A Ti3C2Tx@PANI core–shell heterostructure assembled into a 3D porous hydrogel as a free-standing electrode for high-energy supercapacitors

Abstract

Although Ti₃C₂T_x MXenes have attracted attention in electrochemical energy storage devices due to their excellent electronic conductivity, controllable layer structure, and huge redox active surface area, the application of Ti₃C₂T_x as supercapacitor (SC) electrode materials is severely limited by the ineffective chemical ion transport kinetics caused by self-restacking. In order to increase the interlayer spacing of Ti₃C₂T_x, the intercalation method is hailed as an effective process. Herein, polyaniline (PANI) nanorods as intercalators were synthesized by the polymerization of an aniline (ANI) monomer chemisorbed onto Ti₃C₂T_x wrinkled nanosheets, and the formation of a Ti₃C₂T_x@PANI heterostructure is conducive to the large interlayer voids. Then, the heterostructure was integrated into a three-dimensional (3D) porous cross-linked framework via a simple graphene oxide (GO)-assisted self-convergence hydrothermal strategy with low temperatures. Due to the synergistic effect among each component and 3D porous interconnected structure, the hierarchical Ti₃C₂T_x@PANI-reduced graphene oxide (RGO) heterostructure hydrogel possesses the advantages of excellent electrical conductivity, high specific capacitance, repressive aggregation, and large electrochemical active area. Heterostructure hydrogel electrodes (without binders) display excellent electrochemical performance with a specific capacitance as high as 301.0 F g⁻¹ at 1 A g⁻¹, 90.74% capacitance retention over 10 000 cycles, and a maximum energy density of 44.6 W h kg⁻¹ at a power density of 504.7 W kg⁻¹. Our study provides a fresh strategy for constructing a 3D Ti₃C₂T_x-based framework applicable to other MXenes in the design of hybrid structures for maximizing their potential applications in energy storage.