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Surface area measurements before and after de-alloying of Au x Ag (1-x) alloysFigure 1S represents the CV curves of Pb UPD on as deposited and de-alloyed Au 45 Ag 55 bulk polycrystalline alloys. It is clear that the charge is practically the same before and after a de-alloying potential conditions were applied to the sample and that clearly points toward a steady surface area.

Gold is epitaxially grown by spontaneous deposition (SD) on Pt(111) and Pt [poly]. It has been demonstrated that in the system of interest the SD takes place as a hybrid process, consisting of the potential-controlled reduction of an adsorbed [AuCl 4 ] − complex along with an electroless reduction of the same complex coupled with Pt surface oxidation over the course of adsorption. This hybrid deposition process is shown to promote an outstanding layer-by-layer growth mode on Pt(111) that involves the formation of smooth films with virtually no surface roughness increase. This finding is seconded by in-situ STM experiments demonstrating that the SD of Au on Au(111) leads to similar growth results. In addition, an adlattice structure of √ 7 × √ 7 r19.1 • is determined for the [AuCl 4 ] − adsorbate on Au (111) suggesting a theoretical deposited amount of about 15% Au surface coverage per SD cycle. It has been shown that a Pt(111) substrate is completely masked after five cycles of SD followed by layer densification in continuity development. It has also been shown that the Au amount deposited specifically through the electroless route can be controlled by the amount of initial Pt oxidation, the concentration of dissolved O 2 , and the duration of [AuCl 4 The deposition of thin noble metal films is an area of significant interest for the fundamental and applied communities alike. Noble metal monolayer, to multilayer structures on a sacrificial substrate allows for the utilization of the beneficial properties of electropositive metals or alloys such as; corrosion resistance and catalytic activity, while minimizing the metals use, thus promoting cost effectiveness. In addition it has been shown that monolayer to bilayer metal films on foreign substrates exhibit different electronic properties and chemisorption trends when compared to the bulk material. This is explained through the alteration of the d-band center and orbital mixing resulting from epitaxial strain and electron ligand effects.1-4 Overall, these unique properties can ultimately enhance a material's catalytic usefulness. 5,6 In addition to this it has also been shown that if a metal substrate is decorated by a sub-monolayer of a foreign metal in a controllable way, a synergism can result between the substrate and the foreign metal. This synergy results in enhanced properties, that in some cases are accompanied by the stabilization of the underlying substrate. [7][8][9][10][11] Adzic et al. have demonstrated that the electrodepostion of 0.26 to 0.33 layers of Au on an underlying Pt substrate not only results in steady oxygen reduction reaction activity but also, after 30,000 cycles, the accordingly decorated catalyst is proven significantly more durable than the Pt catalyst on its own.10 Hazzazi et al. have also shown that Au deposited via forced deposition on Pt with coverages up to 0.73 layers improve a catalysts activity toward the ethanol oxidation reaction. 12The above listed sample of advantages of ultrathin epitaxial and continuous noble metal f...

The development of durable fuel cell catalysts with high activity and low Pt loading is of paramount importance for the fuel cell’s industrial applicability. Conventionally Pt and Pt group metals have been shown to have the highest catalytic activity, however their durability has remained a concern due to CO poisoning and Pt dissolution [1, 2]. This has thusly necessitated the need for mixed metal catalysts, with improved durability, and conserved, or higher activity when compared to bulk Pt. It has been shown that the decoration of catalytically active metals with sub-monolayers of foreign metals can improve catalysts’ durability as well as its activity due to synergistic effects [3-7]. In addition it has been demonstrated that the creation of continuous ultrathin noble metal films on foreign substrates exhibit enhanced electronic and chemisorption properties when compared to the bulk material. This is explained through d-band theory and orbital mixing demonstrated by Norskov et al. [ 8-10 ] . These enhancements have created the need for simple low cost fabrication techniques of these materials, such as spontaneous deposition. Conventional spontaneous deposition involves the adsorption of an ordered ad-layer of a metal complex on a substrate. This adsorption is strong enough to withstand rinsing of the crystal, and then reduction in a solution of the supporting electrolyte. The limited amount of adsorbed complex results in excellent control of the amount of deposited metal, and the spontaneous deposition sequence can then be cycled multiple times in order to generate deposits of desired thicknesses. The spontaneous deposition of Au was previously discovered by this group when demonstrating the surface limited redox replacement of Au on Pt [11], and in this report it will be fundamentally demonstrated. Electrochemically, it will be shown that the spontaneous deposition of Au on Pt operates via a hybrid deposition mode, one that consists of conventional spontaneous deposition as well as an electroless step involving Pt oxidation and [AuCl4]- complex reduction. In addition, via STM, the ordered ad-layer of the [AuCl4]-  complex will be demonstrated and it will be shown that deposits generated via spontaneous deposition proceed via a nearly perfect 2-D layer by layer growth mode on both Pt and Au. Finally, it will be shown that the spontaneous deposition of Au on Pt is a suitable strategy for the decoration of Pt with sub-monolayer to nearly perfect multilayer Au films. References [1] A.B. Ofstad, M.S. Thomassen, J.L. Gomez de la Fuente, F. Seland, S. Mo̸ller-Holst, S. Sunde, Journal of The Electrochemical Society, 157 (2010) B621. [2] M. Fayette, J. Nutariya, N. Vasiljevic, N. Dimitrov, ACS Catal., 3 (2013) 1709-1718. [3] L.C. Grabow, Q. Yuan, H.A. Doan, S.R. Brankovic, Surface Science, 640 (2015) 50-58. [4] J.X. Wang, S.R. Brankovic, Y. Zhu, J.C. Hanson, R.R. Adzic, Journal of The Electrochemical Society, 150 (2003) A1108-A1117. [5] D. Wang, H.L. Xin, Y. Yu, H. Wang, E. Rus, D.A. Muller, H.D. Abruna, J. Am. Chem. Soc., 132 (2010) 17664-17666. [6] S.H. Bonilla, C.F. Zinola, J. Rodriguez, V. Diaz, M. Ohanian, S. Martinez, B.F. Gianetti, Journal of Colloid and Interface Science, 288 (2005) 377-386. [7] O.A. Hazzazi, G.A. Attard, P.B. Wells, F.J. Vidal-Iglesias, M. Casadesus, Journal of Electroanalytical Chemistry, 625 (2009) 123-130. [8] T. Bligaard, J.K. Norskov, Electrochimica Acta, 52 (2007) 5512-5516. [9] J. Greeley, J.K. Norskov, M. Mavrikakis, Annu. Rev. Phys. Chem., 53 (2002) 319-348. [10] B. Hammer, J.K. Norskov, Advances in Catalysis, 45 (2000) 71-129. [11] C. Mitchell, M. Fayette, N. Dimitrov, Electrochimica Acta, 85 (2012) 450-458.

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