Graphene quantum Dots-Based Materials: Concepts, Engineering, Advances, and challenges towards electrochemical energy systems

Graphene quantum dots (GQDs) are next-generation class of zero-dimensional carbon-based nanomaterials exhibit variable bandgap energies and quantum dimensional effect suitable for advanced electrochemical energy conversion and storage applications. Their intrinsic properties such as high specific surface area, chemical versatility, and electrochemical stability increase their performance characteristics in electrocatalytic systems, batteries, and supercapacitors. GQDs is an exceptional support for anchoring various active materials, such as metal nanoparticles or metal oxides, providing an accelerated interfacial charge transport through highly conductive pathways between active sites and the electrode resulting improved in overall catalytic efficacy. Moreover, atomic scale disorder, edge sites/defects and functional groups (–OH, –COOH, −C=O etc.) on GQD surface furnish an additional active site for electrocatalytic processes. Heteroatom doping (N, S, B, and P) further create electron density states, promote charge delocalization, es and facilitates favourable adsorption/desorption reaction intermediates. Within this context of energy storage, GQDs can intercalate Li/Na-ions and modulate ion diffusion kinetics due to redox active (surface) functional groups and interlayer spacing. Additionally, their pseudo-capacitance behaviour also significantly contributes to supercapacitors and portraying them as promising electrode materials for hybrid capacitors. Despite these advances, a comprehensive evaluation of the electrochemical performance and structural attributes of GQDs in relation to their applied energy technologies remain unexplored. This review inspects current progress in the design and development of GQDs for electrochemical energy conversion and storage systems. Firstly, we presented a fundamental understanding of a sustainable and cost-effective synthesis strategies, specifically focus on atomically precise structural engineering design. Furthermore, the intrinsic electronic structure and morphological features of GQDs are examined in correlation with their redox behaviour and charge transfer kinetics. Attention is also paid to establishing structure–property-performance correlations that underpin their functional role in electrochemical systems. Moreover, this review provides a critical outlook on the prospects, prevailing challenges, and future directions associated with the deployment of GQDs in next generation energy technology.