Reaction Kinetics of Metal Deposition by Surface Limited Redox Replacement of Upd Monolayer
Noble metal coatings have been used in many applications such as catalysts, corrosion protection, and microelectromechanical systems (MEMs). Using the monolayer coating concept lowers the ultimate cost by reducing noble metal content. Underpotential deposition (UPD) and Surface Limited Redox Replacement (SLRR) reactions are two significant monolayer deposition methods that have gained more attention lately in catalyst design community. To have a more precise deposition and control of monolayer catalysts morphology, it is important to know more about reaction kinetics, such as reaction rate constant and half time of the reaction. By varying the coverage of UPD layer using deposition via SLRR, it is possible to control the amount of monolayer deposit accurately down to a fraction of monolayer. Since in SLRR, galvanic displacement of UPD monolayer occurs at open circuit potential (OCP), conventional charge measurement method is not capable of monitoring deposited amount of noble metal. In addition, the OCP model equations derived from Bruckenstein-Swathirajan (BS) isotherm and rate equations have four or more fitting parameters which causes complexity of the fits and interpretation of the results. The objective of this research is to study reaction kinetics of Au deposition by surface-limited redox replacement (SLRR) of lead underpotential deposited (UPD) mono layer (ML) on Au (111) single crystal by surface reflectivity measurements. This approach involves fitting procedures that has only one adjustable parameter. Our system is proved to be successful in measuring reaction rate constants by fitting rate equation to the Pb UPD coverage transients during SLRR. Thus, this system is used to do reaction kinetics analysis in Au deposition via SLRR of Pb UPD ML.