Metal-organic framework-derived NiCo2S4@Co3S4 yolk-shell nanocages/ Ti3C2Tx MXene for high-performance asymmetric supercapacitors

Ti3C2Tx MXene has become an excellent two-dimensional conductive substrate for electrode materials of supercapacitors (SCs) with prominent physicochemical properties. Whereas, due to the lower theoretical specific capacitance and its interlayer agglomerate, the practical application and electrochemical property of Ti3C2Tx have imposed serious restrictions. Herein, metal-organic framework (MOF) derived NiCo2S4 @Co3S4 nanocages with superior yolk-shell structure are introduced to anchor on the surface of Ti3C2Tx via ion exchange reaction and electrostatic attraction, forming the distinctive hierarchical structure of NiCo2S4 @Co3S4/Ti3C2Tx composed of NiCo2S4 @Co3S4 yolk-shell nanocages (NiCo2S4 @Co3S4 YSNs) adsorbed on 2D Ti3C2Tx nanosheets. The NiCo2S4 @Co3S4 YSNs with a large void space, serving as a confined reactor, not only offer a buffer against the volume variation, but also supply abundant active sites and restrain the ag-glomeration of Ti3C2Tx nanosheets. Furthermore, the novel structure of NiCo2S4 @Co3S4/Ti3C2Tx composite as electrode material could accelerate the thermodynamic stability, suppress the textural instability, and moderate the unavoidable volume change of active substance. Benefited from the above merits, the NiCo2S4 @Co3S4/Ti3C2Tx electrode demonstrates a significant specific capacitance (1872 F g-1 at 2 mV s-1), re-markable rate capability in the high current density (such as, 1121.6 F g-1 at 20 A g-1, 1533 F g-1 at 0.5 A g-1) and displays an excellent life span with 92.2 % of the capacity retention after 12,000 cycles at 10 A g-1. More particularly, the asymmetric supercapacitors (ASCs) fabricated with NiCo2S4 @Co3S4/Ti3C2Tx represent a fascinating energy density of 241.9 Wh kg-1 at a power density of 1125 W kg-1, which can light up 10 LEDs simultaneously. The results further prove that this rational design method could provide a meaningful prospect for MXenes and MOF derivatives composites for high-performance ASCs.(c) 2023 Elsevier B.V. All rights reserved.