The Spontaneous Deposition of Au on Pt (111) and Polycrystalline Pt

Abstract

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.