Density Functional Theory Study of the Relationship\nbetween N‑Dopants and Vacancy Defects on Graphene Quantum Dots\nfor Oxygen Reduction Electrocatalysis

Graphene\nquantum dots (GQDs), as novel zero-dimensional nanomaterials,\nhave demonstrated exceptional electrocatalytic activities, primarily\ndue to quantum confinement and edge effects. However, the relative\ncontributions of heteroatom doping versus defect induction to catalytic\nactivity as well as their interplay remain topics of ongoing research.\nIn this study, four different vacancy defects were introduced into\nthree distinct N-doped GQDs (graphitic-N, pyridinic-N, and pyrrolic-N)\nto investigate the synergistic effects of N-doping and defect induction\non the oxygen reduction reaction (ORR) catalytic performance of the\nGQDs. The structural configurations of these defect-/heteroatom coengineered\nGQDs and their structure–activity relationships were analyzed\nusing density functional theory methods at the B3LYP/6-311G(d,p) level.\nIn the ORR’s four-electron pathway, the formation of the *OOH\nintermediate was identified as a decisive step. The study revealed\nthat the synergistic effect of vacancy defects and nitrogen doping\nsignificantly reduced the adsorption energy of the *OOH intermediate\nin pristine GQDs. For example, the original GQDs exhibit an adsorption\nenergy of 6.32 eV with an overpotential of 2.63 V for the *OOH intermediate.\nNotably, introducing graphitic-N with a divacancy defect reduced the\nadsorption energy to 4.76 eV and the overpotential to 1.07 V. Furthermore,\nthe introduction of defects was found to induce curvature in the sp<sup>2</sup>-hybridized carbon atom sheets, thereby altering their electrocatalytic\nactivities. These findings highlight the crucial role of N-dopants\nand vacancy defects in lowering the activation energy barrier for\noxygen dissociation, thereby enhancing the ORR performance and advancing\nthe application of carbon-based nanomaterials in renewable energy\nconversion and storage devices.