MXene quantum dots in catalysis and energy conversion: structure-activity insights and emerging prospects.

MXene quantum dots (MQDs) have emerged as a promising nanoscale platform for sustainable energy conversion. Owing to quantum confinement, MQDs exhibit discrete electronic states and a high surface-to-volume ratio, while inheriting the excellent electrical conductivity and chemical tunability of their parent MXenes. These combined features provide abundant edge-active sites and efficient charge transport, enabling MQDs to perform effectively in electrocatalytic and photocatalytic reactions. In many cases, MQDs demonstrate catalytic activity comparable to that of noble-metal catalysts, without dependence on rare elements. This work systematically examines the structure-activity relationships governing MQD performance, with a focus on the roles of heteroatom doping, surface terminations, and hybrid material design in regulating adsorption behaviour, redox kinetics, and charge-transfer processes. Particular attention is given to how quantum confinement and edge chemistry modify electronic structures and reaction energy barriers, as revealed by complementary experimental characterization and theoretical modelling. The discussion further extends to electrochemical energy-storage applications and the industrial potential of MQD-based materials. In these systems, MQDs shorten ion-diffusion pathways, enhance electrode-electrolyte contact, and promote faradaic charge-storage mechanisms, indicating substantial opportunities for future development. Despite these advances, challenges remain, including limited long-term stability, incomplete understanding of active sites, and the need for scalable synthesis with precise control over surface chemistry. Addressing these issues through rational material design and