Study of the Electroless Deposition of Pd on Cu-Modified Graphite Electrodes by Metal Exchange Reaction

The electroless deposition of Pd on Cu-modified graphite electrodes using a metal exchange reaction was investigated. The modification procedure consisted in the electrodeposition of Cu on the graphite electrode, subsequently replaced by Pd at open circuit in a Pd-containing solution. The influence of experimental conditions on the exchange reaction rate, the chemical state and the distribution of Cu and Pd on the electrode surface are highlighted. The resulting deposits were studied using cyclic voltammetry, atomic absorption spectroscopy, scanning electron microscopy, energy-dispersive X-ray, and X-ray photoelectron spectroscopy. The last technique confirmed the spontaneous oxidation of Cu by the Pd complexes adsorbed on the electrode surface and also demonstrated that Pd/Cu atomic ratio increases by increasing the PdCl 2 concentration. An increase of the Pd electroactive surface area, estimated by cyclic voltammetry, was observed by increasing the initial Cu loading, the exchange reaction time or the PdCl 2 concentration. It was also demonstrated that the metal exchange reaction leads to the formation of a Cu core enveloped by a Pd shell for every PdCl 2 concentration investigated here. The corrosion rate for the corrosion of copper by a Pd complex was determined and compared with that of the corrosion of copper by oxygen. On the basis of our observations, a general model to describe the Cu−Pd exchange process and the resulting electrode surface composition was proposed.