Quantitatively Determining the Size Effect of Pd Core on the Strain and Activity of Quasi-Monolayer Pt Shell for the Oxygen-Reduction Electrocatalysis

The use of core–shell nanoparticles composed of Pd core (Pdc) and quasi-monolayer Pt shell (Ptqms) for the oxygen reduction reaction (ORR) facilitates reaching the fuel-cell performance and cost targets. However, explicit guidelines for regulating the structure of PdcPtqms to boost ORR remain unclear. Here, using in situ X-ray absorption spectroscopy and electrochemical measurement, we have quantitatively explored the size effect of Pdc on the strain and activity of Ptqms for the ORR. Employed Pdc samples only have different sizes, without other structural changes such as facets and roughness. When the size of Pdc increases, both the Pt–Pt bond distance and the ORR activity of Ptqms exhibit slightly linear increases. The Pt–Pt distance and ORR activity of Ptqms on different-sized Pdc also exhibit a linear relationship, which is located at the left side of our previously reported volcano-type strain–activity plot. These findings identify that although the size effect of Pdc is not the decisive factor, it can be used for assisting other structural properties of Pdc to control the strain and activity of Ptqms as well as decrease the total cost of PdcPtqms electrocatalysts.