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

Abstract

Two-dimensional (2D) MXene materials have significant potential applications in electrochemical energy storage. A Ti3C2Tx MXene film can be used as a high-performance electrode for a flexible supercapacitor owing to its flexibility and excellent rate capability. However, Ti3C2Tx 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 Ti3C2Tx nanosheets and 1D MnO2 nanobelts to form an alternating MnO2/Ti3C2Tx stacked structure. Compared with pure Ti3C2Tx, the hybrid cathode has higher electrochemical stability toward anodic oxidation. The MnO2/Ti3C2Tx 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 MnO2/Ti3C2Tx hybrid cathode is mainly attributed to the charge transfer-induced work function enlargement at the Ti3C2Tx and MnO2 heterointerface. Furthermore, a flexible asymmetric supercapacitor assembled using MnO2/Ti3C2Tx as the cathode and alkalized Ti3C2Tx 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.