High-performance asymmetric supercapacitors based on a 3D Ti3C2TX@NiCo2S4-reduced graphene oxide hydrogel positive electrode

Abstract

To enhance the energy density of supercapacitors (SCs), the development of heterostructures and the use of asymmetric device architecture are effective strategies. MXenes, known for their excellent physicochemical properties, have emerged as promising electrode materials for energy storage systems. In this study, negatively charged NiCo₂S₄ nanoflowers were uniformly anchored onto the surface of the positively charged Ti₃C₂T_X substrate through electrostatic assembly, creating a hierarchical Ti₃C₂T_X@NiCo₂S₄ heterostructure. This heterostructure was further assembled into a 3D porous hydrogel using a hydrothermal graphene oxide (GO)-assisted self-assembly process. The resulting 3D hierarchical Ti₃C₂T_X@NiCo₂S₄-reduced graphene oxide (RGO) hydrogel exhibited an ultrahigh specific capacitance of 496 F g⁻¹ at 1 A g⁻¹, significantly outperforming the Ti₃C₂T_X-RGO hydrogel, which had a specific capacitance of 164.2 F g⁻¹. Additionally, the defective RGO (DRGO) hydrogel showed a substantial increase in specific capacitance compared to untreated RGO (339 F g⁻¹ vs. 95 F g⁻¹ at 1 A g⁻¹) due to the presence of abundant mesopores. These materials were then utilized as free-standing positive and negative electrodes to construct asymmetric supercapacitors (ASCs), which demonstrated a wide operating voltage range (−1 to 1 V), a high energy density (70 W h kg⁻¹ at 1000 W kg⁻¹ and 37.6 W h kg⁻¹ at 10 000 W kg⁻¹), and excellent cycling stability (91% capacitance retention after 10 000 cycles at 10 A g⁻¹). This study underscores the potential of 3D MXene-based heterostructured hydrogels as highly effective electrode materials for supercapacitors.