3D hierarchical transition-metal sulfides deposited on MXene as binder-free electrode for high-performance supercapacitors

MXene has been considered as a promising two-dimensional material for supercapacitors owing to its large surface area, high conductivity, and excellent cycling stability. However, its low specific capacitance restricts its extensive applications. Therefore, to address the issue, we homogeneously deposited NiCo2S4 nanoflakes on the surface of MXene on conductive nickel foam (denoted as MXene-NiCo2S4@NF), which was used as a composite binder-free electrode for supercapacitor applications. The NiCo2S4 nanoflakes increased the surface area of the composite electrode, thereby increasing its specific capacity from 106.34 C g-1 to 596.69 C g-1 at 1 A g-1. Compared to the pristine MXene, MXene-NiCo2S4@NF maintained the high retention rate of pristine MXene and exhibited excellent cycling stability with 80.4% of its initial specific capacity after 3000 cycles. The composite electrode exhibited improved electrochemical performance for supercapacitors, owing to the combined merits of NiCo2S4 (high specific capacity) and MXene (high retention rate and good cycling stability. The fabricated asymmetric solid-state supercapacitor using MXene-NiCo2S4 as a positive electrode and active carbon as a negative electrode, exhibited an energy density of 27.24 Wh kg-1 at 0.48 kW kg-1 of power density.