Impact of graphene quantum dot edge shapes on high-performance energy storage devices

Abstract

Electrode materials critically influence the performance of energy storage devices such as supercapacitors and batteries. Graphene quantum dots (GQDs) are a promising material for next-generation systems due to their high surface-to-volume ratio, tunable bandgaps, and stability. Their nanoscale size creates numerous edge sites with zigzag (ZZ) or armchair (AC) configurations. Yet, the role of edge shape in electrochemical behavior remains largely unexplored. Likewise, the correlation between synthesis methods and edge configurations is unclear, hindering the development of targeted fabrication approaches. In this study, nitrogen-doped GQDs (N-GQDs) with ZZ and AC edges were synthesized via hydrothermal and electrochemical methods. They were subsequently characterized using physical methods (XRD, TEM, UV-Vis, Raman spectroscopy). They were then electrodeposited onto carbon fibers and their electrochemical properties were analyzed (CV, EIS). We examined the N-GQD size, edge configuration, bandgap, charge transport, and process parameters such as pH and electrolyte choice. The results show that ZZ-edged N-GQDs outperform AC-edged counterparts in capacitance (double-layer, pseudocapacitance, quantum capacitance) due to a higher density of states originating from dispersionless edge states, which are absent at AC edges. Additionally, pH variations affect ZZ N-GQDs by modulating their energy bandgap, informing electrolyte selection and material tuning to deliver target applications such as batteries or supercapacitors. This work establishes performance differences between ZZ and AC edged N-GQDs, enabling precise nanoparticle design for optimized energy storage, and opens opportunities in bandgap-engineered applications such as solar cells, LEDs, lasers, and photodetectors.