Superior pseudocapacitive performance and mechanism of self-assembled MnO2/MXene films as positive electrodes for flexible supercapacitors

Two-dimensional (2D) MXene materials have significant potential applications in electrochemical energy storage. A Ti 3 C 2 T x MXene film can be used as a high-performance electrode for a flexible supercapacitor owing to its flexibility and excellent rate capability. However, Ti 3 C 2 T x is usually only used as a negative electrode material because it can be easily oxidized under positive (anodic) potential. Herein, we report a simple filtration method to fabricate a hybrid cathode by mixing a colloidal solution of 2D Ti 3 C 2 T x nanosheets and 1D MnO 2 nanobelts to form an alternating MnO 2 /Ti 3 C 2 T x stacked structure. Compared with pure Ti 3 C 2 T x , the hybrid cathode has higher electrochemical stability toward anodic oxidation. The MnO 2 /Ti 3 C 2 T x hybrid cathode delivers a high gravimetric capacitance of 315 F g −1 at 10 mV s −1 and a good rate capability of 166 F g −1 at 100 mV s −1 . The high stability of the MnO 2 /Ti 3 C 2 T x hybrid cathode is mainly attributed to the charge transfer-induced work function enlargement at the Ti 3 C 2 T x and MnO 2 heterointerface. Furthermore, a flexible asymmetric supercapacitor assembled using MnO 2 /Ti 3 C 2 T x as the cathode and alkalized Ti 3 C 2 T x as the anode delivers a high-voltage window up to 1.9 V. This work provides new insights for designing high-performance MXene-based cathode materials and devices for wearable electronics.