<p>Nitrogen-doping has been proposed as a method to enhance the performance of Pt-based electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Although various nitrogen-doping configurations exist, the active sites in nitrogen-doped carbon supported Pt nanoparticle electrocatalysts remain unclear. In this study, we synthesized carbon supported Pt nanoparticles with high purity of pyridinic and pyrrolic nitrogen using a soft nitriding method, minimizing the presence of other nitrogen species. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that N-doped materials promoted more uniform and smaller Pt particle deposition due to the increased binding energy between Pt atoms and pyrrolic/pyridinic nitrogen atoms at carbon matrix vacancies. X-ray photoelectron spectroscopy (XPS) analysis indicated an increase in the Pt²⁺ oxidation state ratio from 36% to 48.0%, indicating enhanced electron transfer from Pt nanoparticles to the N-doped carbon substrates. The Pt/N-doped electrocatalyst achieved a mass activity of 0.595 A mg-1 Pt, which is 3.3 times higher than that of the Pt/N-free electrocatalyst. Similar activity enhancements were observed in nitrogen-doped electrocatalysts using high-surface-area carbon support (BP2000) and high loading Pt (40 wt%). In addition, density functional theory (DFT) calculations revealed that strong interactions between Pt clusters and pyridinic/pyrrolic nitrogen substrates result in a favorable oxygen adsorption energy at the electrocatalytic interface, elucidating the intrinsic mechanism through which pyridinic/pyrrolic nitrogen doping enhances electrocatalytic activity.</p>