Synthesis and Characterization of Nanostructured Pd−Mo Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells

Carbon-supported Pd100-xMox (0 ≤ x ≤ 40) nanoparticles have been synthesized by a simultaneous thermal decomposition of palladium acetylacetonate and molybdenum carbonyl in an organic solvent (o-xylene) in the presence of Vulcan XC-72R carbon, followed by heat treatment up to 900 °C in H2 atmosphere and characterized chemically and structurally. X-ray diffraction data reveal the formation of single-phase face-centered cubic solid solutions for 0 ≤ x ≤ 30 after heat treating at 900 °C and the occurrence of a Mo2C impurity phase for x = 40. The particle size of the Pd100-xMox samples increase with increasing heat treatment temperature as revealed by transmission electron microscopy. Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements reveal that the alloying of Pd with Mo enhances the catalytic activity for the oxygen reduction reaction (ORR) as well as the stability (durability) of the electrocatalyst. However, the activity reaches a maximum at Pd90Mo10 and then decreases with increasing Mo content. Similar observations are made in both single-cell proton-exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) for the ORR activity. Interestingly, the 900 °C Pd90Mo10 exhibits catalytic activity for ORR in DMFC at 80 °C similar to that of as-synthesized Pt despite a significantly larger particle size due to a high tolerance of Pd90Mo10 to methanol poisoning.