The influence of Cu adatoms on the Zn upd on polycrystalline thin gold film electrodes: a study using surface conductance measurements M.H. Fonticelli, D. Posadas, R.I. Tucceri * Departamento de Qu  ımica, Facultad de Ciencias Exactas, Instituto de Investigaciones Fisicoqu  ımicas Te oricas y Aplicadas, Universidad Nacional de La Plata, Sucursal 4, Casilla de Correo 16, 1900 La Plata, Argentina Received 31 October 2003; accepted 7 November 2003 Abstract The adsorption behaviour of Zn upd and irreversibly adsorbed Cu on thin gold films in a NaH 2 PO 4 electrolyte was studied applying both CV and surface conductance (SC) measurements. These processes were studied separately and the upd of Zn in the presence of previously adsorbed Cu was also studied. Zn upd and ups occur with an apparent number of transferred electrons n ¼ 1. The SC measurements show that Zn upd does not conform the surface Linde rule. The n value obtained can be explained by considering that the product is not Zn(0). The SC response of Cu irreversibly adsorbed on gold shows an increase in SC as the degree of coverage increases. The voltammetric response for the upd of Zn on Cu-covered gold electrodes shows that a Cu coverage around h Cu  0:66 is enough to inhibit the Zn upd process on gold completely. The charge relation (Q Cu vs. Q Zn ) shows that one Cu adatom blocks one Zn site. The SC shows that the response of Zn on Cu pre-adsorbed on gold is additive. This last behaviour can be explained only by inferring a phase segregation in two dimensions where Cu and Zn depositions occur in the form of individual islands. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Zn upd on gold; Cu irreversibly adsorbed on gold; Zn upd on Cu-coated gold electrodes; Surface resistance 1. Introduction Most upd studies deal with the deposition of a single metal-ion on a definite substrate. However, upd of two or more metal ions has received little attention. Schmidt and Gygax [1], studying upd in binary systems, con- cluded that partial coverage with a metal having a more positive peak potential leads to a blocking of surface sites for the deposition of a second metal with a more negative peak potential. Stucki [2] studied various co- upds of Tl þ , Cu þ2 , Pb þ2 and Ag þ on Au. Pauling and J€ uttner [3] studied sequential upd of Tl þ and Ag þ on Au(1 1 1). Co-upd of silver and bismuth on polycrys- talline and single-crystal gold electrode surfaces has been reported by Schroter and Solomun [4]. Simulta- neous deposition of lead and thallium on polycrystalline silver electrode surfaces has also been studied [5,6]. On Pt(1 1 1), Al-Akl and Attard investigated the upd of copper onto Pd/Pt(1 1 1) bimetallic electrodes [7] while El-Maksoud et al. reported the co-upd of copper and zinc [8] and Dollar et al. studied the co-irreversible de- position of bismuth and arsenic [9]. Smith and Abru~ na studied the upd of copper onto irreversible adsorbed bismuth-modified Pt(1 1 1) and Pt(1 0 0) [10]. Other types of composite surfaces, depending on the strength of the specific interaction between the adsorbates and the me- tal substrate, were reported [10]. The co-adsorption processes can potentially modify the catalytic activity over the respective homogeneously modified electrode surface in a manner analogous to the bulk alloying of two or more metals. The advantage of this approach is that the deposition process and surface Journal of Electroanalytical Chemistry 565 (2004) 359–366 www.elsevier.com/locate/jelechem Journal of Electroanalytical Chemistry * Corresponding author. Tel.: +0054-221-425-7291/425-7430; fax: +0054-221-425-4642. E-mail address: rtucce@inifta.unlp.edu.ar (R.I. Tucceri). 0022-0728/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2003.11.003