Iodine-Functionalized Titanium Carbide MXene with Ultra-Stable Pseudocapacitor Performance

MXene has attracted a wide spread attention as promising supercapacitor electrode materials owing to excellent electronic conductivity and reversible surface redox capability. In fact, the supercapacitor performance strongly relies on   surface terminations of MXene. However, regulating the types of surface terminations for enhancing the electrochemical performance of MXene is still one of major challenge. Herein, we successfully prepared a MXene containing iodine terminations (I-Ti 3 C 2 MXene) by facile Lewis-acidic-melt etching method and comprehensively investigated its supercapacitor performance. Benefiting from the presence of iodine terminations, the I-Ti 3 C 2 MXene with pseudocapacitor property exhibits significantly higher specific capacitance than that of hydrofluoric acid etching MXene (HF-Ti 3 C 2 T x MXene). Impressively, the I-Ti 3 C 2 MXene shows extraordinary long-term cyclic performance, even when cycled at high current density of 50 A/g, that the specific capacitance retention of 91% can be obtained over 100,000 cycles, corresponding to an average specific capacitance loss of only 0.00009% per cycle. Furthermore, the mechanisms involved were clarfied by systematical characterizations. This work will provide new insights for enhancing the supercapacitor performance of MXene-based materials by surface chemistry modification.