Synthesis of Pd Fe3O4 nanoparticles varying the stabilizing agent and additive and their effect on the ethanol electro-oxidation in alkaline media

Abstract In this work, Pd Fe 3 O 4 nanoparticles were synthesized by varying the stabilizer (hexadecyltrimethylammonium bromide ‘CTAB’ and betaine) and using NaBr as additive. X-ray diffraction (XRD) patterns of Pd Fe 3 O 4 nanoparticles synthesized using betaine or CTAB displayed similar intensities and positions of Bragg's angles, resulting in a low contribution of the surfactant in the crystallite size and lattice parameter. The iron content increased in CTAB systems as was determined by X-ray fluorescence (XRF), finding the highest content (Pd 85 Fe 15 ) with the combination of CTAB and NaBr. X-ray photoelectron spectroscopy (XPS) indicated that the iron species on the surface are due to the presence of Fe 3 O 4 . High-resolution TEM images and XRD revealed that NaBr promoted the decrease of crystallinity and particle size of Pd Fe 3 O 4 , diminishing it from 6.5 and 6.2 nm to 4.4 and 2.7 nm in the betaine and CTAB systems, respectively. The decrease of the particle size of Pd Fe 3 O 4 obtained combining CTAB + NaBr improved the electrochemically active surface area, enabling the highest activity in comparison with the other Pd Fe 3 O 4 materials. In addition, this Pd Fe 3 O 4 (CTAB + NaBr) material displayed higher current densities and lower oxidation peak potentials than a Pd/C (CTAB + NaBr) material, which was used as reference. Therefore, the activity of Pd Fe 3 O 4 was also related to the presence of iron oxide, which decreased the energy barriers for ethanol oxidation due to an improvement of the electronic properties by a close vicinity between Pd and Fe atoms, modifying the crystallinity, lattice parameters, interatomic distances and binding energies.