Flexible and Free-Standing MXene/Redox-Active Dye Molecules on Nanofibers for High-Performance Symmetric Supercapacitors

Molecular assembly of electrochemically active organic materials on nanostructures is considered one of the most effective energy storage materials. However, direct implementation of them in energy storage systems is mainly limited due to their low electrical conductivity and cycle life. An effective approach to enhance the electronic/ionic conductivity and stability of organic materials is to hybridize them with conductive 2D transition metal carbides and/or nitrides, so-called MXenes, which have excellent electronic and ionic conductivities and abundant tunable surface functional groups. In this study, we introduce a binder-free and flexible electrode by assembling Nile blue (NB) as a redox-active material with MXene to significantly enhance the specific capacity and cycling stability. In addition, Aramid nanofibers (ANFs) have been used to increase the mechanical strength of the electrode film and expand the interlayer distance of MXene layers, which accelerates ion transfer and provides more available redox-active sites for Faradaic reactions. The as-fabricated MX-ANF-NB electrode presents a much higher capacitance of 581 F g–1 at 1 A g–1 in a three-electrode system with excellent rate performance and low charge transfer resistance. Moreover, the MX-ANF-NB symmetric device shows an optimum energy density of 9.4 W h kg–1, a specific power of 8.1 kW kg–1, considerable flexibility, and a superior capacitance retention of 91% after 10,000 charge–discharge cycles at 5 A g–1. This finding opens a viable approach for the design of a high-performance and cost-effective supercapacitor based on electroactive organic materials.