Shape-controlled palladium nanowires and nanoparticles electrodeposited on carbon electrodes

Abstract

Palladium nanoparticles and nanowires were electrodeposited on two carbon electrode surfaces, highly oriented pyrolytic graphite and glassy carbon, and extensively characterised by voltammetry and atomic force microscopy (AFM). The electrochemical behaviour in buffer solution of the palladium nanostructures, electrodeposited at different potentials from two concentrations of palladium (II) sulphate, was investigated. The electrodeposition parameters, the concentration of the precursor solution and the topography of the carbon substrate influenced the morphology, size, shape and distribution of the palladium nanostructures electrodeposited, which can enable attractive applications in nanotechnology. The dimensions of nanoparticles and nanowires of palladium electrodeposited on the surface of carbon electrodes using overpotential deposition (OPD) or underpotential deposition (UPD) conditions were determined by AFM. Continuous and homogeneous nanowires were formed by UPD at low concentrations of palladium ions and small uniformly distributed spherical nanoparticles were formed by OPD for higher concentrations of palladium ions. The formation of a palladium oxide pre-monolayer film begins at a negative potential and is strongly dependent on the size and morphological characteristics of the Pd(0) nanostructures existent on the surface of the electrode, relevant for palladium electrocatalysis. At high positive potentials, the Pd(0) on the electrode surface undergoes oxidation leading to the formation of a mixed oxide layer that may also operate as nucleation points for additional Pd metal growth, increasing the metal electrode surface coverage.