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

Abstract

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.