3D hierarchical Ti3C2Tx@NiCo2S4–RGO heterostructure hydrogels as free-standing electrodes for high-performance supercapacitors

Abstract

In order to push the energy density limit of supercapacitors (SCs), the strategy of developing heterostructure composites is feasible. Currently, MXenes with favorable physicochemical properties are promising electrode materials for energy storage systems. Herein, by electrostatic assembly, negatively charged NiCo₂S₄ nanoflowers were uniformly anchored onto the surface of positively charged Ti₃C₂T_x substrates to form a hierarchical Ti₃C₂T_x@NiCo₂S₄ heterostructure, which was then assembled into a 3D porous hydrogel by a hydrothermal graphene oxide (GO)-gelation self-convergence process at low temperatures. The resultant 3D hierarchical Ti₃C₂T_x@NiCo₂S₄–reduced graphene oxide (RGO) heterostructure hydrogel displayed an ultrahigh specific capacitance of 717.1 F g⁻¹ at 1 A g⁻¹, in comparison to that of the Ti₃C₂T_x–RGO hydrogel (155.5 F g⁻¹). As a result, the heterostructure hydrogel was then used as electrodes to construct a SC device, which exhibited a high energy density (73.86 W h kg⁻¹ at 300.1 W kg⁻¹ and 42.97 W h kg⁻¹ at 7111.7 W kg⁻¹), and a remarkable cycling stability (retention of 98.5% of the capacitance after 10 000 cycles at 10 A g⁻¹). This study highlights the unique potential of the 3D MXenes-based heterostructure hydrogel as a favorable electrode material for SCs.