rXXXX American Chemical Society A dx.doi.org/10.1021/la202174j | Langmuir XXXX, XXX, 000–000 ARTICLE pubs.acs.org/Langmuir Selective Electrodesorption Based Atomic Layer Deposition (SEBALD): a Novel Electrochemical Route to Deposit Metal Clusters on Ag(111) M. Innocenti, S. Bellandi, E. Lastraioli, F. Loglio, and M. L. Foresti* Dipartimento di Chimica, Universit  a di Firenze, via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy ’ INTRODUCTION Today, electrochemistry extends to the domain of material science because of the development of electrochemical methods for the electrodeposition of materials controlled down to the atomic level. On silver, well-ordered atomic layers can be often obtained by exploiting surface phenomena such as underpoten- tial deposition (UPD). 1 Recently, interest in the underpotential electrodeposition of elements has increased essentially due to potential applications in several fields of technology such as photovoltaics and electro- catalysis. In photovoltaics, one example is the possibility of depositing alternate UPD layers of metals and nonmetals to grow binary and ternary compound semiconductors. This meth- odology is the basis of the electrochemical atomic layer epitaxy (ECALE) method proposed by Stickney and co-workers 2 and extensively used to grow cadmium sulfide on gold. 3À9 The ECALE method was adopted in our group to grow cadmium and zinc chalcogenides on silver single crystals, with particular attention to binary and ternary sulfides. 10À13 In fact, unlike Se and Te that require more complex procedures to yield UPD layers, S UPD is simply obtained by oxidative underpotential deposition from sulfide ion solutions. In electrocatalysis, there is growing interest in the development of new substrates for cathodic reactions for employment both in the electrolysis of water and in oxygen reduction reaction (ORR) for alkaline fuel cells. With the aim of completely removing Pt and replacing it with less expensive materials, guidelines for the design of bimetallic electrocatalysts for ORR have been proposed assuming a simple mechanism where one metal breaks the oxygenÀoxygen bond of molecular O 2 and the other metal acts to reduce the resulting adsorbed atomic oxygen. 14,15 More precisely, metals such as Co, Ni, or Fe should favor the initial dissociative chemisorption of oxygen, whereas silver should promote the following charge transfer steps. The theoretical predictions have been supported by the experimental evidence of catalytic activity of the AgÀCo mixtures. 14 More recently, we described the catalytic effect of Co monolayer islands formed on Ag substrate toward ORR. 16 As stated before, well-ordered layers of some metals can be deposited on silver at underpotential. Unfortunately, Co is not included between these metals, and therefore, the problem of limiting its deposition is crucial even working at very low overpotentials. To limit Co deposition to a monolayer, we exploited the surface limited redox replacement (SLRR) method. 17,18 According to this method, a layer of a metal deposited at underpotential is used as a template for the spontaneous deposition of a more noble metal mono- layer. In our case, the deposition of Co through SLRR method has been performed replacing a layer of Zn deposited at under- potential on silver. 16 Likewise, neither Ni nor Fe can be deposited at underpotential and require indirect methods. This paper presents a novel electrochemical route to deposit metal clusters on Ag(111). We called this method “selective electrodesorption based atomic layer deposition” (SEBALD). For its validation, the method was applied to obtain Cd layers from CdS that was a compound extensively studied in our group before. 10À13 Then, the first results for other metals like Co, Ni, and Fe are reported. ’ EXPERIMENTAL SECTION Fluka analytical reagent grade Na 2 S, and Merck analytical reagent grade CoSO 4 3 7H 2 O, 3CdSO 4 3 H 2 O, NiCl 2 , FeSO 4 3 7H 2 O, HClO 4 , Received: June 10, 2011 Revised: August 8, 2011 ABSTRACT: The possibility of synergic effects of some metals on the catalytic activity of silver led us to study the way to perform controlled deposition on silver. In fact, many metals of technolog- ical interest such as Co, Ni, and Fe cannot be deposited at underpotential on silver, and any attempt to control the deposition at overpotential, even at potentials slightly negative of the Nernst value, did not allow an effective control. However, due to the favorable energy gain involved in the formation of the correspond- ing sulfides, these metals can be deposited at underpotential on sulfur covered silver. The deposition is surface limited and the successive electrodesorption of sulfur leaves confined clusters of metals. The method can also be used to obtain metal clusters of different size. In fact, the alternate underpotential deposition of elements that form a compound is the basis of the electrochemical atomic layer epitaxy (ECALE), and the reiteration of the basic cycle allows us to obtain sulfide deposits whose thickness increases with the number of cycles. Therefore, the successive selective desorption of sulfur leaves increasing amounts of metals.