolayer from Polycrystalline Gold Electrodes

“…Recently Ohsaka et al [16,19,20] analyzed the reductive desorption behavior of cysteine, 4-mercaptobenzoic acid and mercaptoacetic acid from poly-Au electrodes by comparing the position of the desorption peaks to the peak position for desorption from single crystalline gold substrates. The multiple waves observed at poly-Au were correlated with the single reductive desorption waves of the low index surfaces, i.e., (111), (100) and (110) of the single crystalline gold substrates [16,19]. The stability of the adsorbates differs substantially depending on the surface crystallographic orientation, in the order (111) < (100) < (110).…”

“…This is an exception, since reductive desorption from single crystal surfaces normally proceed in a single reduction step, resulting in a single desorption peak. A single peak is also observed for the desorption of MPA from each of the single crystal planes Au(111) [14,16,19], Au(110) and Au(100) [16,19]. It is not very likely that the change from a single crystalline gold substrates to poly-Au could would lead to a change in the fundamental reduction mechanism, though it can not totally ruled out.…”

Electrochemical Performance of Self‐Assembled Monolayer Gold Nanoparticle‐Modified Ultramicroelectrode Array Architectures

“…Selective desorption of the SAMs was achieved in order to improve the performance/control of the porosity of the thiolated layer that guarantees a partially unblocked electrode surface with a high number of bare exposed domains on the electrode surface [25]. Reductive partial desorption of MUA SAM from the microelectrode surface was carried out by LSV (Figure 3, Inset).…”

“…A similar behavior was observed for other SAMs formed by short-chain thiolated molecules. For instance, it was previously reported that O 2 reduction was completely blocked at an intact threecarbon cysteine SAM-coated gold electrode [25]. However, this reaction was possible when cysteine was selectively desorbed from the electrode surface and a SAM submonolayer was thus obtained.…”

“…Accordingly, tailoring defective SAMs for the development of amperometric biosensors is quite appealing, since a stable tethering of the biological receptor could be achieved without compromising the electron transfer process at a gold electrode surface. Indeed, the formation of SAMs on gold electrodes and the effect of their selective desorption have been broadly studied [14,[25][26][27][28][29][30][31][32].…”