Designed Redox‐Electrolyte Strategy Boosted with Electrode Engineering for High‐Performance Ti3C2Tx MXene‐Based Supercapacitors

Abstract Ti 3 C 2 T x MXene has shown remarkable potential for supercapacitors. However, its limited capacitance restrains the energy density. Here, a designed redox‐electrolyte strategy boosted with electrode engineering for Ti 3 C 2 T x MXene is demonstrated, by which a record‐high specific capacitance of 788.4 F g −1 at 2 mV s −1 is achieved, accompanied by good rate capability and highly improved cyclic stability compared with the pristine MXene electrode. For the first time, redox additives with redox potentials falling in the Ti 3 C 2 T x MXene's potential range and that can take full advantage of the characteristics of Ti 3 C 2 T x MXene are investigated. CuSO 4 and VOSO 4 are screened as the hybrid redox additives; and it is revealed that copper and vanadium ions can bond with ═O terminals on the MXene surface and undergo redox reactions mainly via Cu 2+ /Cu + and V 3+ /V 2+ . The electrode engineering significantly boosts the designed redox‐electrolyte strategy by enhancing ion dynamics and increasing electrochemically active sites. High energy density of 80.9 Wh kg −1 at a power density of 376.0 W kg −1 and high cyclic stability and improved self‐discharging behavior are obtained for the fabricated supercapacitor by applying this strategy. The strategy is also demonstrated for the performance improvement of MXene‐based flexible supercapacitors with hydrogel electrolytes.