Full factorial design applied to the synthesis of Pd-Ag nanobars by the polyol method and the perspective for ethanol oxidation

Full factorial design methodology was applied to the synthesis and optimization of Pd-Ag nanobars using the polyol process as the reducer. The concentration of Br^- ions, the temperature and the reaction time were selected as factors to study, whereas the yield (% nanobars) was the response to be analyzed. The nanoparticles were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The nanoparticles were also tested for the ethanol electro-oxidation reaction by cyclic voltammetry in alkaline solution. The three factors had a positive effect on the response: the nanobar yield increased as the level of the variables changed from -1 to +1. The temperature and reaction time were the most determinant variables (main and interacting) on the nanobar yield, whereas the concentration of Br^- influenced the yield to a lesser extent. After designing three optimum experiments, a maximum nanobar yield of 47.3% was obtained. The more negative electro-oxidation onset, higher current density and more negative current peak potential show that the incorporation of Ag into Pd nanobars improves the kinetic and thermodynamic behavior towards the ethanol electro-oxidation reaction compared with that obtained with nanometrically pure Pd nanobars. This improvement is the result of surface modification caused by the incorporation of Ag in the formation of Pd-Ag bimetallic nanobars with (200) surfaces.