Functionalization of Underpotentially Deposited Metal Layers with Organics, Metals, and Ions

Abstract

Underpotential deposition (upd) provides a convenient method for plating an atomic layer of one metal onto the surface of another more noble metal.¹ Examples include the underpotential deposition of metals such as copper and silver onto the more noble surfaces of gold and platinum.^{1, 2} The structure and composition of these and other adlayers—and their dependence on factors such as electrochemical potential, crystal structure of the electrode metal, and ions in the electrolyte—have been the topic of numerous investigations.^1–5 In constrast, little work has been directed toward modifying the upd surfaces with other agents, most likely due to a perception of extreme fragility for upd adlayers. We find that some upd systems—notably, upd adlayers of silver and of copper on gold—offer sufficient stability under conditions where they can undergo chemical and/or electrochemical modification.^6–14 Figure 1 schematically illustrates these processes of modification that are the topic of this chapter. Specifically, the upd layers can be derivatized by the adsorption of ligating species—examples include alkanethiols,^6–9 alkylphosphonic acids,¹⁰ and halides^12–14—and remain as a stable adlayer on the gold surface during this process. Notably, the presence of the monoatomic copper and silver adlayers alter the chemisorptive properties of the gold surface, thereby providing new approaches for modification. In addition, for some metal combinations, the upd adlayer can be modified electrochemically by the upd of a second metal onto the parent electrode surface to produce a two-component adlayer of monoatomic thickness on an electrode surface.¹¹