Pd 4d Orbital Overlapping Modulation on Au@Pd Nanowires for Efficient HO 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 HO selectivity and activity are achieved at Pd clusters with ≤ 3, and Pd clusters larger than Pd should be active for 4e ORR. However, experimental results show that Au@Pd nanowires (NWs) with Pd as the primary structure exhibit the optimal HO performance in an acidic electrolyte with a high mass activity (7.05 A mg at 0.4 V) and HO selectivity (nearly 95%). Thus, we report that Pd, instead of Pd, 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 Pd with only 0.06 V overpotential in acidic media.