Pt 5d Density of States in Pt₃Mg–N–C Catalyst Governed by Ligand Effect

In alloy systems, the strain and ligand effects are prevalent, but it is challenging to study the impact of either on the material structure independently. We conducted high-energy-resolution fluorescence detection (HERFD) X-ray absorption spectroscopy (XAS) and resonant X-ray emission spectroscopy (XES)/resonant inelastic X-ray scattering (RIXS) spectroscopy on a Pt₃Mg alloy-based carbon material (Pt₃Mg-N-C). By introducing a size-comparable atom, the strain effect is minimized, allowing the Pt d-density of states (d-DOS) to be primarily affected by the ligand effect. The experimental results reveal that Pt gains electrons in Pt₃Mg-N-C, exhibiting a more symmetric d-band shape and a downshift of the d-band center compared to Pt metal, which is further confirmed by density functional theory (DFT) calculations. The correlation between the Pt d-DOS and oxygen reduction reaction (ORR) activity is also discussed.