<p>The MXenes are a class of two-dimensional transition metal carbide, nitride and carbonitride materials that have emerged as promising materials for electrochemical energy storage applications. Their outstanding electrical conductivity, tunability of surface chemistry and high volumetric capacitance make them promising materials for next generation of supercapacitors and batteries. This comprehensive overview summarises the need for surface functionalization and electrochemical performance in MXene-based electrodes. The different surface termination groups on MXenes (O, −OH, −F, −Cl, −Br) are systematically analysed to understand their effect on charge storage mechanisms such as electric double-layer capacitance (EDLC), pseudo capacitance, and ion intercalation. It presents both traditional and novel Hydrofluoric Acid (HF) and fluorine-free synthesis approaches and explores their influence on the surface chemistry and electrochemical properties. More specifically, surface terminations can efficiently manage how charge is stored by governing interfacial ion adsorption, wettability, and the redox activity of the electrode surface. Oxygen- and hydroxyl-rich terminations classically improve pseudocapacitance via surface redox reactions and endorse satisfactory ion transport by raising hydrophilicity and interlayer water content that can aid faster electrolyte access throughout cycling. On the other hand, more electronegative or fluorine-rich terminations can adjust the surface charge distribution and ion–surface interactions, particularly causing a suppressed electrochemical activity, higher capacitance loss, and decreased ion mobility. Indeed, realising these termination chemistries would enable MXenes to shift between dominant mechanisms like EDLC, pseudo-capacitance, and ion intercalation, thus would influence both capacitance and rate performance. Statistically, the quantitative performance measurements represent that gravimetric capacitances of more than 471 F/g, volumetric capacitances up to 2000 F/cm³, cycling stabilities of above 97% after 20,000 cycles can be attained. The b-value analysis and mechanistic studies are specifically used to identify the significant charge storage pathways for different types of MXene systems. The possible methods of enhancing the performance by surface engineering techniques such as atomic surface reduction, controlled oxidation, heteroatom doping and intercalation, are critically evaluated. Comparative analysis shows that optimised interlayer water content with oxygen terminations is able to provide better pseudocapacitive behavior with reduced capacitance loss, whereas fluorine terminations generally have a negative effect on ion transport and capacitance loss. Overall, this review summarises all the necessary information for understanding the rational design of high-performance electrodes based on MXenes, including synthesis methods, surface chemistry, charge storage mechanisms, and electrochemical performance.</p>