Recent Advances in Mxene Quantum Dots for High-Performance Supercapacitor Applications: Synthesis, Mechanisms, and Future Prospects.

MXene quantum dots (MXQDs), produced by downsizing two-dimensional MXenes into zero-dimensional nanostructures, have emerged as promising materials for next-generation supercapacitors owing to their quantum confinement, metallic conductivity, abundant surface terminations, and excellent dispersibility. This review summarizes recent advances in MXQDs with emphasis on the synthesis structure-property-performance relationship governing their electrochemical behavior. Various synthesis strategies, including hydrothermal, microwave-assisted, laser-induced, and acousto-microfluidic methods, are discussed in relation to their effects on size, crystallinity, morphology, and surface chemistry. Advanced characterization techniques, including XRD, Raman, FTIR, TEM/HRTEM, and AFM, are highlighted for elucidating crystal structure, defect states, and surface functional groups. The effects of quantum confinement, heteroatom doping, defect engineering, and surface terminations on charge-transfer kinetics, ion diffusion, and pseudocapacitive behavior are critically examined. Furthermore, recent developments in MXQD-based electrode architectures, including carbon-, hydroxide-, and conducting polymer-based composites, as well as flexible and transparent supercapacitors, are evaluated with respect to their electrochemical performance. Finally, the remaining challenges, including precise control of surface terminations, aggregation, long-term stability, and scalable synthesis, are discussed together with future perspectives for the rational design and practical implementation of high-performance MXQD-based supercapacitors.