Low cost Pd–W nanoalloy electrocatalysts for oxygen reduction reaction in fuel cells

Abstract

Carbon supported Pd_{100 − x}W_x (0 ≤ x ≤ 30) nanoalloy electrocatalysts have been synthesized by simultaneous thermal decomposition of palladium acetylacetonate and tungsten carbonyl in o-xylene in the presence of Vulcan XC-72R carbon, followed by annealing up to 800 °C in H₂ atmosphere. Characterization of the Pd–W samples by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) energy dispersive spectroscopic (EDS) analysis in scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicates the formation of single phase face centered cubic (fcc) solid solutions for 0 ≤ x ≤ 20 with controlled composition and morphology. The TEM data indicate an increase in particle size with increasing heat treatment temperature. Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements reveal that the alloying of Pd with W enhances the catalytic activity for the oxygen reduction reaction (ORR) as well as the stability (durability) of the electrocatalyst compared to the unalloyed Pd. The composition Pd₉₅W₅ exhibits the maximum activity for ORR in the Pd–W system. The Pd–W catalysts show high tolerance to methanol electro-oxidation compared to a Pt catalyst, which may offer important advantages in employing the Pd-based electrocatalysts for ORR in direct methanol fuel cells.