Electrochemical Design of Pt-Pd Nanostructures By Surface Limited Redox Replacement Method

Abstract

The fuel cell technology is a green alternative to fossil fuels [1-2]. Fuel cells are electrochemical systems that use hydrogen and oxygen to create electrical energy with water and heat as biproducts. Besides the main interest of fuel cells applications in the automotive industry, most recent developments of miniature fuel cells that use biomass derived hydrogen have been attracting attention. Such systems require the design of new electrocatalysts with the high CO tolerance better than that of pure Pt. It has been shown that nanoscale Pt such as ultrathin layers and Pt-M nano-alloys, often have improved chemical and physical properties than those of Pt-bulk material due to the combination of electronic and geometric effects. Previous studies have reported that Pt-Pd system is a well-performing catalytic system for future use with the high CO tolerance [3,4]. Surface Limited Redox Replacement (SLRR) is one of the most successful approaches used to produce Pt bimetallic catalysts with high control of atomic structure [5, 6]. This method is based on the replacement of an underpotentially deposited (UPD) layer of a less noble metal by a more noble (such as Pt and Pd) through irreversible surface-controlled redox reaction. Here we will present SLRR based design of Pt-Pd nanoalloys of different composition on Au substrate. The advantages of using the SLRR method to design high quality 2D model Pt alloys will be demonstrated by studies of their electrochemical and catalytic behaviour as a function of structure such as film thickness and alloy composition. In our work, the epitaxial alloy thin films up to 10 ML thickness were grown in one-cell configuration using Cu UPD in sulphate solution as sacrificial layer. The alloys composition and structure were controlled by the concentration ratio of Pt and Pd complex in the solution. The structure of developed alloys was examined by a combination of electrochemical and surface science methods and correlated with their electrocatalytic behaviour during formic acid oxidation reaction.