Metal Cation Pre-Intercalated Ti₃C₂T_x MXene as Ultra-High Areal Capacitance Electrodes for Aqueous Supercapacitors

Two-dimensional transition-metal carbides and nitrides “MXenes” have demonstrated great potential as electrode materials for electrochemical energy storage systems. This is especially true for delaminated Ti3C2Tx, which already shows outstanding gravimetric and volumetric capacitance, with areal capacitance limited by thickness (only a few microns). However, the performance of multilayer Ti3C2Tx has been more modest. Here, we report on using metal cation (viz., Na+, K+, and Mg2+) pre-intercalated multilayer Ti3C2Tx as electrodes for aqueous supercapacitors. These electrodes are scalable and amenable to roll-to-roll manufacturing, with adjustable areal loadings of 5.2 to 20.1 mg/cm2. K–Ti3C2Tx exhibited the highest capacitances at different scan rates. A gravimetric capacitance comparable to that of delaminated MXene of up to 300 F/g was achieved for multilayer K–Ti3C2Tx but with an outstanding ultra-high areal capacitance of up to 5.7 F/cm2, which is 10-fold higher than the 0.5 F/cm2 of delaminated MXene and exceeds the 4.0 F/cm2 of microengineered MXene electrodes.