Redox-Active Electronic Structure Engineering in Nitrogen-Doped Graphene Quantum Dots for Oxygen Reduction Electrocatalysis

Electronic structure regulation and redox interfacial processes collectively govern the oxygen reduction reaction (ORR) activity of nitrogen-doped graphene quantum dots (N-GQDs), positioning these materials as emerging metal-free electrocatalysts for sustainable energy conversion technologies. This review examines how nitrogen bonding configurations, defect topology, quantum confinement, and interfacial electronic coupling influence redox kinetics, oxygen-intermediate stabilization, and charge-transfer pathways during ORR. Particular emphasis is placed on the redox-active nature of edge-dominated N-GQD architectures, where local spin density, charge polarization, and dynamic surface chemistry cooperatively determine catalytic performance. Recent advances in heteroatom co-doping, hybrid nanoarchitectures, and conductive support integration are analyzed to elucidate their roles in modulating electron-transfer efficiency and oxygen reduction mechanisms. Beyond conventional activity metrics, this review highlights the importance of interfacial redox processes, including catalyst–electrolyte interactions, surface functional-group evolution, and dynamic active-site reconstruction under electrochemical operating conditions. Emerging operando spectroscopic approaches and descriptor-guided theoretical models are discussed as essential tools for establishing experimentally verifiable structure–redox activity relationships. Furthermore, the multifunctional role of N-GQDs as redox-active electronic mediators in oxygen electrocatalysis, redox flow batteries, and related electrochemical energy systems is evaluated to provide a broader perspective on their functional significance. These redox-active and electronically tunable characteristics may also support emerging biomedical applications, particularly electrochemical biosensing, redox-responsive biointerfaces, and oxygen-related diagnostic platforms, where controlled interfacial electron transfer is central to signal generation and biological redox monitoring. By integrating concepts from redox chemistry, interfacial electrochemistry, and nanoscale electronic engineering, this review outlines current challenges and future directions toward the rational design of high-performance and scalable N-GQD-based electrocatalysts.

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