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Abstract

ORR (Oxygen Reduction Reaction) has been studied on Pt-Pd/C catalyst both experimentally and theoretically to gain insight into the promotion effect of PtPd nanoclusters to ORR and to provide guidelines for the design of an improved ORR catalyst. First, Pt₃Pd₁/C, Pt₁Pd₁/C, and Pt/C catalysts were prepared by the polyol process in ethylene glycol solution and characterized by XRD (X-ray diffraction), TEM (transmission electron microscope), and CV (cyclic voltammetry) techniques. XRD patterns reveal that all the catalysts have disordered face-centered cubic structures similar to the commercial Pt/C catalyst. Low-resolution TEM images indicate that the dispersion of the metal nanoparticles on the carbon support is uniform and in a narrow particle size range for Pt₃Pd₁/C and Pt/C catalysts, while for Pt₁Pd₁/C catalyst, the dispersion of the metal nanoparticles on the carbon support is uneven with a little agglomeration. Point resolved EDS (energy dispersive X-ray spectroscopy) of the individual particles have shown that both Pt and Pd are represented in the single nanoparticle for the Pt-Pd/C catalysts. CV tests show that Pd-containing catalysts of Pt₃Pd₁/C and Pt₁Pd₁/C have different features in the hydrogen adsorption-desorption region from pure Pt/C catalyst. The catalytic activity of Pt₃Pd₁/C for ORR is a little improved compared with Pt/C or Pt₁Pd₁/C catalyst in RDE (rotating disk electrode) measurement. Detailed work reveals that the activity of ORR could be further improved on Pt-Pd/C catalyst with Pt rich on the metal nanoparticles surface. This point is consistent with the theoretical calculation results. DFT (Density Function Theory) studies on the adsorption and dissociation of O₂ on Pt- Pd cluster indicate that the presence of Pd atoms facilitates the dissociation of O₂ on Pt sites.