Electrochimica Acta 56 (2011) 8291–8298 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Au dissolution during the anodic response of short-chain alkylthiols with polycrystalline Au electrodes Scott. R. Smith a , Eduard Guerra b , Stefan Siemann a , Jeffrey L. Shepherd a,∗ a Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario P3E 2C6, Canada b School of Engineering, Laurentian University, Sudbury, Ontario P3E 2C6, Canada a r t i c l e i n f o Article history: Received 12 May 2011 Received in revised form 28 June 2011 Accepted 28 June 2011 Available online 6 July 2011 Keywords: 3-Mercaptopropionic acid Meso-2,3-dimercaptosuccinic acid Oxidative desorption Au dissolution Electrochemical impedance spectroscopy a b s t r a c t The electrochemical characteristics of polycrystalline Au in LiClO 4 electrolyte solutions containing 3- mercaptopropionic acid (MPA) or meso-2,3-dimercaptosuccinic acid (DMSA) were studied with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) over a wide range of pos- itive potentials vs. Ag/AgCl. The EIS data exhibited linear capacitive behaviour at 0.0 V with either MPA or DMSA added directly to the electrolyte suggesting the formation of an adsorbed layer of the alkylthiol on the electrode surface. Above this potential, a single well-defined impedance loop appeared for elec- trolyte solutions containing DMSA or MPA, an observation indicative of a charge transfer reaction that could be related to several processes including oxidative desorption, oxidation of the alkylthiol, or Au oxidation/dissolution. To test for Au dissolution, the electrode was held at 0.8 V vs. Ag/AgCl for 12 h in elec- trolytes containing MPA or DMSA followed by surface analysis with Atomic Force Microscopy and solution analysis with Atomic Absorption Spectroscopy. When the electrolyte contained MPA, the extended poten- tial holding procedure resulted in significant roughening of the electrode with no detectable quantities of Au in the electrolyte. X-ray photoelectron spectroscopy (XPS) analysis of the Au surface revealed an additional species in the Au 4f 7/2 spectrum indicating the presence of an insoluble electrochemically gen- erated Au(I)–MPA species. When the electrolyte contained DMSA, the Au electrode appeared smoother, 56.6 ± 9.6 ppb of Au was detected in the electrolyte and the XPS analysis displayed a single species in the Au 4f 7/2 spectrum indicative of metallic Au after the potential holding procedure. Both observations with MPA and DMSA support the charge transfer resistance to be at least partially related to the corrosion of Au, but also suggest that an electrochemically generated Au–DMSA species is soluble and of potential industrial relevance. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Over the past couple decades, alkylthiols have been intensely studied because of their ability to form compact self-assembled monolayers (SAMs) on noble metals, most notably Au [1]. Their properties when adsorbed on Au surfaces have been the focus of numerous investigations which include those related to corrosion resistance, lubrication, and also the development of biochem- ical/chemical sensors [2,3]. Because of their broad use, the properties and stability of alkylthiol SAMs on Au have been extensively studied and reviewed [4]. From an electrochemical per- spective, it is well known that alkylthiol SAMs behave differently over a wide range of electrode polarizations. Near the potential of ∗ Corresponding author. Tel.: +1 705 675 1151x4387; fax: +1 705 675 4844. E-mail address: jshepherd@laurentian.ca (J.L. Shepherd). zero charge (pzc) SAMs are stable but will undergo desorption at significantly negative or positive potentials. Reductive desorption of a thiol SAM in a basic electrolyte has been one of the most common electrochemical methods to char- acterize and manipulate alkylthiols on Au and the mechanism is relatively well described [5–8]. In contrast, the oxidative response of alkylthiol SAMs has remained unclear as the electrochemical peaks are convoluted and too large to be considered to originate from a simple one-electron process [9]. Because of this, several mechanisms have been identified. In the earliest reports, a three electron mechanism for oxidative desorption was proposed as described by Eq. (1) [5]: AuSR + 2H 2 O → Au(0) + RSO 2 H + 3e - + 3H + (1) Others have identified different desorbed species produced by the oxidative process including; acids, and/or sulphinates [10]. The mechanism for the oxidative response of alkylthiols has been fur- ther studied [11] and found to be dependent on the electrolyte 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.06.092