Simple preparation method of Pd nanoparticles on an Au electrode and its catalysis for dioxygen reduction

Abstract

A simple method for the fabrication of Pd nanoparticles is described. The three-dimensional Pd nanoparticle films are directly formed on a gold electrode surface by simple electrodeposition at −200 mV from a solution of 1 M H₂SO₄ + 0.01 mM K₂PdCl₄. X-Ray photoelectron spectroscopy verifies the constant composition of the Pd nanoparticle films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 45–60 nm. It is confirmed that the morphology of the Pd nanoparticle films are correlated with the electrodeposition time and the state of the Au substrate. The resulting Pd-nanoparticle-film-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen in 0.1 M KCl solution. Freshly prepared Pd nanoparticles can catalyze the reduction of O₂ by a 4-electron process at −200 mV in 0.1 M KCl, but this system is not very stable. The cathodic peaks corresponding to the reduction of O₂ gradually decrease with potential cycling and at last reach a steady state. Then two well-defined reduction peaks are observed at −390 and −600 mV vs. Ag/AgCl/KCl (sat.). Those two peaks correspond to a 2-step process for the 4-electron reduction pathway of O₂ in this neutral medium. The former peak is ascribable to the 2-electron reduction of O₂ to H₂O₂, while the latter is assigned to the reduction of H₂O₂ to H₂O. The observed electrocatalysis for the reduction of O₂ is attributable to the extraordinary catalytic activity of the Pd nanoparticles over the bulk gold electrode.