Observing the Structural Evolution of Quasi-Monolayer Pt Shell on Pd Core in the Electrocatalytic Oxygen-Reduction Reaction

The use of a quasi-monolayer Pt shell(Pt-qms) on a Pdcore (Pd-c) can reach cost and activity targets for theelectrocatalytic oxygen-reduction reaction (ORR). The structure ofPd(c)Pt(qms) in the ORR will vary; however, directobservation of this issue is scarce. Here, during cyclic staircasevoltammetry (ranging from 0.5 to 1.15 V-RHE) in 0.1 M O-2-saturated HClO4, the structure of PdcPtqms was monitored by in situ X-ray absorption spectroscopy.The qualitative and quantitative structural information clearly exhibitsa complete picture that Pt-qms will directly restructureto form Pt clusters and holes, while Pd-c almost remainsstable. These findings identify the initial structural evolution ofPd(c)Pt(qms) in the ORR, highlighting the importanceof protecting Pd-c in the development of high-performancePd(c)Pt(qms) electrocatalysts.