Kinetics of oxygen reduction reaction on nanosized Pd electrocatalyst in acid media

Palladium electrocatalyst powder was prepared through PdCl2 reduction with NaBH4 in a THF solution at 0 degrees C. Characterization of the palladium phases, morphology and topography was performed by XRD, SEM, and AFM. Results from the X-ray diffraction (XRD) study showed evidence of nanocrystalline fcc hexagonal palladium formation with 4 nm in an average size. Electrocatalyst activity for the oxygen reduction reaction, ORR, was examined using cyclic voltammetry through rotating-disk electrode measurements in a 0.5 M H2SO4 electrolyte. Kinetic results suggest that the initial electron transfer is the rate-determining step. An apparent enthalpy of activation Delta H degrees(#) = 89.5 +/- 0.5 kJ mol(-1) was calculated from electrochemical results at different temperatures. Based on current densities and the enthalpy of activation results, the nanosized Pd catalysts are significantly less active for the ORR than Pt and Ru electrocatalysts. (C) 2007 Elsevier B.V. All rights reserved.