Sulphate (–S) and Phosphate (–P) Surface-Functionalized Ti3C2T x MXene for Enhanced Supercapacitor and Electromagnetic Wave Absorption Performances

Two-dimensional MXene materials have emerged as promising electrode materials for supercapacitors owing to their high electrical conductivity, superior redox behavior, hydrophilicity, and tunable surface chemistry. However, the electrochemical performance of MXene phases is often limited by layer restacking, restricted ion accessibility, and insufficient pseudocapacitive activity. Surface-functionalized Ti3C2Tx significantly improves the adsorption properties of MXene phases by adding functional groups that provide reactive sites. In this study, the Ti3C2Tx MXene phases were systematically functionalized with sulphate (SO42-) and phosphate (PO43-) groups through selective acidic treatments using H2SO4/HF (Tx: -F, -OH, SO42-) and H3PO4/HF (Tx: -F, -OH, PO43-) solutions. Structural, morphological, and surface chemical analyses confirm the successful incorporation of SO42- and -PO43--based functional groups without altering the Ti3C2Tx crystal structure. The SO42- and PO43- surface-functionalized MXene phases exhibit markedly enhanced pseudocapacitive behavior, reduced charge-transfer resistance, and improved ion transport kinetics compared with bare Ti3C2Tx MXene. The SO42--functionalized Ti3C2Tx MXene phases displayed an outstanding specific capacitance of 466 F g-1 at 2 A g-1 and best thickness-tolerant absorption behavior with a minimum reflection loss of -42.6 dB, while the deepest RL value of -55.3 dB at 1.5 mm was obtained for Ti3C2Tx MXene.