Nitrogen-doped carbon quantum dots (N-CQDs) have emerged as promising candidates for enhancing the pseudocapacitance of graphene-based supercapacitors. However, the intrinsic relationship between heteroatom doping, the resultant microstructural evolution, and the macroscopic electrochemical behavior remains inadequately understood. In this study, para-aminobenzoic acid was innovatively selected as a precursor that simultaneously serves as a nitrogen source and a surface-functionalizing agent. A nitrogen-doped carbon quantum dot/reduced graphene oxide (N-CQDs/rGO) composite was successfully synthesized via a hydrothermal method, aiming to systematically investigate the intrinsic correlation between doping-induced microstructural changes and macroscopic electrochemical performance. Materials characterization confirmed the successful incorporation of nitrogen into the composite, giving rise to multiple nitrogen configurations, including pyridinic N, pyrrolic N, and graphitic N. This doping significantly increased structural defects and surface wrinkles. In a three-electrode system using 6 M KOH as the electrolyte, the N-CQDs/rGO electrode exhibited excellent electrochemical performance. At a current density of 1 A g-1, it delivered a specific capacitance of 201.2 F g-1, substantially higher than those of pure rGO (150.3 F g-1) and undoped CQDs/rGO (76.0 F g-1). Electrochemical impedance spectroscopy revealed extremely low charge transfer resistance and internal resistance. Kinetic analysis indicated that the charge storage mechanism is predominantly governed by surface capacitive effects, with a capacitive contribution of 92.1% at a scan rate of 100 mV s-1. Moreover, after 10,000 charge-discharge cycles at a high current density of 10 A g-1, the electrode retained 88.2% of its initial capacitance, demonstrating outstanding cycling stability. The practical application potential of N-CQDs/rGO was further validated using a symmetric supercapacitor assembled from this material. The device achieved an energy density of 9.99 Wh kg-1 at a power density of 250 W kg-1. After 10,000 charge-discharge cycles at a current density of 5 A g-1, the device retained 98.36% of its initial capacitance with a Coulombic efficiency approaching 100%. These results confirm that nitrogen doping effectively enhances the capacitance and rate performance of rGO-based composites by introducing pseudocapacitive active sites and optimizing charge/ion transport kinetics.

N-CQDs/rGO composites for supercapacitors: Role of nitrogen doping in microstructural evolution and capacitive enhancement

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发表日期：

2026年5月18日

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Qing Zhao,
Kai Wang,
Hong Chang,
Ying Li,
Rui Yan,
Shuai Jia

摘要

Nitrogen-doped carbon quantum dots (N-CQDs) have emerged as promising candidates for enhancing the pseudocapacitance of graphene-based supercapacitors. However, the intrinsic relationship between heteroatom doping, the resultant microstructural evolution, and the macroscopic electrochemical behavior remains inadequately understood. In this study, para-aminobenzoic acid was innovatively selected as a precursor that simultaneously serves as a nitrogen source and a surface-functionalizing agent. A nitrogen-doped carbon quantum dot/reduced graphene oxide (N-CQDs/rGO) composite was successfully synthesized via a hydrothermal method, aiming to systematically investigate the intrinsic correlation between doping-induced microstructural changes and macroscopic electrochemical performance. Materials characterization confirmed the successful incorporation of nitrogen into the composite, giving rise to multiple nitrogen configurations, including pyridinic N, pyrrolic N, and graphitic N. This doping significantly increased structural defects and surface wrinkles. In a three-electrode system using 6 M KOH as the electrolyte, the N-CQDs/rGO electrode exhibited excellent electrochemical performance. At a current density of 1 A g^-1, it delivered a specific capacitance of 201.2 F g^-1, substantially higher than those of pure rGO (150.3 F g^-1) and undoped CQDs/rGO (76.0 F g^-1). Electrochemical impedance spectroscopy revealed extremely low charge transfer resistance and internal resistance. Kinetic analysis indicated that the charge storage mechanism is predominantly governed by surface capacitive effects, with a capacitive contribution of 92.1% at a scan rate of 100 mV s^-1. Moreover, after 10,000 charge-discharge cycles at a high current density of 10 A g^-1, the electrode retained 88.2% of its initial capacitance, demonstrating outstanding cycling stability. The practical application potential of N-CQDs/rGO was further validated using a symmetric supercapacitor assembled from this material. The device achieved an energy density of 9.99 Wh kg^-1 at a power density of 250 W kg^-1. After 10,000 charge-discharge cycles at a current density of 5 A g^-1, the device retained 98.36% of its initial capacitance with a Coulombic efficiency approaching 100%. These results confirm that nitrogen doping effectively enhances the capacitance and rate performance of rGO-based composites by introducing pseudocapacitive active sites and optimizing charge/ion transport kinetics.