Synergistic Integration of MXene and Graphene with Ni3S2/Co9S8 Heterostructures into a Hierarchical Nanoarray for Ultrahigh-Capacity Supercapacitors

Abstract The pursuit of high-energy-density supercapacitors urgently demands materials that combine high specific capacity, fast charge/discharge capability, and stable operation under long-term cycling conditions. Nevertheless, typical transition-metal sulfides such as Ni3S2 and Co9S8, possess abundant faradaic redox active sites yet suffer intrinsic drawbacks upon repeated charging–discharging. Herein, a hierarchically engineered MXene-wrapped nickel–cobalt sulfide composite nanoarray on a graphene-coated nickel foam skeleton (denoted MNCSG) is constructed via a three-step hydrothermal method. The reduced graphene oxide (rGO) scaffold that provides a three-dimensional deposition backbone, uniformly grown Ni3S2/Co9S8 heterostructures as high-capacity electroactive phases, and an outer Ti3C2Tx MXene coating that serves as a conductive buffer layer to accommodate volume changes and enhance interfacial charge transfer. Benefiting from this synergistic design of 3D deposition/conductive scaffold─surface capacitance modification─interfacial stress buffering, the MNCSG electrode exhibits high specific capacity of 1288.8 C g–1 (6.29 C cm–2) at 1 A g–1 and maintains 47% of its capacity at 20 A g–1, indicating superior rate capability. Moreover, for the fabricated MNCSG//N-rGO/NF hybrid supercapacitor device, an energy density of 45.6 Wh kg–1 is obtained under 800 W kg–1 power output. After undergoing 8000 repeated cycling tests, the device still preserves 78.1% of the initial capacitance, confirming robust cyclic performance. The work not only establishes a generic strategy for integrating MXene and graphene with sulfides to overcome intrinsic kinetic and stability bottlenecks, but also provides profound insights into hierarchical interface engineering toward next-generation high-energy-density supercapacitors.