Solvent-assisted assembly of reduced graphene oxide/MXene-polypyrrole composite film for flexible supercapacitors

Two-dimensional (2D) materials represented by graphene and MXene have attracted extensive attention in the field of energy storage. However, the automatic stacking and poor stability of 2D materials considerably limit their electrochemical performance. In this article, we apply a design strategy based on combining the ternary components of reduced graphene oxide (rGO), MXene, and polypyrrole (PPy) into one electrode to form a flexible film with a sandwich structure. As a result, the resulting rGO/MXene-PPy composite electrode inherits the characteristics of high conductivity, robust mechanical properties, and pseudocapacitance. In addition to providing capacitive contributions, the PPy serves as a blocker to prevent face-to-face restacking of the 2D nanosheets and also as a coating layer to significantly protect MXene from oxidation. Consequently, the rGO/MXene-PPy electrode exhibits a high specific capacitance of 408.2 F g-1 and a superior rate performance, with 67.3% capacitance retention at an increased current density of 10.0 A g-1. Furthermore, the as-assembled asymmetric supercapacitor possesses a pronounced energy density of 11.3 Wh kg-1 (35.5 Wh L-1) at a power density of 500.0 W kg-1 (1570.0 W L-1) and remarkable cycling stability, with 8.8% capacitance deterioration after 10,000 cycles. This work demonstrates the potential for application of as-prepared rGO/MXene-PPy electrodes in flexible energy storage devices with high volumetric/gravimetric energy and power densities.