Pd 4d Orbital Overlapping Modulation on Au@Pd Nanowires for Efficient H₂O₂ Production

Isolating Pd atoms has been shown to be crucial for the design of a Pd-based electrocatalyst toward 2e^- oxygen reduction reaction (ORR). However, there are limited studies focusing on the systematic compositional design that leads to an optimal balance between activity and selectivity. Herein, we design a series of Au@Pd core@shell structures to investigate the influence of the Pd 4d orbital overlapping degree on 2e^- ORR performance. Density functional theory (DFT) calculations indicate that enhanced H₂O₂ selectivity and activity are achieved at Pd clusters with n ≤ 3, and Pd clusters larger than Pd₃ should be active for 4e^- ORR. However, experimental results show that Au@Pd nanowires (NWs) with Pd₄ as the primary structure exhibit the optimal H₂O₂ performance in an acidic electrolyte with a high mass activity (7.05 A mg^-1 at 0.4 V) and H₂O₂ selectivity (nearly 95%). Thus, we report that Pd₄, instead of Pd₃, is the upper threshold of Pd cluster size for an ideal 2e^- ORR. It results from the oxygen coverage on the catalyst surface during the ORR process, and such an oxygen coverage phenomenon causes electron redistribution and weakened *OOH binding strength on active sites, leading to enhanced activity of Pd₄ with only 0.06 V overpotential in acidic media.