Figure 5: DFT studies of the ORR on Pd islands.
(a) Geometrically optimized structures showing the Pd–W nanoparticles with Pd–W2, Pd2W, Pd3 and Pd4 catalytic sites (Pd blue, W grey). (b) Oxygen reduction scheme used to study the catalytic activity (O red and H white). (c) Change in Gibbs free energy during ORRs performed on a Pd4 island of the Pd–W cluster at two different oxygen coverage, zero (θO=0) and half of a monolayer (θO=1/2), and under the effect of the electric field generated by the solvent, see also Supplementary Figs 15–17. The ORR is initiated by the adsorption of ½ O2 on the catalytic site, followed by the transfer of two proton–electron (H++e−) pairs, that results in the formation and release of one water molecule. (d) Activity volcano plot for diverse catalytic sites in Pd24W151 nanoparticles. The activity of catalytic sites located at the center of the particle facet is in blue, whereas red indicates islands at the edge. Pt, Pd, Ag and Au periodic surfaces (open circles) are shown for comparison, information taken from ref. 42. The inset shows the ORR activity of the materials near the top of the volcano, the red-open-diamond indicates the activity of a Pd4 island considering the effect of the solvent. The dashed line is a guide to the eyes.
